Etienne Lorchat

Luis E Parra López

Cédric Robert

Delphine Lagarde

Guillaume Froehlicher

Takashi Taniguchi

Kenji Watanabe

Xavier Marie

Stéphane Berciaud
email: stephane.berciaud@ipcms.unistra.fr

S B Wrote

Filtering the photoluminescence spectra of atomically thin semiconductors with graphene

Atomically thin semiconductors made from transition metal dichalcogenides (TMDs) are model systems for investigations of strong light-matter interactions and applications in nanophotonics, opto-electronics and valley-tronics. However, the photoluminescence spectra of TMD monolayers display a large number of features that are particularly challenging to decipher. On a practical level, monochromatic TMD-based emitters would be beneficial for low-dimensional devices but this challenge is yet to be resolved. Here, we show that graphene, directly stacked onto TMD monolayers enables single and narrow-line photoluminescence arising solely from TMD neutral excitons. This filtering effect stems from complete neutralization of the TMD by graphene combined with selective non-radiative transfer of long-lived excitonic species to graphene. Our approach is applied to four tungsten and molybdenum-based TMDs and establishes TMD/graphene heterostructures as a unique set of opto-electronic building blocks, suitable for electroluminescent systems emitting visible and near-infrared photons at near THz rate with linewidths approaching the lifetime limit.

TMD monolayers (thereafter simply denoted TMD), such as MoS 2 , MoSe 2 , WS 2 , WSe 2 are direct-bandgap semiconductors [START_REF] Mak | Atomically Thin MoS2: A New Direct-Gap Semiconductor[END_REF][START_REF] Splendiani | Emerging Photoluminescence in Monolayer MoS2[END_REF], featuring short Bohr radii, large exciton binding energy of hundreds of meV [START_REF] Wang | Colloquium: Excitons in atomically thin transition metal dichalcogenides[END_REF][START_REF] Goryca | Revealing exciton masses and dielectric properties of monolayer semiconductors with high magnetic fields[END_REF] and picosecond excitonic radiative lifetimes at low temperature [START_REF] Palummo | Exciton radiative lifetimes in twodimensional transition metal dichalcogenides[END_REF][START_REF] Robert | Exciton radiative lifetime in transition metal dichalcogenide monolayers[END_REF][START_REF] Fang | Control of the exciton radiative lifetime in van der waals heterostructures[END_REF], all arising from their strong 2D Coulomb interactions, reduced dielectric screening and large effective masses [START_REF] Wang | Colloquium: Excitons in atomically thin transition metal dichalcogenides[END_REF][START_REF] Goryca | Revealing exciton masses and dielectric properties of monolayer semiconductors with high magnetic fields[END_REF]. Since the first investigations of light emission from TMDs, it has been clear that their lowtemperature spectra is composed of at least two prominent features, stemming from bright neutral excitons (X 0 ) and charged excitons (trions, X ) [START_REF] Mak | Tightly bound trions in monolayer mos2[END_REF][START_REF] Ross | Electrical control of neutral and charged excitons in a monolayer semiconductor[END_REF][START_REF] Courtade | Charged excitons in monolayer WSe2: Experiment and theory[END_REF] endowed with a binding energy of typically 20 to 40 meV relative to X 0 . Among the vast family of TMDs, one may distinguish between so-called dark and bright materials [START_REF] Echeverry | Splitting between bright and dark excitons in transition metal dichalcogenide monolayers[END_REF]. In the case of Tungsten-based TMDs, a spindark state lies lower than X 0 . Conversely, in Molybdenum based-TMDs, X 0 lies below (MoSe 2 ) or very near (MoS 2 ) the spin-dark state, resulting in brighter emission at low temperature. As a result, X 0 and X emission dominate the PL spectrum of Mo-based TMDs [START_REF] Ross | Electrical control of neutral and charged excitons in a monolayer semiconductor[END_REF], whereas the emission spectra of W-based TMDs display a complex series of lines stemming from X 0 , biexcitons (XX 0 ) [START_REF] Barbone | Charge-tuneable biexciton complexes in monolayer WSe2[END_REF][START_REF] Ye | Efficient generation of neutral and charged biexcitons in encapsulated wse 2 monolayers[END_REF][START_REF] Paur | Electroluminescence from multiparticle exciton complexes in transition metal dichalcogenide semiconductors[END_REF][START_REF] Li | Revealing the biexciton and trion-exciton complexes in bn encapsulatedWSe2[END_REF], charged excitonic states (including X [START_REF] Courtade | Charged excitons in monolayer WSe2: Experiment and theory[END_REF][START_REF] Vaclavkova | Singlet and triplet trions in WS2 monolayer encapsulated in hexagonal boron nitride[END_REF] and charged biexcitons (XX ) [START_REF] Barbone | Charge-tuneable biexciton complexes in monolayer WSe2[END_REF][START_REF] Ye | Efficient generation of neutral and charged biexcitons in encapsulated wse 2 monolayers[END_REF][START_REF] Paur | Electroluminescence from multiparticle exciton complexes in transition metal dichalcogenide semiconductors[END_REF][START_REF] Li | Revealing the biexciton and trion-exciton complexes in bn encapsulatedWSe2[END_REF]), spin-dark excitons [START_REF] Robert | Fine structure and lifetime of dark excitons in transition metal dichalcogenide monolayers[END_REF][START_REF] Zhou | Probing dark excitons in atomically thin semiconduc-tors via near-field coupling to surface plasmon polaritons[END_REF][START_REF] Zhang | Magnetic brightening and control of dark excitons in monolayer WSe2[END_REF], defect-induced emission and exciton-phonon sidebands [START_REF] Lindlau | The role of momentum-dark excitons in the elementary optical response of bilayer wse 2[END_REF][START_REF] Liu | Valley-selective chiral phonon replicas of dark excitons and trions in monolayer WSe2[END_REF].

Considerable progress has been made to deterministically observe intrinsic TMD emission features. In particular, encapsulation of TMDs in hexagonal boron nitride (BN) films results in narrower neutral exciton linewidth [START_REF] Cadiz | Excitonic linewidth approaching the homogeneous limit in MoS2-based van der waals heterostructures[END_REF][START_REF] Obafunso A Ajayi | Approaching the intrinsic photoluminescence linewidth in transition metal dichalcogenide monolayers[END_REF], approaching the radiative limit [START_REF] Fang | Control of the exciton radiative lifetime in van der waals heterostructures[END_REF][START_REF] Scuri | Large excitonic reflectivity of monolayer mose2 encapsulated in hexagonal boron nitride[END_REF][START_REF] Back | Realization of an electrically tunable narrow-bandwidth atomically thin mirror using monolayer mose2[END_REF], without however, getting rid of the other emission features mentioned above. Even in electrostatically gated devices tuned near the charge neutrality point, sizeable emission sidebands remain observable at energies close to the X feature, suggesting residual charge inhomogeneity [START_REF] Ross | Electrical control of neutral and charged excitons in a monolayer semiconductor[END_REF][START_REF] Courtade | Charged excitons in monolayer WSe2: Experiment and theory[END_REF] or intrinsic contributions from longer-lived exciton-phonon replicas [START_REF] Lindlau | The role of momentum-dark excitons in the elementary optical response of bilayer wse 2[END_REF][START_REF] Liu | Valley-selective chiral phonon replicas of dark excitons and trions in monolayer WSe2[END_REF].

The complex emission spectra of TMD stimulate lively scientific debates. Conversely, obtaining atomically-thin semiconductors with single, narrow emission lines remains an important challenge in the field. An appealing solution could consist in interfacing a TMD monolayer with graphene. Indeed, the semi-metallic character of graphene and its highly symmetric electronic structure [START_REF] Castro Neto | The electronic properties of graphene[END_REF], with its Dirac point lying within the bandgap of Mo-and W-based TMD [START_REF] Wilson | Determination of band offsets, hybridization, and exciton binding in 2D semiconductor heterostructures[END_REF], makes it an ideal electron and hole acceptor, through static charge transfer [START_REF] Hill | Exciton broadening in WS2/graphene heterostructures[END_REF][START_REF] Froehlicher | Charge versus energy transfer in atomically thin graphene-transition metal dichalcogenide van der waals heterostructures[END_REF]. Unfortunately, at room temperature, the effective X 0 lifetime is in the ns range [START_REF] Palummo | Exciton radiative lifetimes in twodimensional transition metal dichalcogenides[END_REF][START_REF] Robert | Exciton radiative lifetime in transition metal dichalcogenide monolayers[END_REF][START_REF] Froehlicher | Charge versus energy transfer in atomically thin graphene-transition metal dichalcogenide van der waals heterostructures[END_REF] and interlayer coupling between TMDs and graphene results in significant PL quenching [START_REF] Froehlicher | Charge versus energy transfer in atomically thin graphene-transition metal dichalcogenide van der waals heterostructures[END_REF][START_REF] He | Electron transfer and coupling in graphene-tungsten disulfide van der Waals heterostructures[END_REF][START_REF] Yuan | Photocarrier generation from interlayer chargetransfer transitions in WS2-graphene heterostructures[END_REF] due to picosecond energy transfer mediated by either charge tunneling (Dexter-type) or longer-range dipole-dipole interaction (Förster-type) [START_REF] Froehlicher | Charge versus energy transfer in atomically thin graphene-transition metal dichalcogenide van der waals heterostructures[END_REF][START_REF] Selig | Theory of optically induced Förster coupling in van der Waals coupled heterostructures[END_REF][START_REF] Basko | Förster energy transfer from a semiconductor quantum well to an organic material overlayer[END_REF]. However, a much more favorable situation may occur at lower temperatures (typically, below 100 K), where the radiative lifetime of X 0 drastically shortens [START_REF] Palummo | Exciton radiative lifetimes in twodimensional transition metal dichalcogenides[END_REF][START_REF] Robert | Exciton radiative lifetime in transition metal dichalcogenide monolayers[END_REF] and becomes of the same order of magnitude as the theoretically estimated energy transfer time [START_REF] Selig | Theory of optically induced Förster coupling in van der Waals coupled heterostructures[END_REF].

