Collart Dutilleul

Keywords: Land system, the household, responsibility system, land rights, China

nm mi in ng g U Un ni iv ve er rs si it ty y o of f S Sc ci ie en nc ce e a an nd d T Te ec ch hn no ol lo og gy y

The current land system in China is somewhat of particularity. All lands are owned by the state and collective ownership while there is no private ownership of land. Ownership of land originally means that the farmer owns the land he cultivates. However, China's current land system has led to numerous violations of human rights. This paper attempts to investigate violation of human rights, including rights for food, under the system of public ownership of land as well as how to promote human rights.

Land System in China since 1952

The "Land Reform" movement was completed under the leadership of Chinese Communist Party in 1952 and a land system of collective ownership was implemented, which put to an end the system of mainly state-owned land and partially private ownership for over two thousand years. In the vigorous process of the "Land Reform", farmers without land were exulted while all the lands owned by landlords, Kulaks, the Kuomintang government officials and warlords were confiscated and a considerable number of those land owners were killed. ① Farmers obtained fields and a socialist lofty ideal of "land to the tiller" was achieved. From a perspective of human rights, "Land Reform" is the "tyranny" for the majority, which eliminated the minority by violence and make the majority possibly live a happy life. The equality and fairness were achieved through coercion and violence. It was just because of this kind of dictatorship of the proletariat that the ruling Communist Party has supported by the majority who got hold of land.

However,the collective ownership land system was not successful according to the development in the rural areas from 1953 to 1978. Initially, only mutual assistance groups were made in the rural areas, with 4-5 rural households in each group and then were developed into primary cooperatives and senior cooperatives by 1955. In 1958's "Great Leap Forward", the People's Commune system was imposed by the Government, with an average size of about 5,000 households, 10,000 labours and 10,000 acres of land. The Commune's income was distributed mainly based on the needs of survival and only partially based on the work done by individual farmers. The agricultural products produced in the private plots were banned to trade in rural fair. Implementing People's Commune is a lofty ideal of communism in the Marxist ideology. However, the members of the Communes quickly lost their enthusiasm for work, resulting in an agricultural crisis of three-year severe famine from 1959 to 1961 when about more than 30 million people were died of non-normal. At that time, no wording of rights for food was expressed. After 1962, the People's Commune system was changed by central leaders to the rural land system of production teams as the basic ownership unit of the land, which had been implemented until 1978. The current land system in China, named the household responsibility system (HRS), began in 1978. In November 1978, the farmers from Xiaogang Village, Fengli Commune, Fengyang County, Anhui Province were unwilling to tolerate the "iron rice bowl" mode of production and started to carry out an all-round responsibility system, fix farm output ① It is estimated that death toll of land reform risen from previous 2 million to the current quantity which is between 5 million and 19 million. The involved toll increased from 25 million to 60 million. quotas for each household and work contracted to households, which was namely "the household responsibility system (HRS)", under the leadship of the production team leader Yan Junchang. In 1982, the land system of HRS was officially recognized by the Central Document No. 1 and then the People's Commune system terminated officially in China. Article 10 in the "Constitution" in 1982 stipulates that: "Land in the cities is owned by the state. Land in the rural and suburban areas is owned by collectives except for those portions which belong to the state in accordance with the law; house sites and privately farmed plots of cropland and hilly land are also owned by collectives." Thus, the land property right system of the HRS is recognized in law and political system.

Land Problems under the Household Responsibility System

The land system of the HRS greatly mobilized the enthusiasm of farmers and food production had been greatly increased. By the mid of 1980s, farmers had basically solved the problem of food and clothing in the grain-production countryside focused on growing rice and wheat. Solving the problem of food and clothing of farmers in fact meant the basic life right and the right to subsistence. Only a few years later, the problems of food and clothing of most farmers in the rural China had been resolved. Therefore, the Chinese Government has always claimed proudly to the world that the greatest achievement in human rights in China is the elimination of poverty. Indeed, solving the problem of food and clothing of nearly 800 million farmers is a monumental achievement of Chinese Government.

But the golden age of the rural areas lasted less than a decade. With Chinese government's more emphasis on the economic development in industry, especially with China joined the World Trade Organization (WTO) in December 2001, the gap between the cities and the countryside has been widened. Industrialization and urbanization requires a lot of land, farmlands close to the cities and towns in coastal areas began to be eroded. As a result, countryside is still the object of being plundered by cities.

After the "Agriculture Feeding Industry", approach of the former Soviet Union, the Chinese government has focused on the development of industry since the founding of the PRC, that is, the government practices monopoly for the purchasing and marketing of agricultural products by means of lowering the buying prices of agricultural products, increasing the selling prices of fertilizers and other industrial products to accumulate funds for the industrial development. The policy of Agricultural Feeding Industry was carried out under the planned economic system, referring to that farmers must "give enough amounts to the state and remain enough amounts to the collectives" faithfully and may keep the rest for themselves after their agricultural products harvesting." In fact, there was not much left for farmers themselves when they were forced to give enough amount to the state and collectives. At the same time, the strict household registration system locks in farmers to the land, the dual system in urban and rural areas which is divided people into two parts: registered permanent rural residence and registered permanent urban residence, under which farmers suffer from various unequal treatments and are discriminated against everywhere.

