Anne-Claire Macquet

How Do head coaches brief their athletes? Exploring transformational leadership behaviors in elite team sports

Keywords: Briefing, transformational leadership, coaching, elite sports, teamwork vs. task-work, expertise

How do head coaches brief their athletes? Exploring transformational leadership behaviors in elite team sports

Anne-Claire Macquet, Neville Stanton

The role played by Human Factors and Ergonomics (HFE) in sports and outdoor recreation (SOR) has grown over the last decade, with studies ranging from physical HFE to cognitive HFE and systems HFE [START_REF] Salmon | Human Factors and Ergonomics in Sport and Outdoor Recreation: From individuals and their equipment to complex socio-technical systems and their frailties[END_REF]. HFE in SOR aims to describe and understand the behaviours of individuals, teams, organisations and systems and to optimize them (Salmon, Read, Walker, Stevens, et al., 2020a). It plays an important role in understanding and optimising the performance of athletes and staff, organizations and systems, or injury and accident prevention [START_REF] Salmon | Human Factors and Ergonomics in Sport and Outdoor Recreation: From individuals and their equipment to complex socio-technical systems and their frailties[END_REF]. [START_REF] Salmon | Human Factors methods and Sports Sciences[END_REF] highlighted the lack of crossdisciplinary interaction between HFE and Sports Science. To bridge this gap, a number of HFE researchers looked at cross-disciplinary interaction, investigating HFE concepts such as decision-making and sense-making in sports contexts (e.g., [START_REF] Macquet | Decision-making in sports[END_REF]Macquet & Kragba, 2009). [START_REF] Salmon | Human Factors and Ergonomics in sport[END_REF] demonstrated the need to facilitate cross-disciplinary interactions through the application of HFE concepts to Sports Science, however this interaction can prove valuable in the opposite direction too, with the application of Sports Science concepts to HFE.

HFE in SOR has received less attention in the area of coaching, specifically in briefing and debriefing in elite sports [START_REF] Macquet | Divide and rule: A qualitative analysis of the debriefing process in elite team sports[END_REF]. This could be due to the fact that only a small coaches manage elite teams [START_REF] Macquet | Time management in the context of elite sport training[END_REF]. Coaches and athletes consider the briefing function to be particularly important in order to achieve high performance (e.g., [START_REF] Mesquita | Analysis of content interventions of volleyball coaches in the preparation competitive meeting-Comparative study between coaches of male and female senior teams[END_REF]. Within teams, formal briefings are conducted prior to a mission in order to facilitate communication within and between teams and thereby support teamwork (e.g., Wacker & Kolbe, 2015). Teamwork refers to the interdependent components of performance enabling efficient coordination of the performance of multiple individuals [START_REF] Salas | Is there a "big five" in teamwork?[END_REF]. By way of contrast, taskwork is concerned with the individual components of performance. In HFE, briefing provides information about the mission planning (e.g., [START_REF] Stanton | Distributed Decision-Making in multi helicopter teams[END_REF], enables an understanding of shared mental models of what has to be accomplished by the team members (e.g., Lingard, Reghr, Orser, Reznick et al., 2008) and makes sense of situations in order to develop effective plans [START_REF] Jensen | Sensemaking in military planning: A methodological study of command teams[END_REF].

In terms of HFE, the aims of team briefing in sports psychology can be related to the five core components of the teamwork model developed by [START_REF] Salas | Is there a "big five" in teamwork?[END_REF]: (a) provide information about the game plan (e.g., [START_REF] Lainé | Le discours d'avant-match des entraîneurs de rugby: des temps d'intervention enchâssés[END_REF], relating to mutual performance monitoring; (b) anticipate how to adapt the game plan in light of the changing circumstances (e.g., [START_REF] Mesquita | Analysis of content interventions of volleyball coaches in the preparation competitive meeting-Comparative study between coaches of male and female senior teams[END_REF], relating to adaptability; (c) foster mutual trust among teammates and encourage team cohesion (e.g., [START_REF] Lainé | Le discours d'avant-match des entraîneurs de rugby: des temps d'intervention enchâssés[END_REF][START_REF] Vargas-Tonsing | An exploratory examination of the effects of coaches' pregame speeches on athletes' perceptions of self-efficacy and emotion[END_REF], concerning team orientation; (d) inspire teams, encourage and push players to a higher level of performance (e.g., [START_REF] Vargas-Tonsing | An exploratory examination of the effects of coaches' pregame speeches on athletes' perceptions of self-efficacy and emotion[END_REF], pertaining to team leadership;

and (e) pay attention to athletes' needs and positively influence emotions in a context of high level pre-competition anxiety (e.g., [START_REF] Breakey | Female athletes' perceptions of a coach's speeches[END_REF], relating to backup behaviours.

Briefing in sports has received little empirical research, especially in elite sports. In top level sports, competitions include high stakes, pressure and uncertainty which have possible effects on emotions, attention and fatigue [START_REF] Krane | The mental readiness form as a measure of competitive state anxiety[END_REF]. Studying the briefing process is of particular interest in the context of top level performance because the briefing aims to prepare athletes to adapt to potential situations during competition (e.g., [START_REF] Mesquita | Analysis of content interventions of volleyball coaches in the preparation competitive meeting-Comparative study between coaches of male and female senior teams[END_REF] and relatively little is known about how to brief athletes. To our knowledge, no studies have examined briefing in team sports during major competitions, namely continental and world championships, the Olympic Games and qualifying tournaments. During these competitions, coaches have only a short time to brief athletes. The research described within this paper aims to fill this gap by developing a better understanding of coaches' experience of briefing in elite team sports and facilitating cross-disciplinary interactions between HFE and Sports Science.

Coaches behave like leaders in managing their team (e.g., [START_REF] Smith | Transformational leadership in elite sport: A qualitative analysis of effective leadership behaviours in cricket[END_REF]. [START_REF] Bass | Two decades of research and development in transformational leadership[END_REF] modelled two styles of leadership: transactional and transformational. He showed that transactional leadership is concerned with the interactions between the leader and follower in order to meet their own self-interests. By way of contrast, transformational leadership refers to the leader guiding the follower beyond immediate selfinterest. Transformational leadership relates to team leadership, which is a core component of teamwork [START_REF] Salas | Is there a "big five" in teamwork?[END_REF]. Identifying how HCs behave to promote teamwork at the time they brief their team of elite players is of central interest in this paper.

In elite military settings, [START_REF] Callow | Measurement of transformational leadership and its relationships with team cohesion and performance level[END_REF] developed the Differentiated Transformational Leadership Inventory (DTLI) to explain the specific components of transformational leadership. The DTLI has also been used in sports [START_REF] Smith | Transformational leadership and task cohesion in sport: The mediating role of intrateam communication[END_REF]Smith et al., 2017). This inventory comprises six transformational leadership behaviours: individual consideration (where leaders treat each follower as a respected individual and answer his/her needs); inspirational motivation (where leaders inspire others, develop and share a positive vision of the future); intellectual stimulation (where leaders push followers to solve problems in creative ways and use reasoning before taking action); fostering acceptance for group goals and promoting teamwork (where leaders favour cooperation among followers and promote teamwork to achieve common goals); high performance expectations (where leaders push followers to achieve high goals); appropriate role modelling (where leaders transmit what is really important and a sense of mission); and transactional behaviour concerned with contingent rewards (where leaders reward expected behaviours). Smith et al. (2017) showed that all coaches were transformational leaders to some extent. The most cited behaviours by coaches were high performance expectations and individual consideration. [START_REF] Smith | Transformational leadership and task cohesion in sport: The mediating role of intrateam communication[END_REF] showed that the transformational behaviours concerned with fostering acceptance of group goals and individual consideration affected task cohesion. These results provided interesting insight into transformational leadership behaviours used by coaches in general. They did not however account for the behaviours present during the briefing.

As transformational leadership behaviours have been shown to have a positive effect on individual and group outcomes in sports teams (Smith et al., 2017), it is important to understand the process through which this occurs in order to have a more complete picture of the behaviours used while briefing athletes during major competitions. Athletes need to be positively influenced and motivated to achieve their best and reach top level performances (e.g., [START_REF] Breakey | Female athletes' perceptions of a coach's speeches[END_REF]. Although previous literature from HFE and sports psychology has stressed the aims of briefing (e.g., [START_REF] Vargas-Tonsing | An exploratory examination of the effects of coaches' pregame speeches on athletes' perceptions of self-efficacy and emotion[END_REF] and core components of teamwork [START_REF] Salas | Is there a "big five" in teamwork?[END_REF], no study has investigated the transformational behaviours coaches use while briefing athletes in major competitions to foster teamwork and team performance. By examining the transformational behaviours coaches use when they conduct collective briefings for athletes, this research aims to better understand the briefing process.