In this work, we demonstrate that W-and Mo-based TMDs coupled to a graphene monolayer exhibit only one single and narrow emission line that is assigned to X 0 radiative recombination, indicating complete neutrality. The short-lived X 0 states are minimally affected by non-radiative transfer to graphene and subsequent PL quenching, in stark contrast with longerlived excitonic species, which are massively quenched. Graphene has been recognised as a partner material of choice to improve the opto-electronic response of TMDs [START_REF] Massicotte | Picosecond photoresponse in van der Waals heterostructures[END_REF], whereas TMDs hold promise to improve spin transport in graphene [START_REF] Kelly Luo | Optovalleytronic spin injection in monolayer MoS2/few-layer graphene hybrid spin valves[END_REF][START_REF] Avsar | Optospintronics in graphene via proximity coupling[END_REF]. Our results now establish TMD/graphene heterostructures as an outstanding light-emitting system readily interfaced with a quasitransparent conductive channel.

Bright, single-line emission in TMD/graphene heterostructures

Figure 1 shows the PL spectra of van der Waals heterostructures made from monolayers of MoS 2 , MoSe 2 , WS 2 and WSe 2 stacked onto graphene monolayers and encapsulated in BN (lower panel). These spectra are compared to those of neighbouring BN-capped TMD regions (upper panel). All TMD/graphene spectra display one single and narrow Lorentzian emission line, with a full width at half maximum (FWHM) of typically 5 meV, suggesting minimal dephasing and disorder (see supplementary Section 1 for the fitting parameters and Section 2 for MoSe 2 /graphene samples with PL linewidths approaching the lieftime limit). The TMD references also display narrow emission features assigned to X 0 (see asterisks in Fig. 1, upper panel), but the latter are accompanied with the lower energy emission lines introduced above [START_REF] Wang | Colloquium: Excitons in atomically thin transition metal dichalcogenides[END_REF][START_REF] Vaclavkova | Singlet and triplet trions in WS2 monolayer encapsulated in hexagonal boron nitride[END_REF][START_REF] Liu | Valley-selective chiral phonon replicas of dark excitons and trions in monolayer WSe2[END_REF][START_REF] Cadiz | Excitonic linewidth approaching the homogeneous limit in MoS2-based van der waals heterostructures[END_REF] (see supplementary Section 3 for their assignments). The sharp PL lines in TMD/graphene are slightly redshifted (by ∼ 10 meV) with respect to X 0 in the TMD references. By measuring the temperature dependent PL spectra and the differential reflectance (DR) spectra of TMD and TMD/graphene, we can unambiguously assign these single lines to X 0 (see Fig. 2 and supplementary Section 4). Therefore, we conclude (i) that no X emission is measured in TMD/graphene and (ii) that the X 0 redshift in TMD/graphene arises from dielectric screening [START_REF] Froehlicher | Charge versus energy transfer in atomically thin graphene-transition metal dichalcogenide van der waals heterostructures[END_REF][START_REF] Raja | Coulomb engineering of the bandgap and excitons in two-dimensional materials[END_REF]. Crucially, we note that PL quenching of the X 0 line is moderate, systematically of less than one order of magnitude in all samples under study (see Fig. 1 and supplementary Section 1). The difference between PL from TMD and TMD/graphene heterostructures is particularly striking in the case of tungsten-based TMDs. In these dark materials, hot luminescence from X 0 is quite inefficient and lower lying emission lines dominate the PL spectra, especially in WS 2 , (see Fig. 1 and supplementary Section 3). As discussed below, all these features are much longer lived than X 0 in TMD [START_REF] Robert | Exciton radiative lifetime in transition metal dichalcogenide monolayers[END_REF][START_REF] Robert | Fine structure and lifetime of dark excitons in transition metal dichalcogenide monolayers[END_REF][START_REF] Lagarde | Carrier and polarization dynamics in monolayer MoS2[END_REF][START_REF] Nagler | Zeeman splitting and inverted polarization of biexciton emission in monolayer WS2[END_REF] and are thus literally washed out in the emission spectra of TMD/graphene heterostructures due to fast nonradiative transfer to graphene.

Complete TMD neutralization

We now focus on the case of MoSe 2 /graphene heterostructures, with PL mapping, as well as typical DR and PL spectra shown in Fig. 2 for a BN-capped sample deposited onto a glass coverslip. The PL spectrum of BN-capped MoSe 2 is composed of two lines with similar intensities, shifted by 28 meV. The high and lowenergy line are assigned to X 0 and X PL [START_REF] Ross | Electrical control of neutral and charged excitons in a monolayer semiconductor[END_REF], respectively. An X absorption feature emerges on the DR spectrum, with an amplitude considerably smaller than that of the X 0 DR feature (Fig. 2e). In contrast, the BN-capped MoSe 2 /graphene region of the sample displays only X 0 absorption and emission features. As shown in Fig. 2bd, these observations can be consistently made over the whole (> 40 µm 2 ) area of a coupled MoSe 2 /graphene region. This is an important point, since TMD-based van der Waals heterostructures are known to be spatially inhomogeneous and hence, the observation of "trion-free" spectra might be accidental. In return, the absence of X emission can be exploited as a reliable probe of the coupling between TMD and graphene.

We assign the absence of X absorption and emission features in TMD/graphene to the transfer of all the native dopants in the TMD (either electrons or holes, with a typical density on the order of 10 11 -10 12 cm -2 ) to graphene. Such static charge transfer leads to a slight increase of the Fermi level of graphene (typically by less than 100 meV) and to the observation of intrinsic absorp-tion and emission. Alternate scenarii, involving residual doping in the TMD but massive quenching of X formation and/or radiative recombination can safely be ruled out (see supplementary Section 5.1). TMD neutralization is corroborated by room temperature Raman scattering [START_REF] Froehlicher | Charge versus energy transfer in atomically thin graphene-transition metal dichalcogenide van der waals heterostructures[END_REF] and PL measurements (see supplementary Section 5.2).

Photostability and dielectric screening

To further establish the benefits of coupling TMD to graphene, we show, in Fig. 3, the PL spectra of the BNcapped MoSe 2 /graphene introduced in Fig. 2 recorded under continuous wave (cw) photon fluxes (hereafter denoted Φ ph ) at 2.33 eV, spanning more than five orders of magnitude, from 1×10 18 cm -2 s -1 to 3×10 23 cm -2 s -1 , i.e., ≈ 1 mW/µm 2 . Assuming an absorptance of ∼ 10 % at 2.33 eV [START_REF] Li | Measurement of the optical dielectric function of monolayer transition-metal dichalcogenides: MoS2, MoSe2, WS2, and WSe2[END_REF] and an excitonic lifetime of 2 ps in BNcapped MoSe 2 /graphene (see Fig. 4,5), we may estimate injected hot exciton densities ranging from 2 × 10 5 cm -2 up to 6 × 10 10 cm -2 . The X 0 PL intensity scales quasilinearly with Φ ph . We note, however, the emergence of two faint PL features. The first one is asymmetric, blueshifted by about 120 meV from X 0 and its intensity scales linearly with Φ ph . We assign this feature to hot luminescence from the neutral excited X 0 2s excitons (at ∆ 1s-2s = 110 meV) and X 0 3s excitons (at ∆ 1s-3s = 127 meV). The exciton binding energy is E b = 231 meV in BN-capped MoSe 2 , with ∆ 1s-2s ≈ 168 meV. Assuming for simplicity that E b scales proportionally to ∆ 1s-2s , we estimate that the presence of a graphene layer reduces E b down to ≈ 148 meV (see supplementary Section 6). The second feature is redshifted by about 25±2 meV, i.e.,

F Ph (x10 23 cm -2 s -1 ) (b) Dependence of the integrated intensity of the neutral 1s exciton (X 0 brown), sum of the first and second excited neutral excitons X 0 2s and X 0 3s (orange) and photoinduced trion (X , green). The solid lines are fits based on a power law and the critical exponents β are indicated. (c) PL spectrum recorded at Φ ph = 3 × 10 23 cm -2 s -1 showing the X 0 and X features on a linear scale. The X 0 2s and X 0 3s features are shown in the lower inset, where the red line is a double-Lorentzian fit to the data, with the X 0 2s and X 0 3s features individually shown with dashed grey lines. The upper inset in (c) shows the energy difference between X 0 and X as a function of Φ ph .