From the late 1980s to the mid 1990s, unequal treatment suffered by farmers had been increased. Farmers had the right to manage their land through the household contract responsibility system and seemed to control their own destiny. Theoretically, farmers could decide what they grew and how they priced and sold their agricultural products, but they had to pay various agricultural taxes that were the basic sources for the daily expenditures spent by the township governments and various rural public service expenses. Though farmers had their rights to control their land, they are still not capable of dealing with the township government's exploitation. Consequently, Three Rural Issues unique in China had been formed. A lot of farmers resisted against the scot negatively or actively and some were imprisoned, tortured and even died. In 2001, the Three Rural Issues was extremely serious. All the agricultural taxes were cancelled by the Central Government, which finally freed farmers from the heavy taxes. As a result, rural China returned to the situation in form before the year of 1949.Without daily expenditures, township governments did not support farmers. Though farmers got rid of governmental officials, they lost the financial support. Without the governmental financial support, the whole rural China was in an anarchical and abandoned condition. It is generally believed that before 1949 China's countrysides were of rural gentry society or acquaintance society in which countrysides' daily affairs and public service such as water conservancy, bridge building, weddings and funerals were handled by the elders with a certain prestige. Due to the very lower mobility at that time, the countrysides presided over by rural gentries were maintained through the established morality, rules and customs. However, when population movements become easier, more importantly, when the young farmers work in cities with a monthly income of more than a yearly farming income at home, the rural gentries can not control farmers who want to make a fortune any more. Meantime, villager elections that farmers directly elect their own village committees carried out in rural China almost completely deviated from the original intention of villager elections. The elected village heads are persons who served their own interests through trickery and swindling or abused power for personal gains, rather than respected rural gentries. Or even local gangleader were elected as village heads by vote-buying.

Land System in China during the Process of Rapid Economic Growth and Urbanization

In the recent 20 years, Chinese economy and society are characterized by rapid economic growth and urbanization that both have a huge demand for land. With a market economy adopted in China since 1992, the Chinese economy has maintained an annual growth rate of over 10%. By 2010, China's GDP ranks the second in the world, a large number of cheap migrant workers sought jobs in cities that supported the rapid economic growth. China's rapid economic growth largely is due to the rapid expansion of city and the central government's policy of developing small cities. Economic development and urbanization have occupied a lot of land and than many issues of human rights are caused by land issues, while incomplete the HRS can not stop these human rights violations from occurring. The impact of industrialization and urbanization, the HRS full of loopholes, these loopholes are as follows:

First, the main part of land property is not clear. Although China's Constitution and Land Management Law define that rural land are collectively owned, but the collective is refer to the village government, township government, county or provincial government or the central government, the law has not been clearly defined. In fact, land ownership is generally controlled by the village cadres and the hands of county-level government officials. Since property rights are unclear, therefore, the right of land contract is not stable; there are some problems with the land use rights of farmers, so it is seldom to expand production with additional fixed investment in land. Also, because the using right is not imperfect, farmers are lack of mortgage land use rights to obtain the right to bank loans. It is also the subject of land ownership is not clear and easy to the government officials who seek an opportunity for personal gain.

Second, that property rights are not clear leads to serious deficiencies in the land requisition system. The Central Government to implement industrialization and urban development strategy, the state can rely on their ultimate ownership of agricultural land, by way of expropriation, free land expropriation and violation of the collective ownership of farmers and farmers the right to land contractual management. The government also can rely on their administrative power to intervene the farmers right to use the land. Especially in the 1994 tax system reform and the main indicators to GDP performance evaluation mechanism, the local government through the land to big projects, big industry, and real estate finance to support the urban construction land.

Considerable number of local government collusion with real estate developers, the formation of interest groups to jointly raise the urban housing prices, the majority of farmers in land acquisition process have lost their land, ① farmers without land, mainly through complaints to the provincial capital, and Beijing, to express themselves. Unfortunate, the data show that the petitioners in the present, there are more than half due to land disputes. At the same time, the land acquisition process of corruption has become a hotbed of corruption, Chinese officials, hundreds of billions of money into the personal pockets. ② Due to land acquisition and the great injustice caused a large number of groups induced events and social contradictions, seriously affecting the stability of Chinese society.

Third, the lack of clear land transfer mechanism. China's very limited arable land, Chinese farmers cultivated area per capita is 1.88 mu, and the United States is 1480 mu, which is 787 times that of farmers in China, 18 million acres is considered to be the final bottom line, any arbitrary act of agricultural land will be occupied Severely punished.

① According to statistics, half of real estate prices came from refunding land transfer by the government, half of the local finance income came from real estate, the price of real estate in Shanghai, Beijing and Hangzhou, Shenzhen and Guangzhou leap into the front ranks in the world, the capital city of other houses also needed a middle-income decades of income to buy the house. ② Wang huaizhong,, former vice-governor of Anhui Province, abusing his power for his daughter by 3500 mu with low price, making profits 2800 million by changing hands, being bribed for selling land in illegal ways, there are examples such as Zhang zhiguan, who was the, taking bribery money of 8.6 million Yu zhijun, who was, ,taking bribery money of 5.39million, and as well as Chang who was the orginial minister from natural resource, dismissed and prosecuted because of land. 80% corrupt officials are related to land.