To extend our understanding of leadership practices and teamwork and facilitate crossdisciplinary interaction between HFE and Sports Science, this study aims to use transformational leadership as a lens through which to explore HCs' behaviours when HCs briefed a team of athletes several hours or the day before a match during major competitions.

More specifically, the aim of the study was to identify the "how" and "why" of briefing behaviours, establishing which leadership behaviours underpin the briefing process and teamwork in elite team sports.

Method

To develop our understanding of briefing practice in elite sports, qualitative methodology was adopted in this study involving a form of inquiry [START_REF] Smith | Developing rigor in qualitative research: Problems and opportunities with sport and exercise psychology[END_REF]. This approach used semi-structured interviews. Interviews provide in-depth information that accounts for meaningful experience in contextual situations [START_REF] Jones | Research methods for sport studies[END_REF].

They enable rich data to be captured from various perspectives [START_REF] Smith | Developing rigor in qualitative research: Problems and opportunities with sport and exercise psychology[END_REF].

Interviews give the researcher the freedom to explore in depth the participant's experiences within single cases and then place them in a larger framework in order to generalize within cases, as well as to generalize across them [START_REF] Tracy | Qualitative quality: Eight big-tent criteria for excellent qualitative research[END_REF]. In organisational psychology literature and sporting contexts, researchers have conducted interviews to show the behaviours of effective leaders (e.g., Smith et al., 2017) and coaches when they briefed a sports team [START_REF] Lainé | Le discours d'avant-match des entraîneurs de rugby: des temps d'intervention enchâssés[END_REF]. Furthermore, qualitative methods enable the interpretations of different participants to be examined and provide a richer representation of the theoretical construct from various perspectives [START_REF] Peräkylä | Analyzing talk and text[END_REF][START_REF] Sparkes | Qualitative research methods in sports, exercise and health: From process to product[END_REF].

Such a qualitative approach is particularly useful when there is limited access to participants [START_REF] Klein | Seeing what others don't. The remarkable ways we gain insights[END_REF]. In the present study, interviews were used to explore the leadership experience of HCs in order to model HC behaviour during athlete briefings in major competitions.

Participants

Seven male and two female HCs gave written, informed, consent and participated in the study. They were selected based on their position and relevant experience [START_REF] Jones | Research methods for sport studies[END_REF].

The recruitment criterion was to enrol national HCs who worked with sports teams taking part in major competitions (four teams had won medals in the Olympic Games and/or European/world championships).

The first author made initial contact with these HCs to inform them of the purpose of the study and request permission to conduct interviews about their leadership behaviours when they brief players. Participants included HCs of handball, basketball, volleyball and ice and field hockey teams. HCs varied in terms of years of coaching in first division club (M club team = 13.9 years, SD club team = 7.2 years), national team (M national team = 7 years, SD national team = 4.6 years), and gender (two females and seven males). This gender difference reflects a gender equity problem in France; there are very few female national coaches in Olympic sports (Lamberbourg & Paupardin, 2008). This may be an example of the glass ceiling, which limits female access to the position of manager in professional groups (Dubar & Triper, 2005). The study respected the ethics guidelines of the institution in which it took place and those of the French National Centre of Scientific Research and general data protection regulations applicable to research in Europe.

Data Collection

Semi-structured interviews were conducted individually with each HC so that an understanding of the briefing process could be developed. The interviews were conducted during the national team sport off-season period, when HCs were preparing for the following season. An interview guide with three sections was created for this study. Section 1 provided information about the study's aim and the right to withdraw at any time of the study; participants were assured that personally identifiable information about themselves would not be disclosed at any point of the research process. Section 2 consisted of introductory questions (e.g., Would you like to introduce yourself?). These questions allowed the interviewer to develop a rapport with the participant and gain an insight into their background. Section 3 related to the HCs' behaviours when briefing athletes. HCs were asked to explain how they briefed their team under specific circumstances in order to explore experiences in depth within single cases (e.g., How do you start the briefing? What do you say to the athletes to enable them to adapt to the opposing team's game? What information do you present to the athletes? Do you pay attention to athletes while providing information? What do you say to motivate them? Do you encourage athletes to analyse the opposing team's game?). Probing questions were asked to encourage participants to provide more information about relevant issues they had raised (e.g., What do you say to manage athletes' stress when the match stakes are high? What do you say to athletes when the opposing team has a better chance of success than their own team?).

Interviews were led by the lead author, who had already conducted such interviews in previous studies and had coaching and playing experience in team sports. The full interviews, which lasted between 60 and 90 minutes, were recorded and then transcribed. Participants confirmed the accuracy of transcriptions to confirm that the research data was valid (Smith & Mc Gannon, 2017;[START_REF] Tracy | Qualitative quality: Eight big-tent criteria for excellent qualitative research[END_REF].

Data Processing

There were two steps in the processing of the interview data. In the first step, the comparative method was used [START_REF] Corbin | Basics of qualitative research: Grounded theory. Procedures and techniques[END_REF]. This approach addressed the overall purpose of the briefings and led to questions such as: "What's going on?" and "What are they doing when they brief athletes? From these questions, concepts were generated to explain the way in which the behaviours were used. Inductive and deductive analysis were used to generate these concepts. Meaningful units were extracted from the interview transcripts to ascertain what HC behaviours look like in briefing. A meaningful unit is a segment of text providing a single idea. These meaningful units were classified into first-order categories (based on common features) and compared to gain robustness and meaningful coherence [START_REF] Tracy | Qualitative quality: Eight big-tent criteria for excellent qualitative research[END_REF].

Firstly, the first author and a collaborator trained in qualitative processing independently coded the transcribed interviews. The data was constantly compared. No additional data was obtained from the eighth interview, which was a good indication that saturation had occurred [START_REF] Jones | Research methods for sport studies[END_REF]. Then, the first author and collaborator compared the meaningful units (MU) they extracted from the interview transcripts and corresponding firstorder categories these provided. Where disagreements emerged, researchers discussed to find an agreement. Researcher's reflection was used to improve cohesiveness, robustness and appropriateness [START_REF] Jones | Research methods for sport studies[END_REF][START_REF] Smith | Developing rigor in qualitative research: Problems and opportunities with sport and exercise psychology[END_REF]. Moreover, 81.5% reliability was achieved for the identification and categorisation of the meaningful units. This is in line with the desirable threshold of 80% (Von Someren, [START_REF] Von Someren | The think aloud method: A practical guide to modeling cognitive processes[END_REF] and Kappa-type, demonstrating that the agreement meets the requirements of qualitative data analysis [START_REF] Landis | An applied application of hierarchical Kappa-type statistics in the assessment of majority agreement among multiple observers[END_REF]. A total of 471 meaningful units were identified and classified into nine firstorder categories.

Secondly, first-order categories that related to briefing behaviours were coded into or transactional behaviour, namely (g) contingent rewards. For each first-order category, the question "What kind of leadership behaviour does this briefing behaviour relate to?" was asked.

The first author and the collaborator then compared the first-order categories with the dimensions of transformational and transactional leadership until agreement was reached, which occurred for each second-order category. In order to ensure neutrality, objectivity and trustworthiness in the results, category checking was used and participants confirmed the appropriateness of the categorisation of the data to the way they briefed athletes [START_REF] Smith | Developing rigor in qualitative research: Problems and opportunities with sport and exercise psychology[END_REF][START_REF] Tracy | Qualitative quality: Eight big-tent criteria for excellent qualitative research[END_REF].

In the second step, the authors compared the behaviours underpinning the briefing process. More specifically, they compared the frequencies of transformational leadership behaviours, and those of briefing behaviours among HCs, between expert and junior HCs, and male and female HCs.

Results

All HCs reported that they minimised the length of the briefing presentation in order to allow athletes maximum time for concentration. They briefed athletes in a quiet room at the hotel; chairs were oriented toward a screen and a flip chart, like a classroom. Presentations lasted between 20 and 45 min depending on the time available before the match.