F Ph (cm -2 s -1 ) X 0 b = 1.0 b = 1.1 X 0 X 0 2s + X 0
a few meV less than the X line in MoSe 2 (see Fig. 2c) and its intensity rises quadratically with Φ ph . Therefore, this feature could tentatively be assigned to a biexciton (XX 0 ). However, XX 0 have recently been observed in MoSe 2 [START_REF] Hao | Neutral and charged inter-valley biexcitons in monolayer mose2[END_REF] and WSe 2 [START_REF] Barbone | Charge-tuneable biexciton complexes in monolayer WSe2[END_REF][START_REF] Ye | Efficient generation of neutral and charged biexcitons in encapsulated wse 2 monolayers[END_REF][START_REF] Paur | Electroluminescence from multiparticle exciton complexes in transition metal dichalcogenide semiconductors[END_REF][START_REF] Li | Revealing the biexciton and trion-exciton complexes in bn encapsulatedWSe2[END_REF] monolayers and display binding energies of 20 meV, significantly lower than the value observed here in a system that undergoes more screening due to the presence of graphene. Thus, the lower energy feature is tentatively assigned to emission from photocreated trions with a slightly reduced binding energy. As previously reported in other low-dimensional materials (e.g.; carbon nanotubes [START_REF] Yuma | Biexciton, single carrier, and trion generation dynamics in single-walled carbon nanotubes[END_REF]), at sufficiently large exciton densities, bimolecular exciton-exciton annihilation (EEA [START_REF] Mouri | Nonlinear photoluminescence in atomically thin layered WSe2 arising from diffusion-assisted exciton-exciton annihilation[END_REF]) can create free carriers. Subsequent photon absorption leads to X formation and emission. In this scenario, a quadratic scaling with Φ ph is expected. Noteworthy, X 0 emission remains more than one order of magnitude brighter than X emission at the highest Φ ph employed here, which justifies why we do not observe a sub-linear rise of the X 0 PL intensity due to EEA. The data in Fig. 3 also reveals the outstanding photostability of TMD/graphene systems that can sustain photon fluxes above typical PL non-linearity and damage thresholds in bare TMD [START_REF] Cadiz | Ultra-low power threshold for laser induced changes in optical properties of 2D molybdenum dichalcogenides[END_REF], without significant photo-induced heating (see supplementary Sections 5 and 7).

Exciton dynamics and exciton transfer time

Let us finally consider exciton dynamics in TMD/graphene. Fig. 4 compares the time-resolved PL (TRPL) of MoSe 2 and MoSe 2 /graphene, recorded at 14 K on another sample deposited on SiO 2 and excited below the X 0 2s state. As shown in Fig. 4a, the filtering effect evidenced in BN-capped TMD/graphene (Fig. 1) also appears prominently samples supported by a rougher SiO 2 substrate (see also supplementary Section 2). A three-level system [START_REF] Fang | Control of the exciton radiative lifetime in van der waals heterostructures[END_REF] considering hot excitons X h , such as finite momentum 1s and possibly 2s excitons, formed shortly after laser excitation [START_REF] Steinleitner | Direct observation of ultrafast exciton formation in a monolayer of WSe2[END_REF], X 0 (i.e., cold 1s excitons with center of mass momentum within the light cone) and the ground state is shown in the inset of Fig. 4a. As the PL rise time lies below our time resolution for all measurements on this sample, the TRPL traces in Fig. 4 are simply fit by the convolution of the instrument response function (IRF) with an exponential decay. In keeping with previous reports, the X 0 exciton lifetime (τ X 0 ) is only ≈ 2.3 ps in bare MoSe 2 , and can be assigned to the radiative lifetime τ rad X 0 [START_REF] Robert | Exciton radiative lifetime in transition metal dichalcogenide monolayers[END_REF], whereas X display a much longer lifetime τ X = 30 ps. Remarkably, within experimental accuracy, τ X 0 has identical values in MoSe 2 /graphene and in the neighbouring MoSe 2 region. This striking result suggests that τ 0 G , the non-radiative transfer time of cold excitons (X 0 ) to graphene, is longer than 2 ps. Let us note, that τ rad X 0 scales as E -2 b and is thus expected to be longer in MoSe 2 /graphene than in the nearby MoSe 2 reference. Hence, observing similar τ X 0 in Fig. 4b,c may be coincidental and result from the compensation between the increase of τ rad X 0 in MoSe 2 /graphene and non-radiative transfer of X 0 to graphene with an estimated timescale τ 0 G ∼ 5 ps (see supplementary Section 8.1). As a result, the X 0 emission yield (defined here as the number of emitted photons divided by the number of cold X 0 ) that is near unity in the bare MoSe 2 monolayer [START_REF] Fang | Control of the exciton radiative lifetime in van der waals heterostructures[END_REF] remains high, near 50 % in MoSe 2 /graphene (see supplementary The right inset shows the data on a semi-logarithmic scale. The grey-shaded area highlights a low-energy PL tail from localised (L) states in bare-MoSe2 that is massively quenched in MoSe2/graphene. A three-level system is shown on the left inset. The blue wavy arrow indicates the exciting laser pump pulse that generates a population of hot excitons (X h ). The latter relax with a lifetime τ rel to form cold excitons (X 0 ), from which radiative recombination occurs with a lifetime τ rad X 0 . The presence of graphene induces non-radiative decay of X h and X 0 with timescales τ h G and τ 0 G , respectively. A similar sketch may be drawn for X and other excitonic sates. Time-resolved PL of the neutral exciton feature (X 0 ) in MoSe2/graphene (b), and in bare MoSe2 (c). The longer-lived tail in the bare MoSe2 PL decay is attributed to exciton localisation. (d) TRPL of the trion feature (X ) in MoSe2. All data were recorded at 14 K in the linear regime under excitation with ps laser pulses at 1.76 eV. The thin solid lines are mono-exponential fits to the data after convolution with the instrument response function (IRF, grey area). The extracted X 0 and X lifetimes (τ X 0 and τX , respectively) are indicated.

Section 8.2).

Still, while the integrated PL intensity from X 0 in MoSe 2 /graphene on SiO 2 is nearly twice that of a closelying MoSe 2 reference (see Fig. 4a), the total PL intensity from MoSe 2 remains ≈ 4.5 times larger than that of MoSe 2 /graphene. Following generation of X h , one may form X 0 , X and localised excitons (e.g., near defects) in bare MoSe 2 . Localised excitons contribute a low-energy tail to the PL spectra, as shown in Fig. 4a (shaded area under the blue trace). Conversely, only X 0 and localised excitons can be formed in neutral graphene/MoSe 2 /SiO 2 , which is consitent with the observed enhancement of X 0 emission. Since localised excitons have long lifetimes [START_REF] Lagarde | Carrier and polarization dynamics in monolayer MoS2[END_REF], their emission is quenched by graphene, as evidenced in Fig. 4a (red trace). The sizeable quenching of the total PL intensity can tentatively be assigned to fast transfer of X h to graphene on a time scale τ h G (see inset in Fig. 4a) that is shorter than τ rel , the relaxation time of X h down to the light cone. This scenario is consistent with the fact that the Förster-type energy transfer time of TMD excitons to graphene is expected to be maximal for zero momentum excitons (i.e., here X 0 ) and to decrease with exciton momentum [START_REF] Selig | Theory of optically induced Förster coupling in van der Waals coupled heterostructures[END_REF][START_REF] Basko | Förster energy transfer from a semiconductor quantum well to an organic material overlayer[END_REF]. All in all, our results strongly suggest that graphene open up efficient non-radiative decay pathways that moderately quench X 0 radiative recombination but instead significantly inhibit X 0 formation. Along these lines, we expect that X 0 formation should be more efficiently inhibited in BN-capped samples, where τ rel is much longer than in SiO 2 supported samples and can be experimentally resolved [START_REF] Fang | Control of the exciton radiative lifetime in van der waals heterostructures[END_REF].

Efficient hot exciton transfer to graphene

In Fig. 5, we investigate exciton dynamics the BNcapped sample discussed in Fig. 123, following pulsed optical excitation slightly below the X 0 2s exciton energy. Importantly, this sample is deposited on a glass coverslip and therefore immune from the cavity effects discussed in ref. [START_REF] Fang | Control of the exciton radiative lifetime in van der waals heterostructures[END_REF]. As introduced in Fig. 123, X 0 PL is quenched in MoSe 2 /graphene, in contrast with the case of the SiO 2 supported sample, where X 0 PL enhance- ment is observed (Fig. 4a). This difference readily suggests that X 0 formation is more efficiently quenched in BN-capped TMD/graphene. The TRPL traces are fit by solving the rate equations associated with the threelevel system introduced in Fig. 4a, with two characteristic times for X h relaxation towards X 0 (or X ) formation and X 0 (or X ) decay, respectively. The short and long times correspond to the rise and decay times in the TRPL measurement, respectively [START_REF] Fang | Control of the exciton radiative lifetime in van der waals heterostructures[END_REF]. Fig. 5b,c reveals that the PL rise time (∼ 1.5 ps) is too close to our resolution limit to be accurately resolved in BNcapped MoSe 2 /graphene and is 2.4 ps in the BN-capped MoSe 2 reference. The PL decay times are ≈ 2.2 ps in MoSe 2 /graphene and ≈ 5 ps in the MoSe 2 reference region, respectively. Interestingly, the ≈ 5.1 ps PL rise time of the long-lived X feature (τ X = 62 ps) in BNcapped MoSe 2 is closely matching the X 0 decay time. We therefore assign this ≈ 5 ps time to τ rel , the relaxation time of X h down to the X and X 0 states in BNcapped MoSe 2 . Hot exciton transfer results in a shortened X h relaxation time τ rel 1.5 ps in BN-capped MoSe 2 /graphene. Finally, the X 0 lifetimes τ X 0 in BNcapped MoSe 2 and MoSe 2 /graphene are assigned to the rise and decay time of their respective TRPL traces and are nearly identical (≈ 2.4 ps and ≈ 2.2 ps, respectively). With these values, following the same reasoning as for the SiO 2 -supported MoSe 2 /graphene sample discussed in Fig. 4, we can estimate that the X 0 emission yield is also near 50 % (see supplementary Section 8.2), demonstrating that non-radiative X 0 transfer has similar efficiencies in BN-capped and SiO 2 -supported MoSe 2 /graphene heterostructures. We conclude that a significant part of X 0 PL quenching is due to efficient non-radiative transfer of X h enabled by graphene and that X 0 PL quenching is more efficient in BN-capped Mose 2 /graphene than SiO 2 /MoSe 2 /graphene due to slower X h relaxation (or equivalently X 0 formation) in BN-capped MoSe 2 .

