To understand the relation between different nanostructures and thermal properties, a simple yet effective model is in demand for characterizing the underlying phonons and electrons scattering mechanisms. Herein, we m...To understand the relation between different nanostructures and thermal properties, a simple yet effective model is in demand for characterizing the underlying phonons and electrons scattering mechanisms. Herein, we make a systematic review on the newly developed thermal reffusivity theory. Like electrical resistivity which has been historically used as a theory for analyzing structural domain size and defect levels of metals, the thermal reffusivity can also uncover phonon behavior, structure defects and domain size of materials. We highlight that this new theory can be used for not only metals, but also nonmetals, even for amorphous materials. From the thermal reffusivity against temperature curves, the Debye temperature of the material and the ideal thermal diffusivity of single perfect crystal can be evaluated. From the residual thermal reffusivity at the 0 K limit, the structural thermal domain （STD） size of crystalline and amorphous materials can be obtained. The difference of white hair and normal black hair from heat conduction perspective is reported for the first time. Loss of melanin results in a worse thermal protection and a larger STD size in the white hair. By reviewing the different variation of thermal reffusivity against decreasing temperature profiles, we conclude that they reflected the structural connection in the materials. Ultimately, the future application of thermal reffusivity theory in studying 2D materials and amorphous materials is discussed.展开更多
Understanding the negative thermal expansion(NTE)mechanism is of great importance.In this work,we consider the new NTE compound Gd Fe(CN)_(6)(α_(v)=-34.2×10^(-6)K^(-1))as a case study to investigate the NTE mech...Understanding the negative thermal expansion(NTE)mechanism is of great importance.In this work,we consider the new NTE compound Gd Fe(CN)_(6)(α_(v)=-34.2×10^(-6)K^(-1))as a case study to investigate the NTE mechanism from the perspective of the lattice vibrational dynamics.The atomic mean-square displacements suggest that the NTE of Gd Fe(CN)_(6)comes from the strong tension effect induced by the transverse vibrations of the atomic-Fe-C≡N-Gd-linkages,with the largest contribution given by N atoms.Lattice dynamics calculations show that three low-frequency optical modes at about 50 cm^(-1)show the largest negative Grüneisen parameters thus providing the largest contribution to the NTE.The existence of these unusual low-frequency vibrational modes can be ascribed to the presence of GdN_(6)trigonal prisms in the framework structure of Gd Fe(CN)_(6).展开更多
A unique feature of transition metal dichalcogenides is their single-layer form, which enables folding. Although folding has been found to significantly affect the photoluminescence spectrum and some in-plane properti...A unique feature of transition metal dichalcogenides is their single-layer form, which enables folding. Although folding has been found to significantly affect the photoluminescence spectrum and some in-plane properties, only limited insight has been gained on how to modulate those properties. In this report, we examine the structure of folds of a single sheet of MoS2 and the dependence of the ground-s tate electronic and phonon transport properties on the wrapping length. As the folded structure is effectively a bilayer that terminates in a loop, the wrapping length modulates the relative size of the bilayer region to the closed loop along the edge. A combination of computational methods, including approaches based on variational mechanics, classical potentials, and density functional theory, are employed. Highly accurate calculations of the reference folded structure are first carried out to show that the folded structure is largely insensitive to the wrapping length. The folded structures are subsequently used to estimate the electronic band gap, which is found to vary significantly as a function of the wrapping length, and converges from below to the limit value corresponding to an infinite bilayer. The gap values range from 0.43 to 1.09 eV, with a crossover to an indirect gap, which suggests that the transitions must be lattice-assisted, similar to the transitions in the bilayer and bulk forms. However, the phonons, while affected by the formation of the folded structure, are insensitive to the wrapping length. In fact, the overall thermal transport behavior along the folding axis is unchanged. The possibility of modulating the gap value while keeping the thermal properties unchanged opens up new exciting avenues for further applications of this emerging material.展开更多
We study the relation between renormalization of the chemical potential due to multiphonon effects at the surface of Be（0001） and doping by solving the strong-coupling self-consistent equations of a two-dimensional...We study the relation between renormalization of the chemical potential due to multiphonon effects at the surface of Be（0001） and doping by solving the strong-coupling self-consistent equations of a two-dimensional（2D） electron-phonon interaction system.We present the quasiparticle dispersions and inverse lifetimes of a 2D electron system interacting with Einstein phonons under the different dopings（corresponding to chemical potentials）.We find that the effect of electron-phonon interaction on electron structure is strongest at the half filling,but it has no effect on the chemical potential.However,the chemical potential shows distinct renormalization effects away from half filling due to the electron-phonon interaction.展开更多
