The atomistic Green’s function method is improved to compute the polarization resolved phonon transport in a multiterminal system. Based on the recent developments in literature, the algorithm is simplified. The comp...The atomistic Green’s function method is improved to compute the polarization resolved phonon transport in a multiterminal system. Based on the recent developments in literature, the algorithm is simplified. The complex phonon band structure of a semi-infinite periodic terminal is obtained by the generalized eigenvalue equation. Then both the surface Green’s function and phonon group velocity in the terminal are determined from the wave modes propagating away from the scattering region along the terminal. With these key ingredients, the individual phonon mode transmittance between the terminals can be calculated. The feasibility and validity of the method are demonstrated by the chain example compared with the wave packet method, and an example of graphene nanojunction with three terminals.展开更多
Accurate prediction of junction temperature is crucial for the efficient thermal design of silicon nano-devices. In nano-scale semiconductor devices, significant ballistic effects occur due to the mean free path of ph...Accurate prediction of junction temperature is crucial for the efficient thermal design of silicon nano-devices. In nano-scale semiconductor devices, significant ballistic effects occur due to the mean free path of phonons comparable to the heat source size and device scale. We employ a three-dimensional non-gray Monte Carlo simulation to investigate the transient heat conduction of silicon nanofilms with both single and multiple heat sources. The accuracy of the present method is first verified in the ballistic and diffusion limits. When a single local heat source is present, the width of the heat source has a significant impact on heat conduction in the domain. Notably, there is a substantial temperature jump at the boundary when the heat source width is 10 nm.With increasing heat source width, the boundary temperature jump weakens. Furthermore, we observe that the temperature excitation rate is independent of the heat source width, while the temperature influence range expands simultaneously with the increase in heat source width. Around 500 ps, the temperature and heat flux distribution in the domain stabilize. In the case of dual heat sources, the hot zone is broader than that of a single heat source, and the temperature of the hot spot decreases as the heat source spacing increases. However, the mean heat flux remains unaffected. Upon reaching a spacing of 200 nm between the heat sources, the peak temperature in the domain remains unchanged once a steady state is reached. These findings hold significant implications for the thermal design of silicon nano-devices with local heat sources.展开更多
Stacking faults(SFs)are often present in silicon carbide(SiC)and affect its thermal and heat-transport properties.However,it is unclear how SFs influence thermal transport.Using non-equilibrium molecular dynamics and ...Stacking faults(SFs)are often present in silicon carbide(SiC)and affect its thermal and heat-transport properties.However,it is unclear how SFs influence thermal transport.Using non-equilibrium molecular dynamics and lattice dynamics simulations,we studied phonon transport in SiC materials with an SF.Compared to perfect SiC materials,the SF can reduce thermal conductivity.This is caused by the additional interface thermal resistance(ITR)of SF,which is difficult to capture by the previous phenomenological models.By analyzing the spectral heat flux,we find that SF reduces the contribution of low-frequency(7.5 THz-12 THz)phonons to the heat flux,which can be attributed to SF reducing the phonon lifetime and group velocity,especially in the low-frequency range.The SF hinders phonon transport and results in an effective interface thermal resistance around the SF.Our results provide insight into the microscopic mechanism of the effect of defects on heat transport and have guiding significance for the regulation of the thermal conductivity of materials.展开更多
It has now become recognized that the electron-phonon coupling(EPC)may play an important role in governing the phonon transport,especially for metallic and semiconducting systems at high carrier concentration.Here we ...It has now become recognized that the electron-phonon coupling(EPC)may play an important role in governing the phonon transport,especially for metallic and semiconducting systems at high carrier concentration.Here we focus on the Weyl semimetals TaAs and NbAs and give a comparative study on their phonon transport properties by explicitly including the EPC in first-principles calculations.It is found that the lattice thermal conductivities of both systems are significantly reduced by the EPC,which is more pronounced for the TaAs compared with the NbAs at the same carrier concentration.Detailed analysis indicates that the TaAs exhibits smaller EPC phonon relaxation time,as characterized by stronger EPC strength which is associated with larger deformation potential constant and Born effective charge.Moreover,we see that the TaAs exhibits obviously larger overlap between the EPC relaxation time and that from intrinsic phonon-phonon scattering,which could further reduce the lattice thermal conduc-tivity.Our work not only highlights the vital importance of EPC in accurately predicting the phonon transport behaviors,but also offers a simple alternative to evaluate the EPC strength of various material systems.展开更多