Conclusions and outlook

In closing, we have shown that graphene neutralizes atomically-thin TMDs, leading to the absence of light emission from charged excitonic species. Graphene also enables picosecond non-radiative transfer of TMD excitonic species. Starting from a given initial X h density, transfer of X h to graphene will reduce the maximum achievable density of X 0 and of other longer lived neu-tral excitonic compounds. The latter will be strongly quenched by graphene, whereas the former will be minimally affected owing to their picosecond radiative lifetime. As a result, X 0 exclusively contribute to the PL spectra of TMD/graphene heterostructures. The measured X 0 PL intensity is largely determined by the competition between X 0 formation and non-radiative X h transfer to graphene rather than by the trade-off between radiative X 0 recombination and non-radiative X 0 transfer to graphene.

Graphene is here introduced as narrow-line filter that is naturally tuned to a broad range of emitted photon energies spanning the mid-infrared to the ultraviolet regions. Our two-dimensional design naturally outperforms alternate solutions based on spectrally narrow interference filter that are considerably bulkier and lack tunability (see supplementary Section 9). Going further, highspeed (up to ∼ 1THz), photonic and opto-electronic devices with one single bright and nearly lifetime-limited emission line (see supplementary Section 2) can be envisioned using TMD/graphene heterostructures. Such devices may also benefit from the excellent electrical contact, photodetection [START_REF] Massicotte | Picosecond photoresponse in van der Waals heterostructures[END_REF][START_REF] Arp | Electronâeur"hole liquid in a van der waals heterostructure photocell at room temperature[END_REF], electron and spin transport [START_REF] Kelly Luo | Optovalleytronic spin injection in monolayer MoS2/few-layer graphene hybrid spin valves[END_REF][START_REF] Avsar | Optospintronics in graphene via proximity coupling[END_REF] capabilities offered by TMD/graphene heterostructures. One may also foresee progress in cavity quantum electrodynamics [START_REF] Schneider | Twodimensional semiconductors in the regime of strong lightmatter coupling[END_REF], chiral optics [START_REF] Chervy | Room temperature chiral coupling of valley excitons with spin-momentum locked surface plasmons[END_REF] and opto-valleytronics [START_REF] Mak | Light-valley interactions in 2d semiconductors[END_REF] by jointly exploiting the simple emission spectra of TMD/graphene heterostructures and their record-high degrees of valley coherence and valley polarization of up to 60 % and 50 %, respectively [START_REF] Lorchat | Roomtemperature valley polarization and coherence in transition metal dichalcogenide-graphene van der waals heterostructures[END_REF].

Methods

Our model system is a van der Waals heterostructure formed by stacking a monolayer of graphene onto a TMD monolayer using standard methods as in ref. [START_REF] Castellanos-Gomez | Deterministic transfer of two-dimensional materials by all-dry viscoelastic stamping[END_REF][START_REF] Zomer | Fast pick up technique for high quality heterostructures of bilayer graphene and hexagonal boron nitride[END_REF]. In this work, we have investigated MoSe 2 , MoS 2 , WSe 2 and WS 2 -based heterostructures encapsulated in hexagonal boron nitride (BN, see Fig. 1-3 and Fig. 5) or directly deposited on SiO 2 substrates (Fig. 4). All materials were mechanically exfoliated from bulk crystals. Graphene and TMD monolayers were unambiguously identified using room-temperature Raman and PL spectroscopies, respectively. Our samples were investigated at variable temperature (4 K -300 K) by means of micro-PL and differential reflectance (DR) spectroscopy using home-built setups. Time-resolved PL measurements were performed on MoSe 2 -based samples, using a Ti:Sa oscillator delivering ≈ 2 ps pulses with a repetition rate of 80 MHz and a synchro-scan streak camera with a temporal resolution of ≈ 1.5 ps. All comparisons between results obtained on TMD and on TMD/graphene are based on measurements performed in the same experimental conditions on a same TMD flake partially covered with graphene (see for example Fig. 2).

S2. APPROACHING THE HOMOGENEOUS LIMIT

As shown in Table S1, most of our BN-capped samples display Γ X 0 of a few meV and, in any event, significantly below 10 meV (see Table S1). Considering that τ X 0 ≈ 2 ps (see Fig. 4,5 and also Sec. S8), we would expect a lifetime-limited Γ min X 0 = /τ X 0 ≈ 0.3 meV. Figure S1 shows the PL spectra of another BN-capped MoSe 2 /graphene sample exhibiting a particularly narrow Γ X 0 down to 2.2 meV. Although Γ X 0 remains dominated by broadening due to disorder and dephasing, these results

show that one can approach the homogeneous limit in TMD/graphene heterostructures. Along this line, we observed that narrow PL linewidth can also be achieved in MoSe 2 /graphene heterostructures without the need for an extra BN top layer. In Fig. S2, we report PL spectra of a MoSe 2 monolayer deposited onto boron nitride (BN) and covered only by single (1LG) and bilayer (2LG) graphene. We observe nearly identical and narrow Γ X 0 , near 2 meV (FWHM) in the 1LG/MoSe 2 /BN and 2LG/MoSe 2 /BN heterostructures. The X 0 PL intensity I X 0 is only quenched by a factor 2.2 in 1LG/MoSe 2 /BN as compared to the vacuum/MoSe 2 /BN reference and, expectedly [START_REF] Chen | Energy transfer from individual semiconductor nanocrystals to graphene[END_REF] the X 0 PL quenching factor Q X 0 (see Table S1) only increases up to a factor of 3 in 2LG/MoSe 2 /BN.

As we will further discuss in Sec. S9, these results demonstrate that using a single layer of graphene is an optimal solution since X 0 emission is already very efficiently filtered with minimal PL quenching (see also Table S1 and Fig. 4 in the main text for related data on SiO 2 supported MoSe 2 /graphene). (bottom, dark red). The X 0 exciton energy, linewidth and integrated PL intensity (I X 0 , in arbitrary units) are indicated. The spectra were recorded at T = 15 K with a laser photon energy of 2.33 eV.

S3. ASSIGNING THE LOW-ENERGY EMISSION LINES IN WSE2 AND WS2

-1 2 0 -8 0 -4 0 0 4 0 -1 5 0 -1 0 0 -5 0 0 5 0 P L I n t e n s i t y ( a r b . u n i t s )

E -E X 0 ( m e V ) W S e 2 X 0 X * X D L E -E X 0 ( m e V ) X X * / X D L W S 2 X * S X * T X 0 FIG. S3.
Photoluminescence lines in WSe2 and WS2. PL spectra of BN-capped WSe2 (left) and WS2 (right) recorded at 14 K under cw laser excitation at 2.33 eV and 1.96 eV, respectively, as in Fig. 1 of the main text. The origin of the energy axis is taken at the X 0 peak energy. The PL spectrum of WS2 is shown on a semi-logarithmic scale for clarity. The low-energy PL lines below X 0 are assigned in keeping with recent reports [START_REF] Courtade | Charged excitons in monolayer WSe2: Experiment and theory[END_REF][START_REF] Vaclavkova | Singlet and triplet trions in WS2 monolayer encapsulated in hexagonal boron nitride[END_REF][START_REF] Wang | In-plane propagation of light in transition metal dichalcogenide monolayers: Optical selection rules[END_REF]. X D denotes a spin-dark exciton, X S and X T are the singlet and triplet trions, XX denotes a charged biexciton and L refers to localised states, whose physical origin is still debated. Let us note that exciton-phonon replicas may also contribute to the low energy side of the PL spectra [START_REF] Liu | Valley-selective chiral phonon replicas of dark excitons and trions in monolayer WSe2[END_REF]. Also, in the case of WS2, XX and X D are expected at very close energies [START_REF] Nagler | Zeeman splitting and inverted polarization of biexciton emission in monolayer WS2[END_REF][START_REF] Wang | In-plane propagation of light in transition metal dichalcogenide monolayers: Optical selection rules[END_REF]. MoS2/graphene (centre), and WS2/graphene (right) heterostructures, akin to the measurements in Fig. 2f of the main text.

S4
The prominent DR and PL features are assigned to X 0 . All data were recorded below 20 K in the linear regime under continuous wave (cw) laser excitation at 2.33 eV (MoS2/graphene, WS2/graphene) and 1.96 eV (WSe2/graphene). The full width at half maximum of the PL spectra Γ X 0 are indicated. Note that the data on WSe2 stem another sample than the one shown in S5b. Evidence for TMD neutralization at room temperature.