However, over the years, a lot of land has been idle, was prepared by the real estate business hoarding excessive profits. Although the government allows rural residents to transfer the right to manage a 30-year land to other individuals or companies by way of a contract, subcontract, lease, exchange, transfer, stock cooperative. But in the coastal economically developed areas, neither are large areas of land circulation nor development, but leave land uncultivated, because in these developed areas, farmers can work rations earned money to buy. To grow food in their mind is a thankless job and do not earn money.

Harmfulness of Land System and Land Acquisition to the Human Damage

From about 60 years of China's land system, human rights were violated under any land system. In other words, the land system is not directly associated with the protection of human rights. Protection of human rights in China is achieved mainly through government's administrative means, for the law's role in the protection of human rights is very limited. Even though there already are some land use management laws and regulations, such as Constitution, Property Law, Land Management Law, Rural Land Contract Law, Rural Land Contract Disputes Mediation and Arbitration Law, the government often breaks the law but requires people to abide by the law inversely. Therefore, the public is difficult to use the law to protect their rights. The damages on the rights of farmers caused by the current land system are as following:

First, under the urban-rural dual system the output and input of land resources is still disproportionate, as the government does make the inactive conduct, the rights to survival and food of farmers are not guaranteed. Statistical data show that since the reform and opening up through the land and resources taken away from farmers at least 3 trillion or more, far more than 30 years of reform and opening up by the scissors away from the peasants of the 6 billion dollar. As the Government has not yet been bigger in the land system changes or adjustments, therefore, to account for the restricted mode of production units to improve productivity, agriculture uncompetitive, low value-added agricultural products, and other basic means of production such as seeds, fertilizer prices under the control of manufacturers, together for the farmers on the land only with great access to basic food rations to pay to meet basic survival needs. And when faced with natural disasters time to eat well is a problem of individual farmers. Some scholars believe that the negative action of governments brings about the development of rural areas is difficult; in fact, undermine the right to development of farmers. ① Second, the property rights of landless peasants have been violated, their right to life, which also could be express rights for food, can not be guaranteed. Landless farmers is currently a specific title in China, which refers that in the process of city development, the famers live here have to give their field due to the needed land for the construction of the industrial base, factories and urban residential zones and public facilities, and these no land migrant workers have become Three-No-Farmers who have no land, no post and no basic cost of living allowances. According to expert estimates, now there are about 50 million landless peasants. These diverted land generally increase in value twofoldness ranging from several times to dozens of times, if the owners of agricultural land have bargaining ① Liu Zhaojun, Peasants Right Protection in the idea of Human Right, China Land Science, July, 2010, p20. power, then the land property owners will enjoy the benefits of the land, but in fact most farmers do not have bargaining power. Current land management law only provides for the total of land compensation fees and resettlement fees shall not exceed the toplimit of thirtyfold average annual output value before three years of land requisition, but there is no lower limit must be met, therefore, local governments in the actual implementation often arrive lower demand not higher so that the compensation many farmers actually receive falls far short of 30 times.

Third, the current land expropriation compensation is the basis of agricultural income. But due to the different purpose of land, land profit is vary huge. As is engaged in the industrial development land benefits, which is can reach hundreds times of agricultural land. According to Jiusan Society calculation, the levied land income distribution pattern roughly is local government 20% to 30%, enterprise 40% to 50%, village organization 25% to 30%, farmers only 5% to 10%.The huge price is from difference between the granting land cost and the land grant fee, which mostly were grabbed by middlemen and local government. ① Only the remaining 5% of the land grant fee was get by partly farmers who put money in the bank to provide for the aged. But currency devaluation, is not almostly predict whether the money can be used to pension. The money is used to work at risk investment by partially farmers. Also the money is squandered by some farmers in a few years. The farmers who are no land will lose basic production and living material, their endowment becomes a big problem. The rule of Item of Clause 25 in the Universal Declaration of Human Rightsis, "everyone has the right to enjoy living standards, which is maintain themselves and their families for the health and welfare" become empty talk. ② Fourth, the farmers' rights to know, the right to freedom of expression and rights of relief are violated. Seen from the large number of cases, most of the land agreements are completed in the black-box operation, the villagers know a little of their transactions between the government and businessmen, even in full unknowable of the completion of land transactions; also have some land is local forces land through illegal means transactions. Land acquisition process as a great injustice, and the higher level government officials, village leaders and local forces in the native land of great benefit gained in the process, the farmers here can not be reconciled punish the corrupt officials insist, when the local villagers have complaint not satisfied, they go to the provincial capital, or Beijing to petition that will become the only way to solve the problem. In China, maintaining social stability is the government's top priority, th the Central Government compel that leapfrog petition must be zero, the expression of those who dare to exercise their right to petition leapfrog the "trouble-making" is not in custody, sent to a mental hospital, is subjected to torture, beatings sometimes. Today's China is not particularly landless peasants remedies, the survival of landless peasants in Chinese society will be a major social problem.