Two kind of results emerged from the data processing: (a) transformational behaviours demonstrated in briefing behaviours; and (b) comparison of the frequencies of the behaviours underpinning the briefing process. An overall model of the briefing process is presented in

Transformational behaviours demonstrated in briefing behaviours

Results showed that briefings consisted of nine behaviours related to six transformational behaviours [START_REF] Callow | Measurement of transformational leadership and its relationships with team cohesion and performance level[END_REF] Intellectual stimulation, acceptance of group goals and high performance expectations were used to develop the game plan (i.e., mission planning). Individual consideration and inspirational motivation highlighted the team leadership dimension of teamwork (e.g., [START_REF] Salas | Is there a "big five" in teamwork?[END_REF]. High performance expectations and appropriate role modelling point to the team orientation dimension.

Comparison of the frequencies of the behaviours underpinning the briefing process

Results indicated which leadership behaviours underpinned the briefing process. HCs were shown to exhibit all leadership behaviours apart from appropriate role modelling, and all briefing behaviours except "enable athletes to implement tactics from the briefing" and "adopt attitudes showing positive values" (see Table 2). Fostering acceptance of group goals was the most frequently exhibited transformational behaviour (38% of total behaviours, see Table 1).

Behaviours related to individual consideration and intellectual stimulation were mentioned with similar frequency by all HCs (22% and 18%, see Table 1). HCs were shown to favour briefing behaviours that "presenting athletes with an assessment of the opposing team's game and their own team's plan (29% of total behaviours) and manage athletes' stress and fatigue (22% of total behaviours, see Table 2).

*** insert Table 2 around here***

Discussion

This study is the first of which we are aware to explore transformational leadership in elite team sports during briefing by HCs of their teams in order to stimulate and inspire athletes to achieve positive outcomes. The results obtained in this study reinforce the use of the DTLI [START_REF] Callow | Measurement of transformational leadership and its relationships with team cohesion and performance level[END_REF] and highlight behaviours used by HCs to promote teamwork.

The results are discussed in two parts: (a) consistency with the DTLI and promotion of teamwork; and (b) behaviours underpinning the briefing process.

Consistency of results with the DTLI (Callow et al., 2009) and promotion of teamwork

HCs were shown to manage athletes' stress and fatigue and build confidence when the athletes questioned their own ability, in a context of fatigue and pre-match anxiety. Results suggest that HCs use backup behaviours to take care of athletes and are attentive to their needs and capabilities both during the game and the briefing and inspire confidence. These results are consistent with individual consideration as described within the DTLI (e.g. Smith et al., 2017) and analysis of complex systems in work [START_REF] Hulme | Sports organizations as complex systems: Using cognitive work analysis to identify the factors influencing performance in an elite netball organization[END_REF].

HCs identified stressors for athletes and focused on the problems raised and emotions to enable athletes to cope with stress, which is consistent with coping strategies explained by [START_REF] Lazarus | Stress, appraisal and coping[END_REF] in their model of stress and coping. This suggests that HCs display interpersonal emotional competencies and are able to identify, understand, express, regulate and use the emotions of others. Emotional competencies enable effective teamwork to be developed by establishing a comfortable atmosphere among team members [START_REF] Suwandana | Role of transformational leadership mediation: Effect of emotional and communication intelligence towards teamwork effectiveness[END_REF]. Assessing the profile of emotional competence of HCs could be a worthwhile avenue for research in briefing and teamwork.

During briefing, HCs did not know exactly how the match would go. As the DTLI predicted [START_REF] Callow | Measurement of transformational leadership and its relationships with team cohesion and performance level[END_REF], they spent time developing a vision of the team in which players went beyond self-interest, and did their best to achieve team success according to their roles and capabilities until the very end of the match. These results are in line with the dimensions of team orientation and team leadership in teamwork [START_REF] Salas | Is there a "big five" in teamwork?[END_REF], and results in briefing (e.g., [START_REF] Lainé | Le discours d'avant-match des entraîneurs de rugby: des temps d'intervention enchâssés[END_REF][START_REF] Vargas-Tonsing | An exploratory examination of the effects of coaches' pregame speeches on athletes' perceptions of self-efficacy and emotion[END_REF].

Results demonstrated that HCs encouraged athletes: (a) to analyse opponents' strengths, weaknesses and patterns of coordination, and develop the game plan, and (b) to be flexible and adapt tactics. Encouraging athletes to analyse video sequences suggests that HCs wanted athletes to analyse the opponents' game themselves, identify possible problems, demonstrate initiative, and participate in the decision-making process. This problem-solving approach is consistent with the intellectual stimulation dimension within the DTLI [START_REF] Callow | Measurement of transformational leadership and its relationships with team cohesion and performance level[END_REF]Smith et al., 2017), decision-making and assertiveness [START_REF] Burke | Team task analysis[END_REF], and adaptability [START_REF] Salas | Is there a "big five" in teamwork?[END_REF]. Inviting players to take part in the game analysis, using closed-looped communication and mutual trust (allowing them to admit possible mistakes or areas where they disagree), may help team members to share mental models and thereby improve team performance, in line with results seen in briefing in the field of medicine (Wacker & Kolbe, 2015). To our knowledge, no study on briefing has yet reported on the results of empowering athletes to make their own analysis and be responsible for the game plan. Exploring this strategy could provide a fruitful avenue for future research.

Analysis of the results highlighted the fact that HCs provided athletes with pragmatic perspectives to the problems raised and organised the work to be done. They gave athletes roles. This suggests that HCs aimed to favour explicit coordination, which has been proven to be effective in complex situations (Wacker & Kolbe, 2015), and achieve a common goal, in line with fostering acceptance of group goals [START_REF] Callow | Measurement of transformational leadership and its relationships with team cohesion and performance level[END_REF] and mission planning [START_REF] Stanton | Distributed Decision-Making in multi helicopter teams[END_REF]. Consistent with Mesquita et al.'s (2008) results, HCs provided concise information so that the athletes can remember it, despite the pre-match anxiety; they also shared descriptive information (i.e., opposing team's trends) and prescriptive information (i.e., pattern of coordination to implement). 2009) and coordinating teamwork mechanisms [START_REF] Burke | Team task analysis[END_REF][START_REF] Salas | Is there a "big five" in teamwork?[END_REF]. The training session also enabled implicit and explicit coordination to be encouraged, in line with results observed in team performance in medicine (Wacker & Kolbe, 2015), and contributed to players' empowerment and team spirit.

Results indicated that the

As the DTLI predicts, HCs were shown to set high performance expectations, and maintain high levels of performance and effort in order to win. [START_REF] Hulme | Sports organizations as complex systems: Using cognitive work analysis to identify the factors influencing performance in an elite netball organization[END_REF] stressed the importance of sharing responsibility for performance within the team and the findings of our study support this position.

The results also showed that HCs did not frequently report on role modelling during briefing. Thus our findings do not necessarily support the idea of transmitting a sense of mission as described by [START_REF] Callow | Measurement of transformational leadership and its relationships with team cohesion and performance level[END_REF] and [START_REF] Hulme | Sports organizations as complex systems: Using cognitive work analysis to identify the factors influencing performance in an elite netball organization[END_REF]. Further work involving interviews with the leader and his/her followers, could improve our understanding of the role of mission.

Analysis of these results did not reveal any behaviour relating to the dimension of contingent rewards. It might be expected that this dimension would only be seen in HCs after a match is played, as shown by Macquet et al. (2015). Studying such behaviours could be a worthwhile avenue for future research.

Leadership behaviours underpinning the briefing process

The results showed that HCs displayed all dimensions of transformational leadership, apart from appropriate role modelling, and favoured fostering acceptance of group goals and individual consideration. They suggest that HCs focused on the task to be completed and the individual completing the task, in line with studies on task-work and teamwork (e.g., [START_REF] Annett | Editorial Team-work -a problem for ergonomics[END_REF]. They support the notion that different leadership and briefing behaviours are used in different ways. The findings show the multifaceted nature of briefings in elite sports and complementarity of behaviours in favouring teamwork. They also show that the transformational leadership behaviours used by HCs while briefing are not limited to the team leadership dimension described in teamwork (e.g., [START_REF] Salas | Is there a "big five" in teamwork?[END_REF].

The results of the present study present some similarities and differences with Macquet et al.'s (2015) study on debriefing in elite team sports. During both briefing and debriefing, HCs were shown to display transformational leadership and teamwork, consisting of individual consideration, intellectual stimulation and decision-making, mission planning, tactics implementation from the briefing/debriefing during a training session. In briefing, the current results also highlight that HCs motivated athletes, set high performance expectations and provided appropriate role modelling. In debriefing, previous results revealed that HCs acknowledged athletes' work and rewards (i.e., transactional leadership), suggesting that transactional leadership may be used solely in debriefing. Previous and current results also suggest that briefing and debriefing refer to a continual process and future research is warranted to examine leadership behaviours while briefing and debriefing in different contexts.