Recently,PbSnSe_(2)alloy was found to exhibit a large hysteresis effect on transport properties,demonstrating its significant potential for thermoelectric applications.Using ab initio approaches,we studied the carrier...Recently,PbSnSe_(2)alloy was found to exhibit a large hysteresis effect on transport properties,demonstrating its significant potential for thermoelectric applications.Using ab initio approaches,we studied the carrier transport properties of PbSnSe_(2)crystal,which is a special case of the alloy with the shortest-range order.A peak power factor of 134.2μW cm^(-1)K^(-2)was found along the crossplane direction in the n-type PbSnSe_(2)at a doping concentration of 7×10^(20)cm^(-3)at 700 K.This high power factor originates from delocalized p electrons between intra-plane Pb-Se pairs and between cross-plane Sn-Se pairs that can build up transport channels for conducting electrons,leading to a high electrical conductivity of 5.9×10^(5)S m^(-1).Introducing Pb atoms into Pnma phase SnSe can decrease the phonon group velocities and enhance the phonon-phonon scatterings,leading to a low thermal conductivity of 0.53 W m^(-1)K^(-1)at 700 K along the cross-plane direction.The calculated peak ZT of~3 along the cross-plane direction at an n-type doping concentration of around 5×10^(19)cm^(-3),which represents a theoretical upper limit for an idealized PbSnSe_(2)crystal.This work interprets the origins of three-dimensional charge and two-dimensional phonon transport behavior in PbSnSe_(2)and demonstrates that such crystals are promising high-performance thermoelectric semiconductors.展开更多
The combination of different nanostructures can hinder phonons transmission in a wide frequency range and further reduce the thermal conductivity(TC).This will benefit the improvement and application of thermoelectric...The combination of different nanostructures can hinder phonons transmission in a wide frequency range and further reduce the thermal conductivity(TC).This will benefit the improvement and application of thermoelectric conversion,insulating materials and thermal barrier coatings,etc.In this work,the effects of nanopillars and Ge nanoparticles(GNPs)on the thermal transport of Si nanowire(SN)are investigated by nonequilibrium molecular dynamics(NEMD)simulation.By analyzing phonons transport behaviors,it is confirmed that the introduction of nanopillars leads to the occurrence of lowfrequency phonons resonance,and nanoparticles enhance high-frequency phonons interface scattering and localization.The results show that phonons transport in the whole frequency range can be strongly hindered by the simultaneous introduction of nanopillars and nanoparticles.In addition,the effects of system length,temperature,sizes and numbers of nanoparticles on the TC are investigated.Our work provides useful insights into the effective regulation of the TC of nanomaterials.展开更多
The coherent potential approximation(CPA)within full counting statistics(FCS)formalism is shown to be a suitable method to investigate average electric conductance,shot noise as well as higher order cumulants in disor...The coherent potential approximation(CPA)within full counting statistics(FCS)formalism is shown to be a suitable method to investigate average electric conductance,shot noise as well as higher order cumulants in disordered systems.We develop a similar FCS-CPA formalism for phonon transport through disordered systems.As a byproduct,we derive relations among coefficients of different phonon current cumulants.We apply the FCS-CPA method to investigate phonon transport properties of graphene systems in the presence of disorders.For binary disorders as well as Anderson disorders,we calculate up to the 8-th phonon transmission moments and demonstrate that the numerical results of the FCS-CPA method agree very well with that of the brute force method.The benchmark shows that the FCS-CPA method achieves 20 times more speedup ratio.Collective features of phonon current cumulants are also revealed.展开更多
We report a theoretical investigation of coherent-to-incoherent heat conduction in multilayer nanostructures.In the coherent regime where the phonon motion is quasi-harmonic,the elastic continuum model gives accurate ...We report a theoretical investigation of coherent-to-incoherent heat conduction in multilayer nanostructures.In the coherent regime where the phonon motion is quasi-harmonic,the elastic continuum model gives accurate cross-plane thermal conductivity predictions of upper limits and demonstrates that the coherent transport is the result of the interplay between intrinsic wave effects.As the temperature or system size increases,the phonon dephasing scattering results in the deviation of thermal conductivity from the coherent-limit calculation.By further introducing the incoherence of phonons,we reproduce the classical minimum thermal conductivity,indicating the feasibility of extending the pure wave model into the wave-particle crossing regime.展开更多
The heat conduction and thermal conductivity for methane hydrate are simulated from equilibrium molecular dynamics. The thermal conductivity and temperature dependence trend agree well with the experimental results. T...The heat conduction and thermal conductivity for methane hydrate are simulated from equilibrium molecular dynamics. The thermal conductivity and temperature dependence trend agree well with the experimental results. The nonmonotonic temperature dependence is attributed to the phonon inelastic scattering at higher temperature and to the confinement of the optic phonon modes and low frequency phonons at low temperature. The thermal conductivity scales proportionally with the van der Waals interaction strength, The conversion of a crystal-like nature into an amorphous one oecurs at higher strength. Both the temperature dependence and interaction strength dependence are explained by phonon inelastic scattering.展开更多
Electronic transport through a vibrating double quantum dot (DQD) in contact with noncollinear ferromagnetic (FM) leads is investigated. The state transition between the two dots of the DQD is excited by an AC mic...Electronic transport through a vibrating double quantum dot (DQD) in contact with noncollinear ferromagnetic (FM) leads is investigated. The state transition between the two dots of the DQD is excited by an AC microwave driving field. The corresponding currents and differential conductance are calculated in the Coulomb blockade regime by means of the Born-Markov master equation. It is shown that the interplay between electrons and phonons gives rise to phonon-assisted tunneling resonances and Franck-Condon blockade under certain conditions. In noncollinear magnetic configurations, spin-blockade effects are also observed, and the angle of polarization has some influence on the transport characteristics.展开更多