M o S e 2 ( a ) ( b ) ( c ) X * X 0 2 s B X 0 M o S e 2 / G r E n e r g y ( e V ) M o S 2 / G r x 1 0 0 M o S 2 B X 0 X * 1 . 8 1 . 9 2 . 0 2 . 1 2 . 2 B X 0 ( d )
E n e r g y ( e V )

x 5

W S 2 / G r P L I n t e n s i t y ( a r b . u n i t s )

x 1 0 0 W S 2 X 0 X * X 0
E n e r g y ( e V )

x 1 0 0 W S e 2 / G r W S e 2 X * X 0 X 0
E n e r g y ( e V )

FIG. S7. Trion-free PL spectra at room temperature. PL spectra of BN-capped TMD/graphene heterostructures compared to those of a nearby BN-capped TMD reference, all recorded in ambient air in the linear regime under cw laser excitation at 2.33 eV. The PL spectra in TMD-graphene are quasi symmetric whereas the PL spectra from TMD exhibit a lower energy shoulder that arises predominantly from trions (X ). The scaling factors allow estimating the large room temperature PL quenching factors [START_REF] Froehlicher | Charge versus energy transfer in atomically thin graphene-transition metal dichalcogenide van der waals heterostructures[END_REF] that strongly contrast with the low X 0 PL quenching factors observed at cryogenic temperatures (see main text and Table S1). The X 0 lines are slightly redshifted in TMD/graphene, as discussed in the main text, in Fig. S5, S6 and in Ref. 29 and 37. The red lines are multi-Lorentzian fits to the data, with their different components shown with grey dashed lines. Hot luminescence from excited excitonic states (e.g., X 0 2s and B excitons) is clearly visible in MoS2/graphene and MoSe2/graphene.

1.8 1.9 2.0 2.1 2.2 normalised by the incoming photon flux (Φ ph ) and the integration time. Φ ph is color-coded with a gradient ranging from dark red (low Φ ph ∼ 100 nW/µm 2 ) to yellow (high Φ ph ∼ 1 mW/µm 2 ). PL saturation due to exciton-exciton annihilation [START_REF] Mouri | Nonlinear photoluminescence in atomically thin layered WSe2 arising from diffusion-assisted exciton-exciton annihilation[END_REF] is clearly visible in WS2, whereas a quasi linear scaling is observed in WS2/graphene. The PL spectra in WS2 remain quasi symmetric even under high Φ ph , whereas the PL spectra from the TMD reference exhibit a lower energy shoulder, assigned to trion (X ) emission. The latter grows significantly as Φ ph increases and ultimately overcomes the X 0 line, as shown in (b) on the selected spectra recorded at Φ ph ≈ 2 × 10 23 cm -2 s -1 and plotted on a linear scale.

S6. EXCITON BINDING ENERGY

Encapsulation in BN and more generally screening by a surrounding medium significantly reduce the exciton binding energy E b , as discussed for instance in Ref. [START_REF] Raja | Coulomb engineering of the bandgap and excitons in two-dimensional materials[END_REF]. In this section, we discuss PL and differential reflectance (DR) measurements, which allow us to provide a fair estimation of E b in our samples, also useful to estimate the changes in exciton radiative lifetime induced by graphene (see Sec. S8.1).

S6a. BN capped MoSe2/graphene

First, on the BN-capped MoSe 2 /graphene sample discussed in Fig. 2 and3, we find splittings ∆ 1s-2s = 110 ± 2 meV between the X 0 1s and X 0 2s states and ∆ 1s-3s = 127 ± 4 meV between the X 0 1s and X 0 3s states (see fit in Fig. 3c and Fig. S9). ∆1s-2s (black squares) and ∆1s-3s (red circles) between the X 0 1s and the X 0 2s and X 0 3s excitons, respectively. The data are extracted from the PL spectra shown in Fig. 3a and shown as a function of the cw incoming photon flux at 2.33 eV and T = 4 K.

S6b. BN-supported MoSe2/graphene

We also measured ∆ 1s-2s ≈ 113 meV and ∆ 1s-3s ≈ 135 meV using PL spectroscopy (as in Fig. 3 andS9) in the 1LG/MoSe 2 /BN sample introduced in Sec. S2 (see Fig. S2). The X 0 2s and X 0 3s features nearly merge into one slightly asymmetric feature in 2LG/MoSe 2 /BN and we estimate ∆ 1s-2s ≈ 109 meV. The reference region of the sample (vacuum/MoSe 2 /BN) displays ∆ 1s-2s ≈ 153 meV and its 3s feature merges with the low energy wing of the hot PL feature from the 1s B exciton (B 1s ) that is near 210 meV above X 0 in all parts of the sample. Interestingly, although this sample is not covered by a BN thin layer, these energy shifts are very similar to the values reported in Fig. 3 and S9 in a BN-capped sample. These observations suggest that the screening experienced by a "bare" TMD monolayer deposited onto a transparent substrate experience is marginally affected by the presence of a top dielectric layer. Let us also stress that sample to sample variations in the energy splitting between excitonic states may reflect various levels of dielectric disorder, as recently investigated in details in Ref. [START_REF] Raja | Dielectric disorder in two-dimensional materials[END_REF] nescence (similar to the data in Fig. 3) from the 2s (X 0 2s ) and 3s (X 0 3s ) A excitons as well as from the 1s B excitons in the BN-supported sample introduced in Sec. S2 and Fig. S2. Note that the X 0 2s and X 0 3s features merge in 2LG/MoSe2/BN. The energy scale is shown relative to the 1s exciton (X 0 ) energy E X 0 . The spectra were recorded at T = 15 K with a laser photon energy of 2.33 eV. The Raman 2D-mode features of single layer and bilayer graphene appear near 2.00 eV, i.e., around 370 meV above the X 0 lines.

S6c. BN-capped MoS2/graphene

Similarly, using differential reflectance and PL spectroscopy, we could measure ∆ 1s-2s ≈ 136 meV and ∆ 1s-2s ≈ 171 meV in BN-capped MoS 2 /graphene and BN-capped MoS 2 sample, respectively, as shown in Fig. S11.

S6d. Discussion

The measured ∆ 1s-2s and ∆ 1s-3s in TMD/graphene heterostructures must be compared with the larger splittings observed TMD samples (see Fig. S9 221 meV were found, respectively, while the 1s-2s splittings were 168 meV and 170 meV, respectively.

Assuming for simplicity that the exciton binding energy reduction is proportional to the reduction of the ∆ 1s-2s , we can estimate binding energies E b ≈ 150 meV in our BN-supported and BN capped MoSe 2 /graphene samples and 176 meV in our BN-capped MoS 2 /graphene sample, respectively. Our results reveal that one single layer of graphene significantly reduces E b by up to ∼ 30 % irrespective of the presence of a BN top layer. Our findings on E b are summarised in Table S2.

S7. ESTIMATING LASER-INDUCED HEATING AND EXCITON DENSITIES

In order to estimate the laser induced heating in our measurements, we have monitored the X 0 energy and linewidth (E X 0 and Γ X 0 ) as a function of the incoming photon flux Φ ph . As shown in Fig. S12 (data extracted from the spectra in Fig. 3a), we only observe minimal X 0 downshifts of at most 2 meV, associated with spectral broadening up to 1.5 meV.

Considering the temperature dependence of E X 0 and Γ X 0 , we can conservatively estimate that the temperature laser induced temperature rise at our sample is well below 30 K up to incoming photon flux Φ ph ∼ 10 23 cm 2 s -1 and remains below 70 K at up to the highest values of Φ ph employed in our study. Regarding the steady state excitonic density, we assume that we are in the linear recombination regime since the X 0 PL intensity is linearly increasing with Φ ph . Assuming an X 0 lifetime of 2 ps (see Fig. 4 and Fig. 5) and an absorption coefficient near 10 % at 2.33 eV [START_REF] Li | Measurement of the optical dielectric function of monolayer transition-metal dichalcogenides: MoS2, MoSe2, WS2, and WSe2[END_REF], we can estimate maximal injected densities of hot excitons n h ∼ 2 × 10 5 -6 × 10 10 cm -2 ) for the range of Φ ph employed in Fig. 3. Note also that time-resolved PL measurements were performed using picosecond oscillators with pulse fluence below a few 10 12 photons/cm 2 . In these experiments, the laser photon energy was tuned between the 1s (X 0 1s ) and 2s (X 0 2s ) excitonic states. Assuming a conservative upper bound of 5 % for the MoSe 2 monolayer absorptance in these conditions, we can estimate that n h does not exceed ∼ 10 11 cm -2 , values for which we have verified that our samples were still in the linear regime.

Above this threshold, Q X 0 does not significantly increase further as ∆ augments up to 600 meV. These results suggest that the rise of Q X 0 near ∆ ≈ 175 meV cannot solely be assigned to a resonance with the X 0 2s state in MoS 2 but suggests that X h generated above the free carrier continuum associated with the A excitonic manifold (for instance, hot B excitons) have a higher transfer efficiency to graphene than hot X 0 1s excitons. S1).

Since the X 0 lines have slightly distinct energies in MoS2 and MoS2/graphene, Q X 0 is evaluated after interpolation of the PLE data in the top panel. The energy shifts between X 0 1s and the X 0 2s and B1s as well as E b are indicated in the bottom panel for MoS2/graphene. All data were recorded at a temperature of T = 15 K.

S9. PL OF A TMD MONOLAYER ONTO A METAL THIN FILM.

Using a 2D metallic layer such as graphene instead of a thin film of bulk metal is certainly advantageous in view of applications. Our work establishes that a single atomic layer of graphene warrants highly efficient filtering based on selective energy transfer. Nevertheless, thin films of bulk metals, such as Au, Ti, Pt. . . are routinely used as electrical contacts to 2D materials in electronic and optoelectronic devices and deserve special attention. Metallic thin films will be unavoidably rougher than 2D materials all the more so if the 2D materials are deposited on Boron Nitride (BN). As a result, van der Waals coupling between a metal film and an atomically thin semiconductor will be weaker than within a van der Waals heterostructure and the metal/TMD interface will be much more inhomogeneous than a van der Waals heterointerface. Such inhomogeneities are prone to affect the emission characteristics of the TMD monolayer.

As shown in Fig. S14, we have performed PL experiments on a MoSe 2 Monolayer deposited onto a 60 nm-thick Au film and compared the PL spectrum of MoSe 2 on Au to that of a neighbouring region of the MoSe 2 flake lying onto SiO 2 .