From an applied perspective, it would be interesting to develop workshop facilitators to enable HCs to analyse their own leadership behaviours. This could encourage HCs to introduce specific leadership and briefing behaviours, to engage in behaviour-change techniques such as behavioural practice (i.e., role-playing as a coach or player in briefing situations to use their newly-acquired behaviours), and to give feedback (e.g., group discussion about the when and how to display appropriate leadership behaviours while briefing a team). For more details, please see [START_REF] Lawrason | A transformational coaching workshop for changing youth sport coaches' behaviours: A pilot intervention study[END_REF].

This study presents certain limitations. Firstly, it did not compare the findings of the interviews with the HCs with the views of athletes and staff. Inclusion of interviews with athletes and staff could provide additional information. Secondly, it did not compare the findings with those from other HCs. Briefing has received little empirical research, specifically in elite sports, and sports psychology research has often involved few participants because of the small number of coaches that manage elite teams [START_REF] Macquet | Time management in the context of elite sport training[END_REF]. Thirdly, the current study, which was exploratory, did not cover the effects of number of each behaviour on the team performance. Studying such effects could open up other possibilities for future research.

Conclusion

This study facilitates cross-disciplinary interactions between HFE and Sports Science and furthers understanding of the behaviour of expert HCs. It shows that HCs are transformational leaders who promote teamwork and task-work as ways to achieve team performance and athletes' well-being. The findings show the multifaceted nature of briefings in elite sports. They highlight the importance of pushing players to achieve high performances as well as supporting players emotionally and providing tactical guidance. The results reinforce the DTLI [START_REF] Callow | Measurement of transformational leadership and its relationships with team cohesion and performance level[END_REF] and teamwork models [START_REF] Salas | Is there a "big five" in teamwork?[END_REF][START_REF] Burke | Team task analysis[END_REF]. Although traditional teamwork studies are useful and should continue to be used, this study provides evidence that exploring leadership behaviours can also contribute insights into ways to improve team performance. Further study of briefing, leadership and teamwork are encouraged in sports and other contexts. Before playing Russia, we noticed that the players were stressed. We thought they needed to gain self-confidence. We showed them positive video sequences from difficult parts of the game during their match against Spain, in order to show them that they are able to achieve positive outcomes in difficult situations. We wanted to make them feel more confident". HC9 Inspirational motivation

Making athletes want to surpass themselves

Relates to communication in order to foster players' motivation, inspire a positive vision of the future, incite players to achieve their best performance, and establish a positive atmosphere "Before the final, I told them they were the best team I had ever managed. I said: You've worked a lot. You've made progress. You've done your job, now you can go a long way in the OG…". HC5 Intellectual stimulation Encouraging players to analyse the opponent's game and develop their own game plan Includes communication and stimulation of players to analyse opponents' strengths, weaknesses and patterns of coordination, prioritizing tasks, setting goals and developing the game plan; and encouraging players to solve problems in a creative way and use reasoning before taking action, as well as fostering assertiveness "We showed them video sequences of the opponents and pushed them to communicate and analyse the game. We asked them to analyse specific patterns of players' coordination. Then, we asked them what they thought they should do to adapt."HC8 Pushing players to be flexible Refers to preparing players to adapt to unexpected internal or external changes under pressure and adjust tactics if they prove to be ineffective during a game "How will you play if the ball comes from that side?". HC9

Fostering acceptance of group goals

Presenting players with an assessment of the opposing team's game and their own team's plan Includes developing a common understanding of the opponent's game (strengths, weaknesses and most effective pattern of coordination); presenting appropriate tactics to achieve common goals, prioritizing goals and setting a game plan; providing concise information so that athletes can retain it; ensuring they share mental models of game plans "we provide them information of opponents team tactics that can disrupt own team and how to adapt" HC6 Providing players with roles Refers to providing players with specific roles and setting out what each player is expected to do (i.e., task-work), distributing the workload among teammates using accurate knowledge of their skills and responsibilities (i.e., teamwork)

"We provided the setter and other players with information so that everyone knew what could happen and what they were required to do". HC3 Enabling players to implement tactics from the briefing Concerns anticipating and predicting teammates' needs in order to implement tactics and, during training sessions, ensuring that players are able to carry them out and monitor teammate performance; encouraging players to ask questions, comment and adapt "During a short training session, we applied what we had said during the briefing, in order to ensure they had fully understood which tactics to implement, when and how. We pushed them to communicate with teammates to carry out the game plan". HC7 High performance expectations Improving skills, the level of the game and maintaining efforts Includes maintaining effort throughout a match, and improving the level of the game to reach top-level performance and win medals, maintaining belief in the importance of teams goals over the goals of individual teammates "Before playing Brazil, I told them that this team was very efficient. We won't catch up with them. Nevertheless, we can be as efficient as them in that respect. Consequently, the score will be close and we can win." HC3 Appropriate role modelling

Adopting attitudes showing positive values

Refers to transmitting positive attitudes, values, and sense of mission to players "It was important to start the Olympic Games, to find the right rhythm and then to progress. We aimed to display our concentration and conscientious attitude."HC1

  second-order categories according to the classification scheme of the DTLI. Each behaviour was categorised within either the dimensions of transformational behaviour, namely (a) individual consideration; (b) inspirational motivation; (c) intellectual stimulation; (d) fostering acceptance for group goals; (e) high performance expectations; (f) appropriate role modelling;

Fig

  Fig.1.

  HCs enabled athletes to implement tactics from the briefing during a training session. Training session provided the opportunity to use backup behaviours to anticipate and adapt to players' needs and used close loop communication to ensure players shared mental models about what needed to be implemented and how to collaborate, in line with Callow et al.'s results (

Figure

  Figure Legend: Figure 1. The Briefing Model

Table Caption Table 1 .

 Caption1 Framework of Briefing Behaviours

	Transformational	Briefing behaviours	Definition	Illustration
	dimension
	Individual	Managing players' stress	Includes taking players' needs into account in a context of high stakes for
	consideration	and fatigue	teams and countries, treating each athlete as a respected individual, managing
			athletes' stress and fatigue by building confidence and taking limited
			attention into account

(40%)

(1%)

Data availability statement

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.