Fifth, the migration rights of farmers will be hurt. In the process of demolition and ① An outline of reformation of the land property system reference by China's Reformation Forum, http://www.chinareform.org.cn/Economy/Agriculture/Forward/201010/t20101014_46761.htm,2011-5-6 ② Article 25 of Universal Declaration of the Human Rights states that Everyone has the right to a standard of living adequate for the health and well-being of himself and of his family, including food, clothing, housing and medical care and necessary social services, and the right to security in the event of unemployment, sickness, disability, widowhood, old age or other lack of livelihood in circumstances beyond his control. Motherhood and childhood are entitled to special care and assistance. All children, whether born in or out of wedlock, shall enjoy the same social protection.

land expropriation, a considerable number of "city-village", the so-called "city -village" is that when urban expansion, the original rural changed into the villages which is in city, they scattered in the town, because their cheap rent fee, they often become the preferred residence of the migrant workers in Rio DE janeiro, Brazil, are called slum in Mumbai, India. City-Villages from the start of urban construction became the "nails", the leadership often will lie in municipal construction as his achievements, therefore, tear down villages for governments and real estate valued.

After demolition, how to compensate and whether to move back on time, the government and the villagers are in game. If the two sides fail to reach an agreement, the Urban Guard or the employment of the underworld thugs chased the villagers to fight the "nail house", who refused to move out. ① Those nail house often been held against the demolition of violence, and some died by way of self-burning to protest the government's demolition of acts of violence. ② China's Constitution provides citizens with the right to freedom of movement and malignant in a case of forced migration has been repeatedly trampled.

Sixth, the farmer rights to education, social welfare rights are injured. China's reform starts from the countryside, but the countryside is left behind by far very long than the city after more than ten years late, the city of Guangdong Zhejiang river delta as a huge gluttonous most young sucked by the vampire in several provinces such as around Guangdong, Guangxi, Hunan and Jiangxi, and western Yun-Gui-Chuan of rural areas. Formerly once thought that these people are exiling home do not leave the earth, but certain years later, many people did not hope, because in that native land and the city compared is really the too backward: education quality low rural primary school, the potable water not health, the facility crude medical service in small clinic, evening and slack farming season time, the villagers besides playing mahjong, did not have any entertainment facility nearly, kept in the village only then old person and the child, the countryside is faded from the memory gradually. Exits not to hope, old being unable to get away, after small grows up, must exit. The ruined countryside and the city on the wane the exquisite comfortable environment formed "the power which so-called the farmer entered a city namely to come from agricultural the thrust force, also came from urban the pulling force." ③

What Land System Can Better Protect Human Rights

Human history and current public and private land system is nothing less than two, the implementation of the low number of public ownership of land, mainly socialist countries and some developing countries, private ownership of land is found in most of the world countries, such as Civil Law in France, Italy, Germany and Switzerland, and the Common Law of the United States, Canada, India, UK, private land accounts for the vast majority of all land assets, a small state-owned land. In these countries, mainly by the market allocation of private land, sometimes by the government to regulate, another state-owned, public and private land is always the dynamic changes. China's land should be public or private, there are three opinions in China, one that should be maintained and improve the existing the HRS, and second, advocates of land owned by the state and the third is land privatization initiatives.

Clearly, the implementation of which the land system is bound up with a country's social system, political and economic systems, legal systems, traditions and customs, history, heritage and way of thinking about. Typically, a country's land system is relatively fixed, incremental innovation, and whether to change their country's land system depend up the situation of a country and the international community. In the contemporary community, human rights as an important factor has impacted a national land system. Particularly, in the basic human rights concepts and standards, personal interests, the interests of the weak are placed in front of the nation, when the tillers of the soil are no fields, or their land was occupied, even if the tillers are fewer, the land system is flawed. Because "the right to property is sacred and inviolable, except when the legitimate needs of clearly identified public when necessary, and compensation in a fair condition in advance, no person shall be deprived of property." ① Today, "We live in an age rights era, the era of human rights is widely accepted that the only political and moral values." ② Regardless of what the implementation of the land system, a fair priority, followed by efficiency and land conservation. Or balancing fairness and efficiency, when the two can not take into account, the expense of fairness can not be efficient, on the contrary, to be fair to sacrifice efficiency. Under the Universal Declaration of Human Rights and Civil and Political Rights International Conventions and Economic, Social and Cultural International Conventions, survival, which means rights to food and land, is the most important rights. How to food and land as the entitlement, property rights are basic. Later the land property extended out on the basis of civil rights and other social rights. Unfortunately, in reality, there is fairness and efficiency are often contradictory, on the one hand, the lack of equitable land system is often inefficient, on the other hand, high efficiency, the back of the land system is often a lack of fairness. From this point, only to land rights and food to rights as human rights, the end of the land as farmers and the survival of the most fundamental habitat, ③ to the fairness as the land policy formulation and implementation of the basic principles, such a policy is "good" the land policy, the only way to truly achieve the highest moral ideal of contemporary society -fairness and justice.

① Déclaration des Droits de l'Homme et du Citoyen, clause 17. ② Louis Henkin: "Toward an Age of Right", Beijing, Intellectual Property Press, 1997, p89. ③ Her Xuefeng, the expert on rural problem, stated that peasants returning to countryside and the well-off life are the basic rights. However, a lot of farmers were still the second class citizens because of the urban and rural disparities. See He Xuefeng : Going Back to the Land is the Basic Human Right, Journal of Huazhong University of Science and Technology, (Social Science Edition), January of 2009, p.16.