At room temperature, we observe large PL quenching (akin to previous findings [START_REF] Froehlicher | Charge versus energy transfer in atomically thin graphene-transition metal dichalcogenide van der waals heterostructures[END_REF][START_REF] He | Electron transfer and coupling in graphene-tungsten disulfide van der Waals heterostructures[END_REF]) and significant broadening of the PL spectra suggesting nanoscale variations of the coupling between MoSe 2 and Au. At low temperature, we observe a complex, even broader PL spectrum, where the X 0 and X lines can tentatively be identified. In stark contrast with the case of TMD/graphene heterostructures, we still observe strong X 0 PL quenching, sizeable X emission, as well as evidence for disorder, inhomogeneous broadening and exciton localization, as shown in Fig. S14d.

In other words, while the PL spectrum of MoSe 2 /graphene only reveals intrinsic X 0 emission, even when the MoSe 2 layer lies on SiO 2 (see Fig. 4 and Table S1), MoSe 2 on Au displays prominent extrinsic PL features. It is therefore clear that using layered metals, ideally in the 2D limit is undoubtedly preferable than using bulk metals in view of the photonic and optoelectronic applications based on the concepts introduced in our manuscript.

FIG. 1 .

 1 FIG. 1. Graphene as a versatile emission filter. Bright, single, and narrow-line photoluminescence (PL) spectra in TMD/graphene heterostructures are shown in the lower panel. The PL spectra of neighboring BN-capped TMD regions are shown for comparison in the upper panel. A sketch of the van der Waals heterostructure is shown in each panel. All spectra are normalized to unity relative to their most intense feature. The scaling factors indicated for each material allow direct comparison between the PL intensities in BN-capped TMD and BN-capped TMD/graphene. The bright neutral exciton (X 0 ) lines in bare TMD are indicated by asterisks. All measurements were performed at temperatures below 20 K, in the linear regime with continuous wave laser excitation at 2.33 eV (MoSe2, MoS2, WS2) or 1.96 eV (WSe2).

FIG. 2 .

 2 FIG. 2. Neutralizing an atomically thin semiconductor with graphene. (a) Optical image of a BN-capped MoSe2/graphene sample deposited onto a SiO2 coverslip. Maps of the neutral exciton (X 0 ) emission FWHM (Γ X 0 ) (b) and integrated intensity I X 0 (c). (d) Map of the trion (X ) integrated PL intensity (I X 0 ). No X emission is observed over the whole MoSe2/graphene area. Differential reflectance spectra ∆R/R and PL spectra of (e) MoSe2 and (f) MoSe2/graphene, taken at the spots indicated in white and red on (b-d), respectively. The inset in (f) shows the PL spectrum of MoSe2/graphene on a semi-logarithmic scale. The data are recorded at a temperature of 4 K, in the linear regime using continuous wave laser excitation at 2.33 eV.

2 FIG. 3 .

 23 FIG.3. Laser power dependent photoluminescence in BN-capped TMD/graphene at 4 K. (a) Semi-logarithmic cascade plot of the PL spectra of the BN-capped MoSe2/graphene sample shown in Fig.1,2, recorded under cw excitation at 2.33 eV with increasing photon fluxes Φ ph . The spectra are normalized by Φ ph and by the integration time and are vertically shifted for clarity. (b) Dependence of the integrated intensity of the neutral 1s exciton (X 0 brown), sum of the first and second excited neutral excitons X 0 2s and X 0 3s (orange) and photoinduced trion (X , green). The solid lines are fits based on a power law and the critical exponents β are indicated. (c) PL spectrum recorded at Φ ph = 3 × 10 23 cm -2 s -1 showing the X 0 and X features on a linear scale. The X 0 2s and X 0 3s features are shown in the lower inset, where the red line is a double-Lorentzian fit to the data, with the X 0 2s and X 0 3s features individually shown with dashed grey lines. The upper inset in (c) shows the energy difference between X 0 and X as a function of Φ ph .

FIG. 4 .

 4 FIG.4. Low-temperature exciton dynamics. (a) PL spectra of bare MoSe2 monolayer (blue) and of a MoSe2/graphene heterostructure (red, thicker line), both deposited onto a SiO2 substrate (see sample sketches in (b)-(d). The right inset shows the data on a semi-logarithmic scale. The grey-shaded area highlights a low-energy PL tail from localised (L) states in bare-MoSe2 that is massively quenched in MoSe2/graphene. A three-level system is shown on the left inset. The blue wavy arrow indicates the exciting laser pump pulse that generates a population of hot excitons (X h ). The latter relax with a lifetime τ rel to form cold excitons (X 0 ), from which radiative recombination occurs with a lifetime τ rad X 0 . The presence of graphene induces non-radiative decay of X h and X 0 with timescales τ h G and τ 0 G , respectively. A similar sketch may be drawn for X and other excitonic sates. Time-resolved PL of the neutral exciton feature (X 0 ) in MoSe2/graphene (b), and in bare MoSe2 (c). The longer-lived tail in the bare MoSe2 PL decay is attributed to exciton localisation. (d) TRPL of the trion feature (X ) in MoSe2. All data were recorded at 14 K in the linear regime under excitation with ps laser pulses at 1.76 eV. The thin solid lines are mono-exponential fits to the data after convolution with the instrument response function (IRF, grey area). The extracted X 0 and X lifetimes (τ X 0 and τX , respectively) are indicated.

FIG. 5 .

 5 FIG. 5. Evidence for hot exciton transfer to graphene. (a) PL spectra of BN-capped MoSe2 monolayer (blue) and a BN-capped MoSe2/graphene heterostructure (red), both deposited onto a SiO2 coverslip (see sample sketches in (b)-(d)). The PL spectrum of BN-capped MoSe2 is scaled down by a factor 7.3 for a clearer comparison. Time-resolved PL of the neutral exciton feature (X 0 ) in BN-capped MoSe2/graphene (b), and in BN-capped MoSe2 (c). The longer lived tail in the MoSe2 PL decay is attributed to exciton localisation. (d) TRPL of the trion feature (X ) in MoSe2. All data were recorded at 7 K in the linear regime under excitation with ps laser pulses at 1.73 eV. The thin solid lines are fits to the data using the three-level model shown in the inset of Fig. 4a, after convolution with the instrument response function (IRF, grey area). The extracted hot exciton relaxation times (τ rel in (b), τ rel in (c)) as well as the X 0 and X decay times (τ X 0 and τX , respectively) are indicated.

  FIG. S2. Bright, single and narrow line emission in BN/MoSe2/graphene. PL spectra of a MoSe2 monolayer directly deposited on BN (top, blue line), partly covered by a single layer of graphene (middle, orange) and by a bilayer of graphene

Fig. 1

 1 Fig. 1 in the main text. The broad DR feature observed near 1.68 eV in this sample is an artifact arising from the underlying substrate.

  FIG. S8. Neutrality and photostability under high photon flux at room temperature. (a) Laser power dependent photoluminescence spectra of a BN-capped WS2/graphene heterostructure compared to a nearby BN-capped WS2 reference, recorded in ambient air using cw laser excitation at 2.33 eV. The spectra are shown on a semi-logarithmic scale and are

F

  FIG. S9. Dielectric screening and reduced exciton binding energy in BN-capped MoSe2/graphene. Splittings

  FIG. S11. Dielectric screening and reduced exciton binding energy in BN-capped MoS2/graphene. From top to bottom: differential reflectance (DR), its derivative and photoluminescence (PL) spectra (shown in semilog scale) of a BNcapped MoS2 sample (left, blue traces) and a neighboring BN-capped MoS2/graphene region (right, dark red traces). The relevant excitonic states are indicated by vertical dashed lines. The horizontal dashed lines in the middle panels indicate the zero of the DR derivative. All measurements were done at T = 15 K. The PL measurements were done with an incoming laser photon energy of 2.33 eV.

  FIG. S12.Estimating laser-induced heating. Comparison between the X 0 PL peak energy and linewidth (FWHM, Γ 0 X ) recorded as a function of the temperature set in our cryostat (a), and b), respectively) and as a function of the incident photon flux Φ ph for the BN-capped MoSe2/graphene sample studied in Fig.2-3of the main manuscript. The slight excitonic redishift and broadening observed here allow us to estimate that laser-induced sample heating is minimal and remains below 70 K at under the highest Φ ph employed here. The red line in (a) is a fit based on Varshni law.

D=E

  FIG. S13.Photoluminescence excitation spectroscopy (PLE) of the sample introduced in Fig.S11. Integrated intensity of the X 0 PL line as a function of ∆, the energy shift between the incoming photon energy and X 0 PL line (near 1.93 eV) in BN-capped MoS2 (top panel), and BN-capped MoS2/graphene (middle panel). Open symbols correspond to a second measurement run on the same sample. The bottom panel shows the X 0 PL quenching factor Q X 0 (see also TableS1).

2 FIG. S14 .

 2S14 FIG. S14. Photoluminescence spectroscopy of MoSe2 on a gold substrate. (a) Optical and (b) room temperature photoluminescence (PL) images of a bare MoSe2 monolayer deposited at the border between a SiO2/Si substrate and a gold (Au) thin film. (c) and (d) PL spectra of MoSe2 on SiO2 (red) and on Au (blue) recorded at room temperature (c) and at 15 K (d). "L" indicates a sizeable contribution from localised states giving rise to a low-energy shoulder in the reference spectrum on SiO2 that gives a prominent feature in the PL spectrum of MoSe2 on gold.