Kh Khazen

H J Von Bardeleben

S A Zargaleh

Jean-Louis L Cantin

Mu Zhao

Weibo Gao

T Biktagirov

U Gerstmann

High

published or not. The documents may come

I. INTRODUCTION

The implementation of various quantum technology proofof-concepts based on atomlike defect centers in silicon carbide have attracted much attention in the past few years. Whereas the NV -center in diamond seems to be the favorite choice for such applications [START_REF] Awschalom | Quantum technologies with optically interfaced solid-state spins[END_REF], the material properties of diamond are not optimal for large-scale integration, and recently silicon carbide (SiC) has been proposed as an interesting alternative, due to its mature microelectronic properties [START_REF] Weber | Quantum computing with defects[END_REF][START_REF] Weber | Defects in SiC for quantum computing[END_REF][START_REF] Dzurak | Quantum computing: Diamond and silicon converge[END_REF][START_REF] Boretti | Optical materials: Silicon carbide's quantum aspects[END_REF][START_REF] Gordon | Defects as qubits in 3C-and 4H-SiC[END_REF][START_REF] Economou | Spin photon entanglement interfaces in silicon carbide defect centers[END_REF][START_REF] Castelletto | Silicon carbide for novel quantum technology devices[END_REF]. Since then, an intense research effort focusing on three vacancy related intrinsic defects in SiC has confirmed these predictions: they are the negatively charged silicon monovacancy (V Si ), the neutral silicon-carbon divacancies (V Si V C ), and the negatively charged NV centers (N C V Si ) . Their basic properties, such as the polytype dependence of their optical and spin properties [START_REF] Falk | Polytype control of spin qubits in silicon carbide[END_REF], their spin coherence times [START_REF] Christle | Isolated electron spins in silicon carbide with millisecond coherence times[END_REF][START_REF] Simin | Locking of electron spin coherence above 20 ms in natural silicon carbide[END_REF], and the influence of neighboring nuclear spins [START_REF] Yang | Electron spin decoherence in silicon carbide nuclear spin bath[END_REF][START_REF] Falk | Optical Polarization of Nuclear Spins in Silicon Carbide[END_REF][START_REF] Seo | Quantum decoherence dynamics of divacancy spins in silicon carbide[END_REF][START_REF] Simin | Long-lived quantum memory in silicon carbide with natural isotope abundance[END_REF], have been the object of the earlier studies. Room temperature coherent control has been demonstrated by various authors [START_REF] Koehl | Room temperature coherent control of defect spin qubits in silicon carbide[END_REF][START_REF] Soltamov | Room Temperature Coherent Spin Alignment of Silicon Vacancies in 4H and 6H-SiC[END_REF][START_REF] Widmann | Coherent control of single spins in silicon carbide at room temperature[END_REF][START_REF] Carter | Spin coherence and echo modulation of the silicon vacancy in 4H-SiC at room temperature[END_REF]. Room temperature quantum entanglement has been achieved for the PL6 center in 4H-SiC [START_REF] Klimov | Quantum entanglement at ambient conditions in a macroscopic solid-state spin ensemble[END_REF]. Magnetic field sensing and thermometry at a nanoscale has been demonstrated for the V Si center [START_REF] Kraus | Magnetic field and temperature sensing with atomic-scale spin defects in silicon carbide[END_REF][START_REF] Zhou | Self Protected Nanoscale Thermometry Based on Spin Defects in Silicon Carbide[END_REF]. Enhancing the optical properties by embedding these defects in photonic cavities has been shown [START_REF] Radulaski | Photonic crystal cavities in cubic (3C) polytype silicon carbide films[END_REF][START_REF] Calusine | Cavity-Enhanced Measurements of Defect Spins in Silicon Carbide[END_REF] as well as the tuning of their spin properties by electric fields [START_REF] Klimov | Electrically Driven Spin Resonance in Silicon Carbide Color Centers[END_REF][START_REF] De Las Casas | Stark tuning and electrical charge state control of single divacancies in silicon carbide[END_REF]. Single photon emission has been shown for defects in different SiC polytypes [START_REF] Lohrmann | A review on single photon sources in silicon carbide[END_REF][START_REF] Wang | Bright room temperature single photon source at telecom range in cubic silicon carbide[END_REF]. These major achievements make intrinsic defects in SiC interesting competitors to the NV -center in diamond [START_REF] Doherty | The nitrogen vacancy colour center in diamond[END_REF].

We have shown recently [START_REF] Von Bardeleben | Identification and magneto-optical properties of the NV center in 4H-SiC[END_REF][START_REF] Von Bardeleben | NV centers in 3C, 4H, and 6H silicon carbide: A novel platform for solid-state qubits and nanosensors[END_REF][START_REF] Von Bardeleben | NV centers in silicon carbide: From theoretical predictions to experimental observation[END_REF][START_REF] Csóré | Characterization and formation of NV centers in 3C, 4H, and 6H-SiC: An ab initio study[END_REF][START_REF] Zargaleh | Nitrogen vacancy center in cubic silicon carbide: A promising qubit in the 1.5 μm spectral range for photonic quantum networks[END_REF][START_REF] Zargaleh | Electron paramagnetic resonance tagged high-resolution excitation spectroscopy of NV-centers in 4H-SiC[END_REF] that also the direct analog of the NV -center in diamond, the NV -centers in SiC, can be generated in all three main polytypes 3C, 4H, 6H of SiC. In SiC the NV center is a silicon vacancy nitrogen nearest neighbor pair with structural similarity to the case of diamond. The identification of the NV -centers in SiC was based on EPR studies, combined with ab initio calculations of their spin Hamiltonian parameters [START_REF] Von Bardeleben | Identification and magneto-optical properties of the NV center in 4H-SiC[END_REF][START_REF] Von Bardeleben | NV centers in 3C, 4H, and 6H silicon carbide: A novel platform for solid-state qubits and nanosensors[END_REF]. In the hexagonal polytypes, due to the lower symmetry of the crystal, different NV center configurations coexist: four (4H) and six (6H) distinct NV, respectively. Like the original NV center in diamond, all the NV centers in SiC have in their 1-charge state a similar electronic structure with a 3 A 2 ground state and 3 E excited state, both with spin S = 1. Most important, they also present an intermediate singlet state, which allows an optical induced spin polarization of the ground state. However, their optical properties are shifted from the visible in diamond into the near infrared (NIR), making them more suitable for transmission in fibers, a further advantage for applications. In contrast to intrinsic defects like divacancies, both well localized single NV centers and spatially controlled arrays of NV centers can be generated in SiC by nitrogen implantation [START_REF] Sato | Formation of nitrogen vacancy centers in 4H-SiC and their near infrared photoluminescence properties[END_REF]. Moreover, the possibility of electrical excitation of NV centers due to the semiconducting properties of SiC is a further advantage of SiC over diamond.

Ab initio calculations of the electronic properties have shown that NV centers in SiC are stable in several charge states. Their charge state is thus related to the Fermi-level position, a parameter, which has to be controlled just as for the NV center in diamond. In n-type material with a Fermi level pinned on the nitrogen shallow donor, the NV centers in 6H-SiC will be in the wrong 2-charge state, but partial electrical compensation or applying reverse bias in space charge regions will favor the interesting 1-charge state. The case of NV centers in 3C polytype is more favorable, as due to its smaller band gap the 2-charge state is not stable and the desired 1charge state of the NV center is already obtained in n-type conducting material [START_REF] Csóré | Characterization and formation of NV centers in 3C, 4H, and 6H-SiC: An ab initio study[END_REF].

Most of the previous studies on color centers in SiC were based on low temperature optical spectroscopy where narrow ZPL were resolved and the spin coherence times of milliseconds were observed [START_REF] Christle | Isolated electron spins in silicon carbide with millisecond coherence times[END_REF]. Extension to room temperature spectroscopy has nevertheless been obtained for two centers, called PL5 and PL6, which have similar electronic properties to the divacancy centers. However, the microscopic structure of the PL5, PL6 centers is still unknown. It is clear, however, that they are not simple divacancies in the 4H polytype as often tacitly assumed [START_REF] Klimov | Quantum entanglement at ambient conditions in a macroscopic solid-state spin ensemble[END_REF]. They have been detected as native defects in semi-insulating bulk 4H-SiC but as their microscopic structure is unknown; they cannot be purposely generated up to now and they have not been related to irradiation treatments. There has been the proposition that they might be related to 6H polytype inclusions in 4H bulk samples. Thus, NV centers in the 6H polytype might present certain advantages. The demonstration of room-temperature entanglement of the PL6 center in 4H-SiC [START_REF] Klimov | Quantum entanglement at ambient conditions in a macroscopic solid-state spin ensemble[END_REF] is an additional motivation for their study.

In this work, using EPR-tagged high resolution excitation spectroscopy (EPR-RES), we demonstrate the possibility to address selectively the different NV -centers in 6H-SiC using the very narrow intracenter transitions 3 A→ 3 E , which can be monitored via EPR due to the related optically induced ground state spin polarization. DFT calculation of the zerofield splitting parameters (D, E) allow us to attribute the paramagnetic NV centers to specific defect configurations and EPR-RES spectroscopy to associate with the ZPL lines. The attribution is further confirmed by the direct calculation of the vertical excitation energies. These measurements have to be done at low temperature in order to observe the narrow zero phonon lines with high intensity. However, coherent control of NV -centers in 4H-SiC have also been demonstrated at room temperature [START_REF] Wang | Coherent control of nitrogen vacancy center spins in silicon carbide at room temperature[END_REF].