A quantum statistical theory of the superconductivity in MgB<sub>2</sub> is developed regarding it as a member of the graphite intercalation compound. The superconducting temperature T<sub>c</sub&...A quantum statistical theory of the superconductivity in MgB<sub>2</sub> is developed regarding it as a member of the graphite intercalation compound. The superconducting temperature T<sub>c</sub> for MgB<sub>2</sub>, C<sub>8</sub>K ≡ KC<sub>8</sub>, CaC<sub>6</sub>, are 39 K, 0.6 K, 11.5 K, respectively. The differences arise from the lattice structures. In the plane perpendicular to the c-axis, B’s form a honeycomb lattice with the nearest neighbour distance while Mg’s form a base-hexagonal lattice with the nearest neighbour distance above and below the B-plane distanced by . The more compact B-plane becomes superconducting due to the electron-phonon attraction. Starting with the generalized Bardeen- Cooper-Schrieffer (BCS) Hamiltonian and solving the generalized Cooper equation, we obtain a linear dispersion relation for moving Cooper pairs. The superconducting temperature T<sub>c</sub> identified as the Bose-Einstein condensation temperature of the Cooper pairs in two dimensions is given by , where is the Cooper pair density, the Boltzmann constant. The lattices of KC<sub>8</sub> and CaC<sub>6</sub> are clearly specified.展开更多
With the strong-field scheme and trigonal bases, the complete d3 energy matrix in a trigonally distorted cubic-field has been constructed. By diagonalizing this matrix, the energy spectrum of YGG：Cr^3＋ at normal pre...With the strong-field scheme and trigonal bases, the complete d3 energy matrix in a trigonally distorted cubic-field has been constructed. By diagonalizing this matrix, the energy spectrum of YGG：Cr^3＋ at normal pressure and low temperature has been calculated. The g factor of the ground-state has been evaluated in terms of the energy spectrum. At the same time, by using the wavefunctions obtained from diagonalizing the complete d^3 energy matrix and Thermal Shifts theory, we calculate the thermal shifts of the sharp lines of YGG：Cr^3＋ and determine the relevant parameters. The calculated results are all in good agreement with the optical-spectrum and EPR experimental data. It is demonstrated that the obtained wavefunctions and the values of parameters are reasonable.展开更多
Ballistic thermal transport properties in a cylindrical quantum structure modulated with double quantum dots(DQDs) are investigated.Results show that the transmission coefficients exhibit the irregular oscillation.Som...Ballistic thermal transport properties in a cylindrical quantum structure modulated with double quantum dots(DQDs) are investigated.Results show that the transmission coefficients exhibit the irregular oscillation.Some resonant transmission peaks and stop-frequency gaps can be observed,and the number and positions of these peaks and gaps are sensitive to the sizes of DQDs.With increasing the temperature,the thermal conductance undergoes a transition from the decrease to increase,and can be efficiently tuned by modulating the radius,length of DQDs as well as the interval between DQDs.In addition,at low temperatures,the enhancement of the thermal conductance can be also observed in this case.Some similarities and differences between the cylindrical and rectangular structures are identified.展开更多
文摘To understand the relation between different nanostructures and thermal properties, a simple yet effective model is in demand for characterizing the underlying phonons and electrons scattering mechanisms. Herein, we make a systematic review on the newly developed thermal reffusivity theory. Like electrical resistivity which has been historically used as a theory for analyzing structural domain size and defect levels of metals, the thermal reffusivity can also uncover phonon behavior, structure defects and domain size of materials. We highlight that this new theory can be used for not only metals, but also nonmetals, even for amorphous materials. From the thermal reffusivity against temperature curves, the Debye temperature of the material and the ideal thermal diffusivity of single perfect crystal can be evaluated. From the residual thermal reffusivity at the 0 K limit, the structural thermal domain （STD） size of crystalline and amorphous materials can be obtained. The difference of white hair and normal black hair from heat conduction perspective is reported for the first time. Loss of melanin results in a worse thermal protection and a larger STD size in the white hair. By reviewing the different variation of thermal reffusivity against decreasing temperature profiles, we conclude that they reflected the structural connection in the materials. Ultimately, the future application of thermal reffusivity theory in studying 2D materials and amorphous materials is discussed.
基金supported by the National Natural Science Foundation of China(Nos.22071221 and 21905252)the Natural Science Foundation of Henan Province(No.212300410086)Use of the Advanced Photon Source,an Office of Science User Facility operated for the U.S.Department of Energy(DOE)Office of Science by Argonne National Laboratory,was supported by the U.S.DOE under Contract No.DE-AC02-06CH11357。
文摘Understanding the negative thermal expansion(NTE)mechanism is of great importance.In this work,we consider the new NTE compound Gd Fe(CN)_(6)(α_(v)=-34.2×10^(-6)K^(-1))as a case study to investigate the NTE mechanism from the perspective of the lattice vibrational dynamics.The atomic mean-square displacements suggest that the NTE of Gd Fe(CN)_(6)comes from the strong tension effect induced by the transverse vibrations of the atomic-Fe-C≡N-Gd-linkages,with the largest contribution given by N atoms.Lattice dynamics calculations show that three low-frequency optical modes at about 50 cm^(-1)show the largest negative Grüneisen parameters thus providing the largest contribution to the NTE.The existence of these unusual low-frequency vibrational modes can be ascribed to the presence of GdN_(6)trigonal prisms in the framework structure of Gd Fe(CN)_(6).