  Local scholars such Mr. Li Changpin, Dr. Yu Jianrong and Professor Xu Yong have a deep explored to the Three Rural Issues and more in details see the book Will the Boat Sink the Water? written by two local writers in 2004. ①

①

  Such examples could be multiple indefinitely. Eight villages in the Haerbin City of Heilongjiang Province thought the illegal compensation of demolition. All of them are arrested. See Haerbin's policy office issue the case of illegal resist demolition by violence in March 28, China Daily May of 5 th , 2011.

②

For instance, Ms. Tang Fu-zhen, a entrepreneur of 47 years of age, prevent a demolition team with force on November 13, 2009, she self-immolated on the roof. The local government regarded as "oppose violence with violence." The example of "insult by insult " is nothing new now. See Tang Fu-zhen: Prevent Demolition by Self-Burning, http://news.ifeng.com/mainland/special/2010fazhilanpishu/renwupian/detail_2010_12/27/3713359_0.shtml,2011-5-6 ③ He Xuefeng : Going Back to the Land is the Basic Human Right, Journal of Huazhong University of Science and Technology, (Social Science Edition), January of 2009, p.15.

 The Lascaux program (2009-2014) is linked to the 7th Framework Programme of the European Research Council ("IDEAS"). "Lascaux" is headed by François The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement n° 230400. of my speak on the 4th Nantes World Forum on Human Rights in 28-30, June, 2010.


Giovanni Carini

Giuseppe Carini

Giovanna D ' Angelo

Gaspare Tripodo

Laura Orsingher

Aldo Fontana

Low temperature specific heats of permanently densified glassy GeO 2

Keywords: glass, thermal properties, vibrational properties PACS number: 63.50.+x, 65.40.+g, 78.30.Ly

Measurements of specific heat have been performed over the temperature interval between 0.4 K and 25 K in glasses of GeO 2 , which have been compacted at pressures of 2 GPa and 6 GPa achieving more than 20% of densification. Above 1 K, the specific heat C is reduced by up to a factor of 2.5 with increasing density, this variation being stronger than that observed below 1 K. The broad peak observed above 1 K in a C/T 3 vs. T plot shifts to higher temperatures with increasing density, exhibiting changes which cannot be explained by the modifications of the elastic continuum. In addition to this, the peak shows no changes in shape as a clear indication that the overall distribution of the underlying vibrational modes is independent of density. The temperature dependence of C over the whole explored range is in qualitative agreement with the predictions of the Soft Potential Model.

I. Introduction

Glasses exhibit physical behaviours whose understanding represents a fundamental and complex argument of the condensed matter physics. The nearly linear specific heat C [START_REF]Amorphous Solids: Low Temperature Properties[END_REF][START_REF] Pohl | [END_REF] observed below a few Kelvin and the subsequent broad hump in C/T 3 [3], the Boson peak (BP) which refers to an excess vibrational modes over the classical Debye density of states [3,4] and the plateau of the thermal conductivity κ(T ) at around 10 K [5] exhibit a remarkable universality which appears to be quite insensitive to the chemical composition of glasses. It is believed that all these experimental findings have excess low-energy excitations (LEE), which exist beside phonons, as a common origin: LEE, whose investigation is a long-standing problem of considerable interest, take their origin from the disordered topology of amorphous structures. Concerning the low-temperature anomalies observed below 1K, the successful tunnelling model [6,7] associates the defect modes to single atoms or groups of atoms subjected to quantum-mechanical tunnelling between two different stable positions available in the glassy network and schematizes the locally mobile "particles" by asymmetric double-well potentials.

Less clear is the physical origin of the THz frequency dynamics in glasses causing the BP, the hump in C/T 3 and the anomalous characteristics of the phonon transport above few Kelvin. The BP and the broad hump in C/T 3 are considered as a manifestation of the enhanced low-energy vibrational dynamics having as a common origin an excess density of vibrational states (DVS), whose nature is a topic, at present very debated [8,9].

A possibility to investigate this matter is to modify the glassy matrix in a controlled way and to observe the correlated changes in different physical properties. This can be obtained by producing structural changes of the glassy network with compaction of the material by high pressures (GPa range).

Irreversible compaction of a glass produces significant structural modifications giving rise to a substantial modification of the intermediate range order by cold densification [10]. Permanent densification makes it possible to study indirectly the effects of pressure on physical properties, such as the thermodynamic measurements, for which it is usually difficult to carry out in situ high pressure experiments. Remarkable changes are in fact observed in the linear specific heat [11], the hump in C/T 3 and the frequency of the Boson Peak [12][13][14][15], and also in the internal friction [16] and the sound velocity [17]. Measurements on permanently densified samples can provide information on the microscopic mechanisms governing the LEE, mainly when the observations are compared with the microscopic structural changes. Permanent densification assumes an important role in the investigation of LEE, also because it permits to get controlled variations of the topology of the glassy network without changing the stoichiometry. Increasing density of GeO 2 glasses obtained by cold densification leads to a growing packing of tetrahedral structural units building up the network: the system acquires a structure having a more efficient packing to fill in the lesser volume available to it [18]. These structural changes cause a significant reduction of the local atomic mobility and, consequently, of the anomalies characterizing the [13,17]. This could represent an important further step toward a phenomenological understanding of an open question: the possible correlation between the low-energy excitations determining the properties governed by tunnelling systems and those regulating the intermediate-temperature vibrational behaviours, that is the hump in C/T 3 and the BP. With the aim of investigating the relation between quantum tunnelling and additional vibrations governing the THz region, we present here a study concerning the low temperature specific heat in GeO 2 glasses, permanently densified by increasing pressures. Differently from the observations in compacted v-SiO 2 where coherent changes of the specific heat were revealed over the whole temperature interval explored [11], the present results show that, above 1 K, the specific heat C is significantly reduced with increasing density exhibiting variations stronger than those observed below 1 K. As explained in the following, these differences are believed to be a consequence of a wider range of investigated densifications (more than 20 %) which cause more substantial modifications of the intermediate range order.