II. COMPUTATIONAL METHODS

First-principles calculations were performed in the framework of density functional theory (DFT) using the QUANTUM ESPRESSO package [START_REF] Giannozzi | QUAN-TUM ESPRESSO: A modular and open-source software project for quantum simulations of materials[END_REF][START_REF] Giannozzi | Advanced capabilities for materials modeling with Quantum ESPRESSO[END_REF]. Exchange-correlation effects of the electronic system have been described with the semilocal Perdew-Burke-Ernzerhof (PBE) functional [START_REF] Perdew | Generalized Gradient Approximation Made Simple[END_REF], projectoraugmented wave (PAW) pseudopotentials [START_REF] Blöchl | Projector augmented-wave method[END_REF]. The axial and basal configuration of the negatively charged NV pairs have been modeled with periodic boundary conditions using symmetric 324-and 648-atom supercells of hexagonal shape. Based on fully relaxed ground-state geometries (forces below 0.01 eV/A) we calculated the full magnetic signature of the spin-triplet state of the N C V Si -pairs. To obtain accurate FIG. 1. Crystal structure of 6H-SiC showing the three nonequivalent Si and C (black circles) lattice sites, hexagonal (h) and quasicubic (k1 and k2), whereby k1 is always neighboring one k2 and three h sites (k2 has quasicubic neighbors exclusively). Thus we obtain the following NV center configurations: basal: hk1, k2k2, k1h and axial: hh, k2k1, k1k2 (for further details see the text). As an example we show also the magnetization density of the basal (k2k2, left) and the axial (k1k2, right) NV pair providing C 1h and C 3v symmetry, respectively.

estimates for the g tensors, hyperfine (HF) splittings, as well as the D and E value of the zero-field splitting (ZFS), we used scalar relativistic, norm-conserving gauge-including (GI) PAW pseudopotentials. In the calculations of the ZFS parameters the effects of the spin-orbit interaction has also been considered providing rather small contributions below 60 MHz (<4%) to the dominating spin-spin part. The spinspin part is due to dipole-dipole interaction of the two-particle density [START_REF] Biktagirov | Calculation of spin-spin zero-field splitting within periodic boundary conditions: Towards all-electron accuracy[END_REF] and tends to be overestimated by the so-called spin contamination [START_REF] Jost | Why spin contamination is a major problem in the calculation of spin-spin coupling in triplet biradicals[END_REF], a spurious kind of antiferromagnetic spin polarization. In order to provide reasonable estimates for D, E allowing a better comparison with the experimental data, we correct the D SS tensors for this effect [START_REF] Biktagirov | Efficient scheme to eliminate spin contamination in magnetic dipolar coupling: Application to the zero-field splitting of NVcenters[END_REF]. For the calculation of the vertical excitation energies (ZPL absorption) we apply the same procedure used in [START_REF] Zargaleh | Electron paramagnetic resonance tagged high-resolution excitation spectroscopy of NV-centers in 4H-SiC[END_REF] for the NV centers in 4H-SiC. Convergence of the EPR parameters as well as of the vertical excitation energies are obtained for 3 × 3 × 3 k-point sampling and a plane-wave basis set with 680 eV energy cutoff.

In Fig. 1 we show the 6H polytype crystal structure with the indication of the three distinct lattice sites labeled h, k1, k2 corresponding to the hexagonal and two quasicubic sites, respectively. Note that k1 is always neighboring an h site, independent of the atomic occupation of the respective sublattice (see Fig. 1). The labeling is important as it allows us to distinguish and to classify the six different NV center configurations, which can be obtained by N occupying a carbon lattice site and being associated with a nearest neighbor silicon vacancy. The notation k1k2, e.g., corresponds to N on a k1 site (carbon sublattice) and the Si vacancy on the neighboring k2 site (Si sublattice). Thus, the three axial and three basal NV centers correspond to the following combinations: axial hh, k2k1, k1k2 and basal hk1, k2k2, k1h. It should be noted, however, that in some previous publications [START_REF] Csóré | Characterization and formation of NV centers in 3C, 4H, and 6H-SiC: An ab initio study[END_REF][START_REF] Davidsson | Identification of divacancy and silicon vacancy qubits in 6H-SiC[END_REF] these labels have been used in a slightly different way (k1 and k2 interchanged for the C sublattice exclusively). For the sake of simplicity, if citing the respective labels are translated into the notation used throughout the present paper [START_REF]Label translation due to interchanged k1/k2 for the C sublattice: The three axial NV centers labeled hh, k1k1, k2k2 in Refs[END_REF].

III. EXPERIMENTAL DETAILS

6H-SiC nitrogen doped bulk samples have been commercially purchased from different suppliers. Typical thickness is 400 μm and the typical sample size 5 × 5 mm 2 . NV centers are not native defects in such material and we introduced them in the classical procedure of high energy particle irradiation followed by a thermal annealing step. We irradiated the samples at room temperature with high energy (2 to 12 MeV) electrons or protons, which due to elastic collisions and electronic excitation will form silicon and carbon vacancies and interstitials. Typical fluences are 10 15 to10 17 particles /cm 2 . In a second step, the samples were annealed at 900

• C to initiate the diffusion of the Si vacancies, which are mobile in this temperature range, and will form complexes with the doping related N centers, which are stable at this temperature. The NV center concentration is thus controlled by the N doping level. In parallel to the NV centers, divacancy centers will also be formed due to the presence of carbon vacancies equally generated by the irradiation process.

The EPR measurements have been performed with a Bruker X-band spectrometer under standard conditions with 100 kHz field modulation. Whereas the NV centers can be observed in the whole temperature range from T = 300 to 4 K the optical excitation measurements have all been performed at T = 4 K. To selectively excite the NV centers, we have used a tunable infrared single mode laser with a tuning range from 1170 to 1260 nm, a wavelength precision of 0.05 nm, and a maximum power of 30 mW. The linewidth was computer controlled and had been calibrated with a wavemeter.

The photoluminescence measurements were performed on the same samples at T = 10 K using nonresonant excitation of a 1000 nm diode laser beam, which was focused on the sample through a 0.5 Na microscope objective. The emitted photons were then dispersed by a 0.5 m focal lens monochromator and detected with an InGaAs diode.

IV. EXPERIMENTAL RESULTS

Figure 2 presents the wide range photoluminescence PL spectrum from 1050 to 1350 nm of an irradiated and annealed bulk sample. In the shorter wavelength range (1050-1150 nm), the previously reported zero phonon lines (ZPL) Q1-Q5 [START_REF] Falk | Polytype control of spin qubits in silicon carbide[END_REF] are observed (Table I). They had not been identified initially as the PL and ODMR data alone allowing us only to determine the symmetry of the associated defects (axial/basal) but not their microscopic structure. Later, they have been tentatively associated with the negatively charged divacancies (V Si V C ) based on the comparison with EPR results, which give additional information on the microscopic structure of the defects, when combined with theory to interpret the spin Hamiltonian parameters. The association of these ZPL with the divacancy centers seems now to be fairly well established [START_REF] Davidsson | Identification of divacancy and silicon vacancy qubits in 6H-SiC[END_REF]. In the higher wavelength range, five new ZPL labeled NV1-NV5 are observed, which, as we will show, are associated with the N C V Si -centers. Higher resolution measurements show the NV2 ZPL to be a doublet ( NV2a,b). The energy of these ZPL is in good agreement with the range FIG. 2. High-resolution photoluminescence spectrum of 6H-SiC displaying under nonresonant excitation the ZPL of the VV°and NV -centers; T = 10 K, optical excitation at 1000 nm. On the left (smaller wavelength), the PL corresponding to the divacancy centers are shown in the small (blue) rectangular frame; on the right (for larger wavelength) the NV center PL peaks are framed by the larger (red) rectangle. We observe five ZPL as two ZPL (NV2a/NV2b) are nearly degenerate at 1183 nm and not resolved in this PL spectrum. This is also the case for the VV°ZPL where two ZPL QL5/QL6 are nearly degenerate. FIG. 3. X-band EPR spectrum for B//c and T = 4 K displaying the six doublet spectra of the three axial and three basal spin S = 1 NV -centers (see also Fig. 1). Basal spectra can be easily identified: due to their off-axis orientation, their resonance fields are very different for the orientation of B//c. 0.96 to 1.00 eV, predicted by previous ab initio calculations [START_REF] Von Bardeleben | Identification and magneto-optical properties of the NV center in 4H-SiC[END_REF][START_REF] Von Bardeleben | NV centers in 3C, 4H, and 6H silicon carbide: A novel platform for solid-state qubits and nanosensors[END_REF][START_REF] Von Bardeleben | NV centers in silicon carbide: From theoretical predictions to experimental observation[END_REF][START_REF] Csóré | Characterization and formation of NV centers in 3C, 4H, and 6H-SiC: An ab initio study[END_REF][START_REF] Zargaleh | Nitrogen vacancy center in cubic silicon carbide: A promising qubit in the 1.5 μm spectral range for photonic quantum networks[END_REF][START_REF] Zargaleh | Electron paramagnetic resonance tagged high-resolution excitation spectroscopy of NV-centers in 4H-SiC[END_REF].

