We present a study of electrical and thermal transport in Weyl semimetal WTe_(2)down to 0.3 K.The Wiedemann-Franz law holds below 2 K and a downward deviation starts above.The deviation is more pronounced in cleaner s...We present a study of electrical and thermal transport in Weyl semimetal WTe_(2)down to 0.3 K.The Wiedemann-Franz law holds below 2 K and a downward deviation starts above.The deviation is more pronounced in cleaner samples,as expected in the hydrodynamic picture of electronic transport,where a fraction of electron-electron collisions conserve momentum.Phonons are the dominant heat carriers and their mean-free-path does not display a Knudsen minimum.This is presumably a consequence of weak anharmonicity,as indicated by the temperature dependence of the specific heat.Frequent momentum exchange between phonons and electrons leads to quantum oscillations of the phononic thermal conductivity.Bloch-Grüneisen picture of electron-phonon scattering breaks down at low temperature when Umklapp ph-ph collisions cease to be a sink for electronic flow of momentum.Comparison with semi-metallic Sb shows that normal ph-ph collisions are amplified by anharmonicity.In both semimetals,at cryogenic temperature,e-ph collisions degrade the phononic flow of energy but not the electronic flow of momentum.展开更多
The in-plane electrical and thermal conductivities of several polycrystalline platinum and gold nanofilms with different thicknesses are measured in a temperature range between the boiling point of liquid nitrogen （...The in-plane electrical and thermal conductivities of several polycrystalline platinum and gold nanofilms with different thicknesses are measured in a temperature range between the boiling point of liquid nitrogen （77K） and room temperature by using the direct current heating method. The result shows that both the electrical and thermal conductivities of the nanofilms reduce greatly compared with their corresponding bulk values. However, the electrical conductivity drop is considerably greater than the thermal conductivity drop, which indicates that the influence of the internal grain boundary on heat transport is different from that of charge transport, hence leading to the violation of the Wiedemann-Franz law. We build an electron relaxation model based on Matthiessen＇s rule to analyse the thermal conductivity and employ the Mayadas ＆ Shatzkes theory to analyse the electrical conductivity. Moreover, a modified Wiedemann-Franz law is provided in this paper, the obtained results from which are in good agreement with the experimental data.展开更多
CrP has many exotic physical properties due to a four-fold degenerate band crossing at the Y point of the Brillouin zone,which is protected by the nonsymmorphic symmetry of the space group.We carried out the heat capa...CrP has many exotic physical properties due to a four-fold degenerate band crossing at the Y point of the Brillouin zone,which is protected by the nonsymmorphic symmetry of the space group.We carried out the heat capacity,electrical and thermal transport measurements on CrP and extracted the electron thermal conductivity.Due to the difference in energy and momentum relaxation time during electron-phonon inelastic scattering,the normalized Lorentz number decreases below about 160 K.Below 25.6 K,the normalized Lorentz number begins to recover,which is due to the dominance of elastic scattering between electrons and defects at low temperatures.展开更多
In this paper the influence of superconducting correlations on the thermal and charge conductances in a normal metal-superconductor （NS） junction in the clean limit is studied theoretically. First we solve the quasi...In this paper the influence of superconducting correlations on the thermal and charge conductances in a normal metal-superconductor （NS） junction in the clean limit is studied theoretically. First we solve the quasiclassical Eilenberger equations, and using the obtained density of states we can acquire the thermal and electrical conductances for the NS junction. Then we compare the conductance in a normal region of an NS junction with that in a single layer of normal metal （N）. Moreover, we study the Wiedemann-Franz （WF） law for these two cases （iN and NS）. From our calculations we conclude that the behaviour of the NS junction does not conform to the WF law for all temperatures. The effect of the thickness of normal metal on the thermal conductivity is also theoretically investigated in the paper.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2022YFA1403500)the National Science Foundation of China(Grant Nos.12004123,51861135104,and 11574097)+3 种基金the Fundamental Research Funds for the Central Universities(Grant No.2019kfy XMBZ071)supported by the Agence Nationale de la Recherche(Grant No.ANR-19-CE30-0014-04)the China National Postdoctoral Program for Innovative Talents(Grant No.BX20200143)the China Postdoctoral Science Foundation(Grant No.2020M682386)。