II. Experimental Details

Vitreous germania GeO 2 was prepared by the conventional melt-quenching method. Some cuts of the same sample were successfully densified by a multi-anvil HT&HP (high temperature and high pressure) apparatus. They were compressed at 2 and 6 GPa and heated under pressure at 673 K for 2 minutes; the pressure was released after a quick cooling down. The final products were homogeneous and permanently densified ingots having both diameter and length of about 5 mm. The densities were measured at room temperature by a Micrometrics Accupyc 1300 gas pycnometer under helium gas with an accuracy of 0.03%, obtaining the values of 3.99 g/cm 3 (2 GPa) and 4.52 g/cm 3 (6 GPa), which correspond to 9% and 23% of densification with respect to the density of normal glass (3.66 g/cm 3 ).

After the synthesis and also one year later, the densified GeO 2 glasses were characterized by X-ray diffraction which did not reveal any sign of local or extended crystallization. In the following, we will refer to the samples using the pressure at which they were densified.

Longitudinal and shear sound waves were obtained by tuning X-and Y-cut quartz crystals at their fundamental frequency. The sample-transducer bonding agent was N-Apiezon grease. The sound velocity measurements of longitudinal (v l ) and shear (v t ) waves were performed at 10 MHz and at room temperature by a pulse-echo technique using an apparatus described elsewhere [19]. The velocity of longitudinal ultrasounds was also measured in all the glasses down to 1.5 K by using a standard liquid helium cryostat in the range between 1.5 and 20 K and a cryo-generator above 10 K. Correction which takes into account the bonding was not carried out, but a rough evaluation of the corresponding error introduced in the velocity gave a value less than 0.05%. The low temperature values of shear sound velocities have been evaluated by assuming as temperature independent the value of the ratio v l /v t obtained at room temperature. The specific heat of GeO 2 glasses was measured using an automated calorimeter, which operated by the thermal relaxation method, in a 3 He cryostat over the range between 0.4 and 2 K and in a 4 He cryostat between 1.5 and 25 K. Samples of about 20-30 mg were bonded to a silicon chip as sample holder by vacuum grease Apiezon N to optimise the thermal contact. A SMD resistor, as temperature sensor, and a constantan strain gauge, as heater element, were attached to the other chip surface using a thermosetting resin. The good agreement between the measurements taken by the two different experimental setups operating below and above 2 K is apparent from the figures. The random error and any systematic errors are believed to be less than 3-4%.

III. Results and discussion

The experimental data of the specific heat C(T) obtained between 0.4 K and 23 K for normal and densified (at 6 GPa) GeO 2 glasses are compared in Figure 1. The data of normal glass above 3 K are in very good agreement with earlier experimental observations on vitreous GeO 2 [20], reported as a solid line in the same figure. In the overall temperature interval explored, both the samples exhibit an excess C(T) over the Debye contribution C D (T), whose behaviour for the 6 GPa glass is reported as a dotted line in Figure 1. When plotted as C(T)/T 3 vs T (Figure 2), the specific heat for all the studied samples evidences the characteristic shape for a glass determined by an upturn below 2 K and a broad peak above 2 K. Growing densification depresses C(T) over the whole temperature interval explored giving rise to a significant decrease of the hump and to an increase of the peak temperature T peak , which shifts from about 8.5 K in normal GeO 2 , through 11.3 K in 2 GPa glass, to about 12.6 K in 6 GPa glass. The Debye contributions (dashed-dotted lines in Figure 2) have been evaluated using the classical relation where the term in square bracket is the inverse of the cubic power of the average Debye sound velocity v D and the other parameters have their usual meaning. The values of v D and some other useful parameters are included in Table 1. In order to compare the changes of the excess specific heat to the modifications of the elastic continuum, we report in a plot C(T) scaled by the Debye contributions C D of normal and densified GeO 2 glasses vs T/Θ D (Figure 3a). The elastic Debye temperatures are: Θ D =305 K for normal glass, Θ D =336 K for 2 GPa glass and Θ D =381 K for 6 GPa glass. It results that the ratio C(T)/C D decreases with increasing densification, also exhibiting a well defined shift of the maxima which implies a variation of T peak stronger than that experienced by Θ D . This finding evidences that GeO 2 glass, densified up to more than 20%, shows changes of low-energy vibrational dynamics which are not accounted for by the transformations of the elastic continuum. A further remarkable result is