  . IDENTIFYING THE X 0 LINE IN TMD/GRAPHENE HETEROSTRUCTURES

	(a.u.)	WSe 2 /Gr			MoS 2 /Gr		WS 2 /Gr
	DR/R
	(a.u.)
	Intensity	G X 0=7.7 meV		G X 0=4.0 meV		G X 0=4.2 meV
	PL
		1.65	1.70	1.75	1.85	1.90	1.95	2.00 2.04 2.08 2.12
		Energy (eV)			Energy (eV)	Energy (eV)

FIG. S4.

Identifying the X 0 line. Differential reflectance (DR) and PL spectra of BN-capped WSe2/graphene (left),

.

  Echantillon « 2018 » sans BN top Luis, peux tu vérifier que la calib est la même que sur la diapo 3 ?

				B 1s		E X 0= 1.639 eV
			X 0 2s
	units)		X 0 3s	vacuum/MoSe 2 /BN
	(arb. Intensity	X 0 2s	X 0 3s	B 1s	2D SLG/MoSe 2 /BN	E X 0= 1.633 eV
	PL	X 0 2s +X 0 3s			2D
				B 1s
						BLG/MoSe 2 /BN	E X 0= 1.628 eV
		100		200	300
			E-E X 0 (meV)
	FIG. S10. Dielectric screening and reduced exciton binding energy in BN/ MoSe2/graphene. Hot photolumi-

Acknowledgements

The authors thank D. Basko, T. Galvani, L. Wirtz, G. Schull, S. Azzini, T. Chervy, C. Genet, M.A. Semina and M.M. Glazov for fruitful discussions. We are grateful to H. Majjad and M. Rastei for help with AFM measurements, to M. Romeo, F. Chevrier, M. Acosta, A. Boulard and the StNano clean room staff for technical support. We acknowledge financial support from the Agence Nationale de la Recherche (under grants H2DH ANR-15-CE24-0016, 2D-POEM ANR-18-ERC1-0009, D-vdW-Spin, VallEx, and MagicValley), from the LabEx NIE (Under Grant ANR-11-LABX-0058-NIE) and from the EUR NanoX (under grant VWspin and MILO).

Competing interests

The authors declare no competing interests.

Supplementary Information for: Dynamically-enhanced strain in atomically-thin resonators

Note on the labelling of excitonic states

In the main text, X 0 refers to bright, neutral 1s A exciton with center of mass momentum within the light cone. In the discussion associated with Fig. 4 and Fig. 5, these excitons are referred to as cold excitons, as opposed to hot excitons (X h ), i.e., 1s excitons with center of mass momentum outside the light cone. In the following sections, we shall consider excited states from the A excitonic manifold, labelled X 0 2s , X 0 3s , as well as the 1s B exciton B 1s . When necessary, we will use the full X 0 1s notation to refer to cold excitons.

S1. PL PEAK ENERGIES, LINEWIDTHS AND QUENCHING FACTORS S1. Emission characteristics for the samples shown in Fig. 1 of the main text. Peak emission energy (E X 0 ), full width at half maximum of the X 0 emission line (FWHM, denoted Γ X 0 ) for the PL spectra of the four BN-capped samples discussed in Fig. 1 in the main text, as well as for the sample deposited on SiO2 discussed in Fig. 4 of the main text (data highlighted with symbols). We also consider two PL quenching factors: first, Q X 0 the ratio between the integrated intensities of the X 0 line in TMD (I X 0 ) and in TMD/graphene (I X 0 ); second, Qtot the ratio between the total PL integrated intensity in TMD (Itot) and I X 0 (that corresponds to the total PL intensity in TMD/graphene). The data were extracted from Lorentzian fits for BN-capped samples and graphene/MoSe2/SiO2 and from a Voigt fit for vacuum/MoSe2/SiO2. Noteworthy, we observe that Γ X 0 is generally smaller on TMD/graphene heterostructures than on TMD, suggesting that graphene further reduces disorder induced broadening and pure dephasing (see also Sec. S2). This effect is particularly striking in our SiO2 supported sample, since the bare MoSe2 reference does not benefit from BN encapsulation. Q X 0 remains below 10 in all samples under study and is even smaller than 1 in our SiO2 supported sample.

S5. SUPPLEMENTARY DISCUSSION ON THE ABSENCE OF PL FROM TRIONS

S5a. Neutralizing a TMD monolayer with graphene

Different scenarii may explain the absence of X absorption and emission features in TMD/graphene. Let us first assume that the TMD coupled to graphene remains doped. Trions may then form rapidly but their slow radiative recombination (in the 20-200 ps range [START_REF] Robert | Exciton radiative lifetime in transition metal dichalcogenide monolayers[END_REF][START_REF] Fang | Control of the exciton radiative lifetime in van der waals heterostructures[END_REF]) is quenched by graphene. We may thus still be able to observe an X absorption feature in the DR spectra, in contrast with the measurements in Fig. 2e. Furthermore, since the X PL feature is more than three orders of magnitude weaker than the X 0 PL feature (see inset in Fig. 2f), the X lifetime would be reduced to less than ∼ 100 fs, an unrealistically low value. Alternatively, graphene may fully quench hot excitons before they can relax and form X 0 and X near resident carriers. However, X and X 0 formation are equally fast in MoSe 2 (see Ref. [START_REF] Robert | Exciton radiative lifetime in transition metal dichalcogenide monolayers[END_REF][START_REF] Fang | Control of the exciton radiative lifetime in van der waals heterostructures[END_REF] and Fig. 4,5). As a result, this scenario would imply massive X 0 PL quenching, in obvious contradiction with our observations. The third and most plausible course of events is that all the native dopants in the TMD (either electrons or holes, with a typical density on the order of 10 11 -10 12 cm -2 ) transfer to graphene, leading to a slight increase of the Fermi level of graphene (typically by less than 100 meV) and to the observation of intrinsic absorption and emission. This scenario is corroborated by room temperature Raman scattering [START_REF] Froehlicher | Charge versus energy transfer in atomically thin graphene-transition metal dichalcogenide van der waals heterostructures[END_REF] and PL measurements (see Fig. S7,S8).

S8. SUPPLEMENTARY DISCUSSION ON EXCITON DYNAMICS

In this section, we provide additional insights into the physical origin of the PL quenching discussed in the main text and give an estimate of the non-radiative exciton transfer time to graphene and of the X 0 PL quantum yield.

As already introduced, the relaxation of X 0 in TMD is essentially radiative with a short lifetime τ rad X 0 of typically a few ps [START_REF] Palummo | Exciton radiative lifetimes in twodimensional transition metal dichalcogenides[END_REF][START_REF] Robert | Exciton radiative lifetime in transition metal dichalcogenide monolayers[END_REF][START_REF] Fang | Control of the exciton radiative lifetime in van der waals heterostructures[END_REF]. In PL measurements, TMD samples cannot be resonantly excited at the X 0 energy and the X 0 state is populated after phonon-assisted relaxation of hot excitons (denoted X h ), on a timescale τ rel (see inset in Fig. 4a). Now, τ rel and hence the X 0 formation and relaxation dynamics depend strongly on the environment. Due to a larger disorder, τ rel ∼ 1 ps or less in SiO 2 supported samples [START_REF] Robert | Exciton radiative lifetime in transition metal dichalcogenide monolayers[END_REF], whereas X h relaxation can be as long as τ rel = 18 ps in state of the art BN-capped samples [START_REF] Fang | Control of the exciton radiative lifetime in van der waals heterostructures[END_REF]. This value is significantly longer than τ rad X 0 , irrespective of modifications of τ rad X 0 due to dielectric screening and to the Purcell effect [START_REF] Fang | Control of the exciton radiative lifetime in van der waals heterostructures[END_REF]. In addition, exciton dynamics and in particular X h relaxation a priori depend on the incoming photon energy.

S8a. Radiative liftetime and exciton transfer time

For the sake of simplicity, in Fig. 4 of the main text, we have presented a low-temperature time-resolved PL (TRPL) study of a SiO 2 supported MoSe 2 monolayer partially covered by a graphene monolayer. In such a samples, the formation of X 0 is faster than their radiative decay and cannot be experimentally resolved. Therefore, the TRPL measurements in Fig. 4 can safely be fit to the convolution of our IRF and an exponential decay. We have found nearly equal excited state lifetimes τ X 0 ≈ 2.3 ps in graphene/MoSe 2 /SiO 2 and in vacuum/MoSe 2 /SiO 2 (see Fig. 4b,c), suggesting that the non-radiative transfer time of X 0 excitons to graphene τ 0 G is significantly longer than τ rad X 0 in graphene/MoSe 2 /SiO 2 . Let us note, however, that due to dielectric screening, τ rad X 0 is expected to be slightly longer in graphene/MoSe 2 /SiO 2 than in vacuum/MoSe 2 /SiO 2 . As a result, observing similar τ X 0 in graphene/MoSe 2 /SiO 2 and in vacuum/MoSe 2 /SiO 2 may be coincidental and result from a compensation between the increase of τ rad X 0 and a contribution from non-radiative energy transfer of X 0 with a timescale τ 0 G 2.3 ps.