文摘We present a study of electrical and thermal transport in Weyl semimetal WTe_(2)down to 0.3 K.The Wiedemann-Franz law holds below 2 K and a downward deviation starts above.The deviation is more pronounced in cleaner samples,as expected in the hydrodynamic picture of electronic transport,where a fraction of electron-electron collisions conserve momentum.Phonons are the dominant heat carriers and their mean-free-path does not display a Knudsen minimum.This is presumably a consequence of weak anharmonicity,as indicated by the temperature dependence of the specific heat.Frequent momentum exchange between phonons and electrons leads to quantum oscillations of the phononic thermal conductivity.Bloch-Grüneisen picture of electron-phonon scattering breaks down at low temperature when Umklapp ph-ph collisions cease to be a sink for electronic flow of momentum.Comparison with semi-metallic Sb shows that normal ph-ph collisions are amplified by anharmonicity.In both semimetals,at cryogenic temperature,e-ph collisions degrade the phononic flow of energy but not the electronic flow of momentum.
基金supported by the National Natural Science Foundation of China(Grant Nos 50676046 and 50730006)
文摘The in-plane electrical and thermal conductivities of several polycrystalline platinum and gold nanofilms with different thicknesses are measured in a temperature range between the boiling point of liquid nitrogen （77K） and room temperature by using the direct current heating method. The result shows that both the electrical and thermal conductivities of the nanofilms reduce greatly compared with their corresponding bulk values. However, the electrical conductivity drop is considerably greater than the thermal conductivity drop, which indicates that the influence of the internal grain boundary on heat transport is different from that of charge transport, hence leading to the violation of the Wiedemann-Franz law. We build an electron relaxation model based on Matthiessen＇s rule to analyse the thermal conductivity and employ the Mayadas ＆ Shatzkes theory to analyse the electrical conductivity. Moreover, a modified Wiedemann-Franz law is provided in this paper, the obtained results from which are in good agreement with the experimental data.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12134018,11921004,and 11634015)the National Key Research and Development Program of China(Grant Nos.2022YFA1602800,2021YFA1401800,2017YFA0302901,2017YFA0302903,and 2022YFA1402203)+1 种基金the Strategic Priority Research Program and Key Research Program of Frontier Sciences of the Chinese Academy of Sciences(Grant No.XDB33010100)the Synergetic Extreme Condition User Facility(SECUF).
文摘CrP has many exotic physical properties due to a four-fold degenerate band crossing at the Y point of the Brillouin zone,which is protected by the nonsymmorphic symmetry of the space group.We carried out the heat capacity,electrical and thermal transport measurements on CrP and extracted the electron thermal conductivity.Due to the difference in energy and momentum relaxation time during electron-phonon inelastic scattering,the normalized Lorentz number decreases below about 160 K.Below 25.6 K,the normalized Lorentz number begins to recover,which is due to the dominance of elastic scattering between electrons and defects at low temperatures.
文摘In this paper the influence of superconducting correlations on the thermal and charge conductances in a normal metal-superconductor （NS） junction in the clean limit is studied theoretically. First we solve the quasiclassical Eilenberger equations, and using the obtained density of states we can acquire the thermal and electrical conductances for the NS junction. Then we compare the conductance in a normal region of an NS junction with that in a single layer of normal metal （N）. Moreover, we study the Wiedemann-Franz （WF） law for these two cases （iN and NS）. From our calculations we conclude that the behaviour of the NS junction does not conform to the WF law for all temperatures. The effect of the thickness of normal metal on the thermal conductivity is also theoretically investigated in the paper.