The same samples studied by photoluminescence have been investigated by EPR spectroscopy. In Fig. 3 we show a large-scale EPR spectrum for the orientation of the applied magnetic field B//c which is taken under optical excitation in order to increase the EPR signal intensity. For an excitation with 980 nm, it displays predominantly the six NV - centers. Due to their different spin Hamiltonian parameters, they give rise to six distinct doublet spectra, corresponding to the ms = 0 → +1 and ms = 0 → -1 magnetic dipole transitions of each spin S = 1 center. The axial and basal NV centers can be directly distinguished for this orientation of the applied magnetic field as they provide clearly different splittings (Fig. 3). The use of the nonresonant 980 nm optical excitation allows us to display all six centers simultaneously. The optical excitation increases the EPR signal intensity from its thermal equilibrium value due to the optically induced ground state spin polarization induced by the recombination process from the excited 3 E state. Therefore, the phases of the low-field and high-field EPR transitions are inverted, and we observe the low-field lines in absorption and the highfield lines in emission. To extract the corresponding spin Hamiltonian parameters, given in Table II, we measured for each center the angular variation of the resonance fields as shown in Fig. 4(a). As in the case of the NV centers in 3C and 4H-SiC, the superhyperfine (SHF) interaction with the 14 N atom (nuclear spin I = 1) of the NV center is directly resolved in the EPR spectra for both the axial and basal centers [Fig. 4(b)]. The resulting triplet structure [Figs. 4(c) and 4(d)] presents a fingerprint of the NV centers and allows an easy distinction from the divacancy centers, which have almost the same spin distribution [START_REF] Von Bardeleben | Identification and magneto-optical properties of the NV center in 4H-SiC[END_REF] and thus similar spin Hamiltonian parameters, but of course no 14 N SHF, thus resulting in a single central line EPR spectrum.

The experimental ZFS parameters of the NV -centers, obtained by an angular variation of the EPR spectra for a rotation in the [START_REF] Riedel | Resonant Addressing and Manipulation of Silicon Vacancy Qubits in Silicon Carbide[END_REF][START_REF] Falk | Polytype control of spin qubits in silicon carbide[END_REF][START_REF] Radulaski | Photonic crystal cavities in cubic (3C) polytype silicon carbide films[END_REF][START_REF] Yang | Electron spin decoherence in silicon carbide nuclear spin bath[END_REF][START_REF] Kraus | Magnetic field and temperature sensing with atomic-scale spin defects in silicon carbide[END_REF][START_REF] Christle | Isolated electron spins in silicon carbide with millisecond coherence times[END_REF][START_REF] Falk | Optical Polarization of Nuclear Spins in Silicon Carbide[END_REF][START_REF] Widmann | Coherent control of single spins in silicon carbide at room temperature[END_REF][START_REF] Klimov | Electrically Driven Spin Resonance in Silicon Carbide Color Centers[END_REF][START_REF] Zwier | All-optical coherent population trapping with defect spin ensembles in silicon carbide[END_REF] and (1100) planes, are presented in Table II. They are compared to the predicted values from first-principle calculations (see Sec. II).The assignment of the six NV -centers to the specific microscopic configuration is based on the comparison with the calculated and measured zero-field splitting parameters (D,E) and the SHF interaction with the 14 N nuclei. We see that the calculated ZFS parameters D, even though being systematically 3%-5% lower than the values measured at T = 4 K, reproduce well the experimental values and thus allow their assignment. This assignment will be further confirmed, as explained below, by the agreement between the calculated and experimental ZPL energies.

The electronic spins of the NV centers [as is the case of the divacancy (VV) centers] are mainly localized on the three nearest neighbor carbon atoms of the Si vacancy [see also Fig. 1(a)]; they give rise to the central HF interaction. The natural abundance of the 13 C isotope is small (1.1%) but the central hyperfine interaction could be resolved for the strongest NV -center (k2k1) [Fig. 4(b)]. The corresponding splitting of 51 MHz for B//c is in agreement with the theoretical predictions (see Table II and Ref. [START_REF] Von Bardeleben | NV centers in 3C, 4H, and 6H silicon carbide: A novel platform for solid-state qubits and nanosensors[END_REF]). Superhyperfine (SHF) interactions of about 10 MHz with 29 Si nuclei are also visible [see, e.g., blue spectrum in Fig. 4(b)]. Like the g tensor these Si-related hyperfine interactions are basically identical for all six NV -centers (see also Ref. [START_REF] Von Bardeleben | NV centers in 3C, 4H, and 6H silicon carbide: A novel platform for solid-state qubits and nanosensors[END_REF]) and will not be discussed in more detail here.

Previously, it has been shown that nuclear spins can play a major role as safe storage units of quantum information (quantum memories), whose interaction with the electronic spins (qubits) form a complete package (spinbus) for quantum information processing [START_REF] Widmann | Coherent control of single spins in silicon carbide at room temperature[END_REF]. The superhyperfine interactions

FIG. 4. EPR spectra of the NV -centers at T = 4 K under nonresonant displaying the six NV -centers. (a) Angular variation of the six NV centers for a rotation of the magnetic field from B//c to B// [START_REF] Riedel | Resonant Addressing and Manipulation of Silicon Vacancy Qubits in Silicon Carbide[END_REF][START_REF] Falk | Polytype control of spin qubits in silicon carbide[END_REF][START_REF] Radulaski | Photonic crystal cavities in cubic (3C) polytype silicon carbide films[END_REF][START_REF] Yang | Electron spin decoherence in silicon carbide nuclear spin bath[END_REF][START_REF] Kraus | Magnetic field and temperature sensing with atomic-scale spin defects in silicon carbide[END_REF][START_REF] Christle | Isolated electron spins in silicon carbide with millisecond coherence times[END_REF][START_REF] Falk | Optical Polarization of Nuclear Spins in Silicon Carbide[END_REF][START_REF] Widmann | Coherent control of single spins in silicon carbide at room temperature[END_REF][START_REF] Klimov | Electrically Driven Spin Resonance in Silicon Carbide Color Centers[END_REF][START_REF] Zwier | All-optical coherent population trapping with defect spin ensembles in silicon carbide[END_REF], allowing the determination of the spin Hamiltonian parameters compiled in Table II. (b) For the highest-intensity axial NV center (k2k1) the central hyperfine interaction with one 13 C nucleus (one of the three C neighbors) is resolved (blue); (red line): spectrum multiplied by 200. (c) Higher resolution EPR spectrum of the axial NV center (k1k2) displaying directly the SHF interaction with nuclear spin I = 1 of the 14 N neighbor. (d) EPR spectrum of the hk1 basal NV center showing a strongly reduced SHF with 14 N as compared to the other NV centers.

have a very particular configuration for the case NV centers in 6H-SiC (e.g., compared to diamond), as the higher spatial distance between the interacting sites prevents strong interactions, which would disturb the information stored on the nuclear spins. The values, both experimental and theoretical, of the 14 N hyperfine interaction parameters and the CHF interactions with the three C neighbors are shown in Table II.

Time resolved EPR measurements under optical excitation allow us also to investigate the spin-lattice relaxation times. We have measured the decline of the ground-state spin polarization after cutoff of the optical excitation for the six NV -centers at T = 4 K. The measured transient behavior of the polarization can be simulated with a single exponential decay function characterized by a time constant t 1 . The results, shown in Figs. 5(a) and 5(b), indicate exceptionally long spin lattice times T 1 of their ground state of the order of several seconds. These measurements were done on an ensemble of NV -centers, thus the T 1 times of individual NV -centers can be expected to be even longer. The spin relaxation times, which are longer than those of the divacancy centers, make NV -centers extremely attractive candidates for quantum technology (QT) applications. More information on the spin coherence times require time resolved ODMR measurements with pulsed (optical, microwave) sequences and single defect spectroscopy.

A. Qubit addressing

The assignment of each ZPL line to a specific NV -center is crucial to leverage the selectivity of optical addressing of a particular defect center as a qubit. This is, however, not achievable using only photoluminescence spectroscopy. Pre- viously, the assignment based only on theoretical predictions of the ZPL emission energies has shown its limit, due to the challenges in an accurate description of the Jahn-Teller distorted excited state [START_REF] Thiering | Ab initio calculation of spin-orbit coupling for an NV center in diamond exhibiting dynamic Jahn-Teller effect[END_REF] and, by this, still too high relative uncertainties in earlier calculations [START_REF] Von Bardeleben | Identification and magneto-optical properties of the NV center in 4H-SiC[END_REF][START_REF] Von Bardeleben | NV centers in 3C, 4H, and 6H silicon carbide: A novel platform for solid-state qubits and nanosensors[END_REF][START_REF] Von Bardeleben | NV centers in silicon carbide: From theoretical predictions to experimental observation[END_REF][START_REF] Csóré | Characterization and formation of NV centers in 3C, 4H, and 6H-SiC: An ab initio study[END_REF]. Moreover, as the range of the ZPL energies of the different NV defects is small as compared to the LO phonon energies, resonant PL excitation measurements with a detection via the phonon side bands will result in the mixing of phonon sidebands, destroying reliable readout processes. However, resonant optical excitation of the NV centers in their zero-phonon line and detection via EPR enables selective addressing of the specific center and allows us to overcome this problem. In parallel, it facilitates a theoretical treatment [START_REF] Zargaleh | Electron paramagnetic resonance tagged high-resolution excitation spectroscopy of NV-centers in 4H-SiC[END_REF] as the excitation energies are not affected by Franck-Condon shifts.