3 3 3 3 3 4 B 2 v 2 v 1 3 1 5 k 2 T c T C D t l D =               + = ρ π h F o r P e e r R e v i e w O n l y
given by the comparison of the humps reported in Figure 2 scaled by

peak T C       3
, see Figure 3b: despite the significant variations observed in the amplitude and the position of the hump with increasing density, all the scaled curves overlap showing an identical shape. The invariance of the shape leads to conclude that all the vibrational modes, extended and quasi-localized, contributing to the hump form a distribution which is independent of density. Both the observations discussed above are in agreement with the results of studies concerning the low temperature specific heat in compacted SiO 2 [11] and in situ high pressure inelastic neutron scattering measurements on poly-isobutylene (PIB) [21,22]. Even if, as pointed out in SiO 2 [23], measurements with in situ applied pressure cannot be simply compared to the observations in permanently densified samples retrieved from the same interval of pressure, these results concerning the low energy vibrational dynamics appear to be quite general and independent of the specific experimental conditions.

Among several theoretical models, proposed so far to account for the excess density of vibrational states, one of the most attractive is the Soft Potential Model or SPM [24,25] because it provides an unified description of all the anomalies observed at low (below 1 K) and high temperatures. Furthermore, a not negligible detail, it permits a quantitative comparison with the experimental behaviours. In the SPM, the low-frequency vibrational dynamics in a glass is described in terms of localized excitations which coexist with ordinary phonons. These excitations are realized in anharmonic or soft atomic potentials, represented by a fourth degree polynomial:

              +       ξ +       η = 4 3 2 0 a x a x a x E ) x ( V ( 1
)
where x is an appropriate configurational coordinate having the dimension of a length, E 0 is of the order of the atomic binding energy, η and ξ are small dimensionless parameters with a random distribution of their values. The expression of V(x) includes both double-and single-well potentials. The lowest-energy excitations (double wells) correspond to the well known two level systems (TLS) with a nearly constant density of states. At higher energies there are the quasi-local harmonic oscillators (HO) which occur in single-well potentials and have a density of states following a ω 4 -dependence. Both the excitations interact with phonons in the same way, the interactions being either resonant or relaxational. At temperatures (T<<W/k B ) small compared with the energy W, which sets the crossover between TLS and HO excitations, a linear T-dependence for the specific heat is determined by the contribution of TLS's: where P 0 determines the TLS density of states and the other symbols are defined in Ref. [25]. At higher temperatures, a large contribution to the specific heat is provided by HO's whose rapidly increasing density of states leads to a T 5 dependence [25]:

              = ) T ( t T k W ln T k W P 9 2 (T) C min exp B 3 / 1 2 B 5/2 L 0 3 / 1 2 TLS τ η π (2)
C (T k P k T W HO B L 5/2 B ) =       8 63 2 6 0 5 π η (3)
The fourth-power HO density of states changes to a density of delocalized vibrational excitations for an energy scale even higher than a characteristic energy E d . This is because the average distance between the HO's with E≥E d becomes smaller than the wavelength of a phonon with about the same energy.

Consequently an excitation can directly jump from an oscillator to another producing "delocalization" of HO excitations. The DVS must be reconstructed and a linear dependence on the energy results [25],

which corresponds to a T 2 -dependence for the vibrational specific heat in the high temperature region.

Crossover from the low temperature linear dependence to a T 2 -behaviour, through a T 5 -dependence, leads to a minimum at a temperature T min and to a maximum at T max ≅E d /5k B in the temperature dependence of C(T)/T 3 . From T min , the value of the characteristic energy W can determined: W∼2 k B T min .

Following the predictions of SPM, we analyze the specific heat data over the temperature region below T max by the relation

5 5 3 3 1 ) C(T T c T c T c + + = ( 4
)
where the first term in the r. h. s. of Eq. ( 4) refers to TLS contribution, the second one to the overlap of the elastic Debye contribution and the eventual excess usually observed in glasses [START_REF] Pohl | Low temperature specific heat of glasses[END_REF], and finally the third term evaluates the HO contribution. The fits, reported in Figure 2 as dotted lines, reproduce quite well the experimental curves up to 5-7 K giving values of the parameters which are included together with those of 1. The values of c 1 , c 3 and c D derived for normal glass are in good agreement with those previously obtained by Stephens [START_REF] Stephens | [END_REF]. We like to remark, however, that a more exhaustive analysis of the TLS contribution should require a study extended to lower temperatures than those available in the present experiment and, as a consequence of the restricted temperature range, our considerations are to be considered as highly tentative. Inspection of the behaviour of the parameters of the fits and of the maximum of the peak,