文摘A unique feature of transition metal dichalcogenides is their single-layer form, which enables folding. Although folding has been found to significantly affect the photoluminescence spectrum and some in-plane properties, only limited insight has been gained on how to modulate those properties. In this report, we examine the structure of folds of a single sheet of MoS2 and the dependence of the ground-s tate electronic and phonon transport properties on the wrapping length. As the folded structure is effectively a bilayer that terminates in a loop, the wrapping length modulates the relative size of the bilayer region to the closed loop along the edge. A combination of computational methods, including approaches based on variational mechanics, classical potentials, and density functional theory, are employed. Highly accurate calculations of the reference folded structure are first carried out to show that the folded structure is largely insensitive to the wrapping length. The folded structures are subsequently used to estimate the electronic band gap, which is found to vary significantly as a function of the wrapping length, and converges from below to the limit value corresponding to an infinite bilayer. The gap values range from 0.43 to 1.09 eV, with a crossover to an indirect gap, which suggests that the transitions must be lattice-assisted, similar to the transitions in the bilayer and bulk forms. However, the phonons, while affected by the formation of the folded structure, are insensitive to the wrapping length. In fact, the overall thermal transport behavior along the folding axis is unchanged. The possibility of modulating the gap value while keeping the thermal properties unchanged opens up new exciting avenues for further applications of this emerging material.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10574063)
文摘We study the relation between renormalization of the chemical potential due to multiphonon effects at the surface of Be（0001） and doping by solving the strong-coupling self-consistent equations of a two-dimensional（2D） electron-phonon interaction system.We present the quasiparticle dispersions and inverse lifetimes of a 2D electron system interacting with Einstein phonons under the different dopings（corresponding to chemical potentials）.We find that the effect of electron-phonon interaction on electron structure is strongest at the half filling,but it has no effect on the chemical potential.However,the chemical potential shows distinct renormalization effects away from half filling due to the electron-phonon interaction.
文摘A quantum statistical theory of the superconductivity in MgB<sub>2</sub> is developed regarding it as a member of the graphite intercalation compound. The superconducting temperature T<sub>c</sub> for MgB<sub>2</sub>, C<sub>8</sub>K ≡ KC<sub>8</sub>, CaC<sub>6</sub>, are 39 K, 0.6 K, 11.5 K, respectively. The differences arise from the lattice structures. In the plane perpendicular to the c-axis, B’s form a honeycomb lattice with the nearest neighbour distance while Mg’s form a base-hexagonal lattice with the nearest neighbour distance above and below the B-plane distanced by . The more compact B-plane becomes superconducting due to the electron-phonon attraction. Starting with the generalized Bardeen- Cooper-Schrieffer (BCS) Hamiltonian and solving the generalized Cooper equation, we obtain a linear dispersion relation for moving Cooper pairs. The superconducting temperature T<sub>c</sub> identified as the Bose-Einstein condensation temperature of the Cooper pairs in two dimensions is given by , where is the Cooper pair density, the Boltzmann constant. The lattices of KC<sub>8</sub> and CaC<sub>6</sub> are clearly specified.
基金supported by National Natural Science Foundation of China under Grant No.10775102
文摘With the strong-field scheme and trigonal bases, the complete d3 energy matrix in a trigonally distorted cubic-field has been constructed. By diagonalizing this matrix, the energy spectrum of YGG：Cr^3＋ at normal pressure and low temperature has been calculated. The g factor of the ground-state has been evaluated in terms of the energy spectrum. At the same time, by using the wavefunctions obtained from diagonalizing the complete d^3 energy matrix and Thermal Shifts theory, we calculate the thermal shifts of the sharp lines of YGG：Cr^3＋ and determine the relevant parameters. The calculated results are all in good agreement with the optical-spectrum and EPR experimental data. It is demonstrated that the obtained wavefunctions and the values of parameters are reasonable.
基金supported by the National Natural Science Foundation of China (Grant No.11204074)
文摘Ballistic thermal transport properties in a cylindrical quantum structure modulated with double quantum dots(DQDs) are investigated.Results show that the transmission coefficients exhibit the irregular oscillation.Some resonant transmission peaks and stop-frequency gaps can be observed,and the number and positions of these peaks and gaps are sensitive to the sizes of DQDs.With increasing the temperature,the thermal conductance undergoes a transition from the decrease to increase,and can be efficiently tuned by modulating the radius,length of DQDs as well as the interval between DQDs.In addition,at low temperatures,the enhancement of the thermal conductance can be also observed in this case.Some similarities and differences between the cylindrical and rectangular structures are identified.