As discussed in Sec. S6, screening of the Coulomb interactions induced by semi-metallic graphene reduces the exciton binding energy or equivalently increases the exciton Bohr radius. Thus, the radiative lifetime, which scales as

b , will increase due to the presence of graphene [START_REF] Robert | Exciton radiative lifetime in transition metal dichalcogenide monolayers[END_REF]. Taking the values shown in Table S2, we can estimate that τ rad X 0 in BN-capped MoSe 2 /graphene is approximately 2 times longer than in the bare MoSe 2 reference. A similar value is obtained for the BN/MoSe 2 /graphene sample discussed in Fig. S2 and Fig. S10 that is not covered by a top BN layer and hence has a layout similar to the SiO 2 supported sample discussed in Fig. 4. Considering the X 0 radiative lifetimes τ rad X 0 ≈ 2.3 -2.4 ps in MoSe 2 monolayers (see Fig. 4 and Fig. 5), we estimate that τ rad X 0 and the X 0 exciton transfer time to graphene τ 0 G are both close to 5 ps at cryogenic temperatures (here 15 K). Note that as described in the main text and in Sec. S8.3, the transfer of X h to graphene is likely to be more efficient than the transfer of zero momentum, optically active X 0 1s . Let us point out that the presence of a single layer of graphene with larger refractive index than BN may further increase τ rad X 0 . However, as discussed in Ref. [START_REF] Fang | Control of the exciton radiative lifetime in van der waals heterostructures[END_REF][START_REF] Froehlicher | Charge versus energy transfer in atomically thin graphene-transition metal dichalcogenide van der waals heterostructures[END_REF], the inclusion of an atomically thin layer in a multi-layered system has a negligible effect on the local field enhancement experienced by the TMD monolayer and we can safely consider that changes in τ rad X 0 in TMD/graphene heterostructures essentially stem from screening of the Coulomb interactions induced by graphene.

S8b. Emission quantum yield of the X 0 state We first define the total emission quantum yield η tot as the number of emitted photons divided by the number of absorbed photons. The latter is defined as: η tot = η X 0 η F , with η X 0 , the number of emitted photons divided by the number of cold X 0 (i.e, X 0 1s excitons with center of mass momentum within the light cone) and η F the formation yield of cold X 0 (number of cold X 0 / number of absorbed photons). In practice, due to the limited collection efficiency in cryogenic optical setups and uncertainty in the sample absorptance, it is extremely challenging to measure η tot accurately at low temperatures. We can, however, estimate η X 0 . Indeed, it was established in Ref. [START_REF] Robert | Exciton radiative lifetime in transition metal dichalcogenide monolayers[END_REF] and 7 that at cryogenic temperatures (typically below 90 K), X 0 recombination in MoSe 2 monolayers is essentially radiative such that the measured X 0 lifetime τ X 0 can be attributed to the radiative lifetime τ rad X 0 . In other words η X 0 is very near 100% at low temperatures in MoSe 2 monolayers. Now, using the results in Fig. 4 and Fig. 5 and the discussion in Sec. S8.1, one obtains η

and BN-capped MoSe 2 /graphene heterostructures. Besides, the yield η tot also depends strongly on whether the TMD under study is a bright or dark material. In the case of bright (e.g., MoSe 2 ) TMDs, η F is limited by exciton transfer to graphene (in the case of graphene/TMD heterostructures) and by the presence of residual dopants (in the case of bare TMD), traps and neutral defects (in both TMD and TMD/graphene). In the case of dark (here W-based) TMDs, the X 0 population is also limited by the presence of lower lying dark states (X D ) that can be efficiently populated from the X 0 state. In WS 2 /graphene and WSe 2 /graphene heterostructures, formation of X D is also limited by X h transfer to graphene. As a result, η X 0 and η tot will be intrinsically smaller in W-based TMDs than in MoSe 2 , whether or not these TMDs are coupled to graphene.

S8c. Photoluminescence excitation spectroscopy

In Fig. 4 and Fig. 5, care has been taken to investigate exciton dynamics using excitation only 100-110 meV above the X 0 line in MoSe 2 , i.e., below or close to the X 0 2s line. This configuration is the same as in Ref. 6 and 7. Noteworthy, it was reported in Ref. 7 that exciton dynamics in BN-capped MoSe 2 and in particular the hot exciton relaxation time (i.e., the X 0 formation time) is independent on the energy difference ∆ between the X 0 line and the incoming photon energy for ∆ = 7 -110 meV.

To get more insights into X h dynamics and PL quenching, we have performed photoluminescence excitation spectroscopy (PLE) and extracted the X 0 PL quenching factor Q X 0 (see Table S1) as a function of ∆. We have chosen to focus our study on BN-capped MoS 2 /graphene sample shown in Fig. S11. In contrast to bare MoSe 2 , which shows sizeable emission from X (see Fig. 4 and Fig. 5), our bare MoS 2 references display minimal X emission (see Fig. 1 and Fig. S11), which allows us to compare X 0 dynamics in MoS 2 and MoS 2 /graphene without considering a significant contribution from X . Our main results are shown in Fig. S13. PLE spectroscopy permits to identify the X 0 2s and B 1s excitons, that have unambiguously been assigned by means of DR and PL measurements (see Fig. S11). The quenching factor Q X 0 reaches low values ∼ 2 for ∆ ≈ 100 meV, i.e., significantly below X 0 2s and remains roughly constant down to ∆ ≈ 33 meV. Except for strictly resonant excitation of excited excitonic states (e.g., X 0 2s ), no optically active excitons can be formed through vertical transitions. Instead, hot 1s excitons with finite center of mass momentum are formed through acoustic and optical phonon assisted processes and relax to form cold X 0 within the light cone. We attribute the residual PL quenching to non-radiative transfer of hot and cold excitons to graphene.

Remarkably, Q X 0 rises sharply up to approximately 5 to 7 above ∆ ≈ 175 meV, a value that precisely coincides with the X 0 2s state in bare MoS 2 but also with the exciton binding energy in MoS 2 /Graphene (as shown in Table S2).


Simon Dixon

Polina Proutskova

Tillman Weyde

Daniel Wolff

Martin Pfleiderer

Klaus Frieler

Frank Höger

Helene-Camille Crayencour

Jordan B L Smith

Geoffroy Peeters

Dig that Lick: Exploring Patterns in Jazz Solos

niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Author DB is now at Audible Magic, UK, and GP is now at Telecom ParisTech, France.

II. PROJECT OUTCOMES

The transcriptions are created automatically from commercial audio recordings using state-of-the-art melody extraction algorithms based on neural networks and advanced signal processing methods [START_REF] Başaran | Main Melody Estimation with Source-Filter NMF and CRNN[END_REF]. New evaluation metrics were developed to assess the suitability of extraction algorithms for tasks such as pattern matching [START_REF] Frieler | Don't Hide in the Frames: Note-and Pattern-based Evaluation of Automated Melody Extraction Algorithms[END_REF]. An overview of the technologies employed in DTL [START_REF] Weyde | Dig That Lick: A Technical Primer for Big Data Jazz Studies[END_REF], plus a detailed account of the pattern analysis [START_REF] Frieler | Towards a History of Melodic Patterns in Jazz Performance[END_REF] and three case studies [START_REF] Frieler | Anatomy of a lick. Structure and variants, history and transmission[END_REF][START_REF] Gabbard | What We Are Digging Out of the Data[END_REF][START_REF] Solis | Chasing the Trane: Quantifying the Social Journey of a Coltrane Solo[END_REF] were presented. A study on jazz improvisation was also published [START_REF] Frieler | Constructing Jazz Lines: Taxonomy, Vocabulary, Grammar[END_REF]. Web-based search applications were developed, allowing the user to search for exact and inexact patterns in multiple melody databases, to specify constraints on the metadata and patterns, and to visualise and hear the retrieved results [START_REF] Frieler | Two Web Applications for Exploring Melodic Patterns in Jazz Solos[END_REF][START_REF] Höger | Dig That Lick: Exploring Melodic Patterns in Jazz Improvisation[END_REF]. These interfaces are publicly available at the following web site: https://dig-that-lick.hfm-weimar.de/

.

  We give an overview of outcomes from the recently completed project "Dig that lick: Analysing large-scale data for melodic patterns in jazz performances", involving a multi-disciplinary and international team of researchers. On the technical side, the project built infrastructure and tools for extraction, discovery, search and visualisation of melodic patterns and associated metadata. These outcomes facilitate analysis on the musicological side of the use of melodic patterns in improvisation, to answer questions about the origins, evolution and transmission of such patterns. This in turn gives insight into the extent to which improvisers rely on patterns, the development of individual and shared styles, and the level of influence of individual musicians, based on the amount of reuse of their improvised material by later musicians.I. BACKGROUNDThe recorded legacy of jazz spans a century and provides a vast corpus of data documenting its development. Recent advances in digital signal processing and data analysis technologies enable automatic recognition of musical structures and their linkage through metadata to historical and social context. Automatic data extraction and aggregation give unprecedented access to large collections, fostering new interdisciplinary research opportunities. The Dig That Lick (DTL) project developed novel technological and musicanalytical methods to gain fresh insight into jazz history.The importance of musical patterns to jazz is well established in the scholarly literature and popular discourse. Ethnographers analyse how musicians learn and use licks; music psychologists debate the role of licks in improvisation; and fan-generated YouTube videos illustrate the remarkable popularity of one seven-note pattern known simply as The Lick. Yet many open questions remain about the development and transmission of licks in individual careers and jazz history. We investigate the usage of patterns and licks in monophonic jazz solos using search algorithms on a large database of jazz solo transcriptions.  * This research was funded under the Trans-Atlantic Program Digging into Data Challenge with the support of the UK Economic and Social Research Council (ES/R004005/1), the French National Research Agency (ANR-16-DATA-0005), the German Research Foundation (PF 669/9-1), and the US National Endowment for the Humanities (NEH-HJ-253587-17).

Centre for Digital Music, Queen Mary University of London, UK, s.e.dixon@qmul.ac.uk

City, University of London, UK

University of Music Weimar, Germany

National Center for Scientific Research, France

IRCAM, France

University of Illinois, USA

Columbia University, USA