4 1 5 1 min T         = c c in Table
peak T C       3
, in densified glasses shows that growing densification appears to be more efficient in depressing the LEE contributing to the hump than TLS responsible for nearly linear specific heat below 1 K. In fact, glass, while c 1 by a factor of 1.25. This result is quite different from the observations in compacted vitreous SiO 2 [11], where C is reduced by about the same factor over the whole temperature range explored (0.1 K<T<35 K), and suggests a possible different microscopic origin for the low energy excitations giving rise to TLS and to the hump (or the BP) in GeO 2 glass. Previous neutron and x-ray diffraction studies [18,28] of densified GeO 2 glasses gave strong evidence for a reduction in the length scale of the intermediate-range order induced by cold densification up to 10 GPa, excluding a transition from a GeO 4 tetrahedral to a GeO 6 octahedral structure. The densification process has been described in terms of a step-like behavior: in the first step there is a decrease in the sizes of the network cages, associated with a closer packing of the relatively rigid tetrahedra [28]. Further increase of pressure leads to a reconfiguration of the system via a rotation of the tetrahedra around the Ge-O-Ge bonds, which causes a distortion of the GeO 4 tetrahedra and a more efficient packing of oxygen ions to fit to the growingly reduced volume [18]. These structural changes should hinder the local mobility of GeO 4 tetrahedra, causing a significant reduction of low energy excitations (soft vibrations and tunneling states) and also a shift to higher frequencies of the local vibrational modes involved.

An interesting consideration concerns the density variations of the energy crossover W, which is related to the other SPM's parameters by [25]:

M M W         ≅ M V ρ h ( 5
)
where M is the average mass of the atoms constituting the glass (for GeO 2 , M =34.87 a.u.), M the effective mass of the moving group, ρ the density and V the sound velocity. In order to evaluate the ratio M M , we use the values of ρ, V and T min (determining the energy W) reported in Table 1. The SPM does not distinguish between longitudinal and shear sound velocity and, tentatively, we use the average Debye sound velocity. The obtained values of M M decreases from 6.5 in normal glass to 4.5 in 6 GPa sample pointing to an apparent reduction of the effective mass of the moving group.

It is concluded that densification at elevated pressures of GeO 2 glasses causes network modifications associated to the formation of more packed and tied groups of atoms and depresses the local mobility of the units which are the source of additional low-energy excitations over the contribution of the ordinary elastic waves. The reduced mobility of these "quasi-particles" leads to growingly smaller contributions to the vibrational specific heat and to the scattering of thermal phonons which are responsible for the heat transport in a glass. Strong support for the latter consideration is given by the low temperature behaviour of the thermal conductivity κ in a densified SiO 2 glass: a substantial increase of the magnitude of the plateau characterizing κ in normal vitreous silica is observed, corresponding to an increase of the phonon mean free path [29]. By exploring an interval of densifications (up to 23 %) quite larger than the one investigated in v-SiO 2 (up to about 11 % [11]), it has been possible to disclose the following peculiarities:

(i) the modifications of medium range structure give rise to a more severe reduction of additional soft vibrations involved in the excess specific heat than that experienced by TLS;

(ii) the hardening of the elastic continuum with increasing densification is not sufficient to account for the changes observed in the excess C;

(iii) the invariance of the shape of C/T 3 with increasing densification indicates that the vibrational modes causing the low temperature specific heat cannot be separated in extended and quasilocalized modes, because they are hybridized and form an overall distribution independent of densification.

IV. Conclusions.

A study of low temperature specific heat C in permanently densified GeO 2 glasses has revealed an excess C over that predicted by the Debye theory which decreases with increasing densification.

Between 2 K and 25 K, C/T 3 shows a hump which shifts towards higher temperatures and decreases by up to a factor of 2.5 in the glass compacted at 6 GPa. Below 2 K, an additional contribution is also observed: C follows an approximately linear temperature dependence disclosing a well-definite reduction by up to a factor of 1.25 with increasing densification. These observations lead to conclude that glass densification reduces the excess density of low-energy vibrational states over the Debye prediction, affecting also, but to a less extent, the density of two-level systems which are the source for the linear term. Moreover the results prove unambiguously that the density variations of the low-energy vibrational dynamics cannot be accounted for by the modifications of the elastic continuum.

  by up to a factor of 2.5 in the 6 GPa

Figure 1 .

 1 Figure 1. The temperature dependence of the specific heat C in normal ( ) and densified at 6 GPa ( ∇ ) GeO 2 glasses. Earlier experimental observations on normal vitreous GeO 2 [20] are reported as a solid line for comparison. Dashed-dotted line indicates the elastic Debye contribution C D of densified glass calculated from sound velocity data. Dotted line marks the super-linear contribution observed below 0.8 K.

Figure 2 .

 2 Figure 2. The temperature dependence of C(T)/T 3 for densified GeO 2 glasses: normal glass, ( ); 2 GPaglass, (▲); 6 GPa-glass, ( ∇ ). The dashed-dotted lines show the elastic Debye contributions calculated from sound velocity data. Dotted lines are the fits to Eq. (4).

Figure 3 .

 3 Figure 3. (a) Comparison of the specific heats of densified GeO 2 glasses, plotted as C/C D vs T/Θ D :normal glass, ( ); 2 GPa-glass, (▲); 6 GPa-glass, ( ∇ ).

  Fig.1

Table 1 .

 1 Parameters of normal and densified GeO 2 glasses. The values of the density ρ  are taken at room temperature. The values of longitudinal (V l ) and shear (V t ) sound velocities at 1.5 K are included together with the calculated Debye sound velocity V D .

	Analysis of experimental behaviours reveals that they are in qualitative agreement with the predictions
	of the Soft Potential Model.
	.

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