The resonant excitation EPR measurements were performed on the low-field line of each NV -center (Fig. 2). We measured the EPR signal intensity of each center while scanning the excitation wavelength over the different ZPL lines. We had already reported in our previous studies of NV centers in 4H-SiC [START_REF] Zargaleh | Electron paramagnetic resonance tagged high-resolution excitation spectroscopy of NV-centers in 4H-SiC[END_REF] that the optical excitation, which monitors the absorption ZPL line of the 3 A→ 3 E intracenter transition, is resonant with the ZPL emission line. We observe the same result for the NV -centers in the 6H polytype. This is different from the case of the NV -center in diamond for which a Stokes shift of 200 meV has been observed [START_REF] Batalov | Low Temperature Studies of the Excited State Structure of Negatively Charged Nitrogen-Vacancy Color Centers in Diamond[END_REF]. The intensity of the EPR signal is measured as a function of the laser wavelength, which is scanned in steps of 0.05 nm. The results are shown in Fig. 6 and Table III.

The wavelength scanning (cf. Fig. 6) demonstrates (i) the absorption ZPL are resonant with the emission ZPL lines and (ii) the absorption ZPL lines are very sharp with a half-width of only 0.2 to 0.3 nm. This difference in linewidth between emission and absorption ZPL lines is due to the mixing of the excitation and emission beams in PL experiments, resulting in extrinsic broadening of the peaks. In Table III we compare the measured ZPL wavelengths with the calculated ones.

B. Defect assignment

The comparison of the ZPL PL spectra and the photo-EPR excitation spectra demonstrate that both agree in wavelength and thus allow us to assign the ZPL to each specific NV - center (Fig. The A further element comforting the assignment is the consideration of the rhombic ZFS parameter E, which shows large differences in the three basal cases and is at least qualitatively reproduced in our calculations. In particular, we found that the center with medium D value (k2k2) shows the largest rhombicity E (cf. Table II).

V. CONCLUSION

The EPR-tagged high-resolution photoexcitation spectroscopy [START_REF] Zargaleh | Nitrogen vacancy center in cubic silicon carbide: A promising qubit in the 1.5 μm spectral range for photonic quantum networks[END_REF] based on the intracenter recombination induced ground state spin polarization has allowed us to associate the photoluminescence ZPL with the specific microscopic configurations of the axial and basal NV -centers. The assignment of the paramagnetic NV -centers is based on their spin Hamil-FIG. 7. Superposition of the photoluminescence ZPL (black line) and the absorption ZPL lines (color lines) as determined by highresolution resonant excitation of the EPR spectra. The nearly degenerate ZPL of the axial (hh) and basal (k1h) NV -centers are not resolved in the PL spectrum due to insufficient resolution. tonian parameters, which have been obtained from ab initio calculations. Advanced calculations of the zero-field splitting parameter D, taking into account the spin contamination, have allowed us to further increase the accuracy with which the values can be obtained. As in the case of NV -centers in 4H-SiC we observe a negligible Franck-Condon shift between the emission and absorption ZPL of the intracenter transition 3 E → 3 A 2 . With their long spin coherence times and their optical spectral range of 1.2 μm the NV centers in 6H-SiC should be promising candidates for QT applications.

FIG. 5 .

 5 FIG. 5. (a), left: Transient behavior of the EPR signal of the axial k2k1 NV -center after switch-off of the optical excitation at t = 20 s; T = 4 K, circles experiment, blue line fit with a single exponential decay. (b), right: Time constants of the relaxation time of the optically induced ground state spin polarization of the six NV - centers; T = 4 K.

FIG. 6 .

 6 FIG. 6. (a)-(e)Resonant excitation EPR spectra measured (at T = 4 K) individually for each NV -center on its low field EPR line. These spectra correspond to the ZPL absorption lines of the NV centers; the ZPL expected at 1155 nm is out of range of the tunable NIR laser but can be attributed from the knowledge of the other five ZPL lines.

  (a)], the trends are very well reproduced and we assign them according to these results. Note that by this assignment the trend in the vertical excitation energies is also well reproduced [see Fig.8(b)].

FIG. 8 .

 8 FIG. 8. (a), left: Comparison of experimental and calculated ZFS parameters D for the NV -centers. (b), right: Comparison of the experimental and DFT-calculated absorption vertical ZPL wavelength of the six NV -centers. As expected the PBE-calculated excitation energies are systematically underestimated by about 100 meV, but the trend is correctly reproduced.

TABLE I .

 I Photoluminescence ZPL lines of the six VV°and six NV -centers in 6H-SiC. As in the case of VV°(QL5/QL6), the ZPL lines of two of the NV -centers (NV2a/NV2b) are degenerate [see Fig.1(b)]; thus, only five ZPL are resolved. For further assignment of the NV emission, see also TableIII.

	Label		VV 0 ZPL emission (nm)	Symmetry/	NV ZPL emission (nm)	Label
	V Si -V C	Expt. [12]	Theory [51]	orientation	Expt. (thiswork)	N C -V Si
	QL1	1139	1320	axial	1227.3	NV4
	QL2	1135	1329	axial	1182.6	NV2a
	QL6	1093	1308	axial	1155	NV1
	QL3	1124	1313	basal	1242	NV5
	QL4	1108	1290	basal	1204	NV3
	QL5	1093	1275	basal	1183	NV2b

TABLE II .

 II Spin Hamiltonian parameters (experimental and DFT calculated) of the six NV -centers in 6H-SiC: zero-field splitting parameters D,E, hyperfine splitting A for the (SHF) interaction with14 N, and central hyperfine interaction parameter A //c ( 13 C). All values are in MHz; experimental data given for T = 4 K.

	NV	ZFS expt	ZFS DFT	HF expt	HF DFT	HF expt	HF DFT
	center	D,E	D ,E	|A|( 14 N) expt	A( 14 N) DFT	A //c ( 13 C) expt	A //c ( 13 C) DFT
	hh	1340	1298	1.32	-1.08	-	65.3 (3×)
	k 2 k 1	1289	1266	1.21	-1.12	51	58.1 (3×)
	k 1 k 2	1367	1324	1.02	-1.02	-	66.8 (3×)
	k 2 k 2	1321/138	1259/144	1.00	-0.86	-	116.9/74.1 (2×)
	k 1 h	1346/∼20	1280/10	1.00	-0.96	-	130.0/69.1 (2×)
	hk 1	1247/∼20	1187/21	0.67	-0.59	-	128.5/65.5 (2×)

TABLE III .

 III Comparison of the ZPL lines in emission and absorption (experiment and DFT theory) and their assignment to the particular axial or basal NV center configuration deduced from the EPR spin Hamiltonian parameters. centers was based on the EPR parameters. The point symmetry C 3v or C 1h allows us a direct distinction between axial and basal NV centers; the site assignment (k1, k2, h) of each axial and basal NV -center is based on theory predictions of their ZFS parameters and additionally confirmed by their calculated ZPL energies. Even though the absolute values of the calculated ZFS parameters are slightly lower than the experimental ones [cf. TableIIand Fig.8

		ZPL absorption	ZPL absorption	ZPL emission	ZPL absorption	Configuration
	ZPL label	(nm), expt.	linewidth (nm)	(nm), expt.	(nm), DFT	(from EPR)
	NV4 axial	1227.26	0.3	1227	1307	k 2 k 1 axial
	NV1 axial	-	-	1155	1244	k 1 k 2 axial
	NV2a axial	1182.62	0.2	1183	1284	hh axial
	NV5 basal	1242.4	0.2	1242	1324	hk 1 basal
	NV3 basal	1204.0	0.2	1204	1327	k 2 k 2 basal
	NV2b basal	1183.2	0.2	1183	1286	k 1 h basal
	of the NV

ACKNOWLEDGMENTS S.A.Z. wishes to acknowledge the support from the Merlion Grant France-Singapore and the Quantum Nanopho-tonic Laboratories at Nanyang Technical University. U.G. and T.B. acknowledge support from the Deutsche Forschungsgemeinschaft via priority program SPP 1601 (GE-1260/5-2).