The influence of electron-phonon (EP) scattering on spin polarization of current output from a mesoscopic ring with Rashba spin-orbit (SO) interaction is numerically investigated. There are three leads connecting ...The influence of electron-phonon (EP) scattering on spin polarization of current output from a mesoscopic ring with Rashba spin-orbit (SO) interaction is numerically investigated. There are three leads connecting to the ring at different positionsl unpolarized current is injected to one of them, and the other two are output channels with different bias voltages. The spin polarization of current in the outgoing leads shows oscillations as a function of EP coupling strength owing to the quantum interference of EP states in the ring region. As temperature increases, the oscillations are evidently suppressed, implying decoherence of the EP states. The simulation shows that the magnitude of polarized current is sensitive to the location of the lead. The polarized current depends on the connecting position of the lead in a complicated way due to the spin-sensitive quantum interference effects caused by different phases accumulated by transmitting electrons with opposite spin states along different paths.展开更多
Using the elastic wave continuum model, we investigate the effect of material properties on ballistic thermal transport in a cylindrical nanowire. A comparative analysis for the convexity-shaped and concavity-shaped s...Using the elastic wave continuum model, we investigate the effect of material properties on ballistic thermal transport in a cylindrical nanowire. A comparative analysis for the convexity-shaped and concavity-shaped structure is made. It is found that in the convexity-shaped structure, the material with higher wave velocity in the convexity region can increase the thermal conductance at the lower temperature range; the thermal conductance of the nanowire with higher wave velocity in the convexity region is lower than that of the nanowire with lower wave velocity in the convexity region at the higher temperature range. However, in the concavity-shaped structure, the material properties of the concavity region have less effect on the thermal conductance at the lower temperature range; the material with higher wave velocity in the concavity region can reduce the thermal conductance at the higher temperature range. A brief analysis of these results is given.展开更多
We propose the concept of thermal demultiplexer, which can split the heat flux in different frequency ranges intodifferent directions. We demonstrate this device concept in a honeycomb lattice with dangling atoms. Fro...We propose the concept of thermal demultiplexer, which can split the heat flux in different frequency ranges intodifferent directions. We demonstrate this device concept in a honeycomb lattice with dangling atoms. From the view ofeffective negative mass, we give a qualitative explanation of how the dangling atoms change the original transport property.We first design a two-mass configuration thermal demultiplexer, and find that the heat flux can flow into different ports incorresponding frequency ranges roughly. Then, to improve the performance, we choose the suitable masses of danglingatoms and optimize the four-mass configuration with genetic algorithm. Finally, we give out the optimal configuration witha remarkable effect. Our study finds a way to selectively split spectrum-resolved heat to different ports as phonon splitter,which would provide a new means to manipulate phonons and heat, and to guide the design of phononic thermal devices inthe future.展开更多
One of the abundantly available energies that could be found in industrial power plants, running vehicles, nuclear power stations, etc. is known as thermal energy. A physical phenomenon known as thermoelectricity conv...One of the abundantly available energies that could be found in industrial power plants, running vehicles, nuclear power stations, etc. is known as thermal energy. A physical phenomenon known as thermoelectricity converts thermal energy into electrical energy and vice versa, providing a green route for power generation and a potential solution to the world energy crisis. The thermoelectric conversion efficiency is generally characterized by the temperature-dependent dimensionless figure of merit(zT), which is generally promoted by increasing the power factor and reducing the thermal conductivity. The present work reviews heat transmission in thermoelectric materials, particularly phonon engineering to reduce the lattice thermal conductivity. The two leading strategies of point defects engineering and nanostructuring for reducing thermal conductivity have been summarized. The optimized reported zTs of various thermoelectric materials in terms of reduced thermal conductivity have been presented.展开更多
We propose an optimized scheme to determine the smearing parameter in the Gaussian function that is used to replace the Dirac δ function in the first Brillouin zone sampling. The broadening width is derived by analyz...We propose an optimized scheme to determine the smearing parameter in the Gaussian function that is used to replace the Dirac δ function in the first Brillouin zone sampling. The broadening width is derived by analyzing the difference of the results from the phase-space method and Gaussian broadening method. As a demonstration, using the present approach,we investigate the phonon transport in a typical layered material, graphite. Our scheme is benchmarked by comparing with other zone sampling methods. Both the three-phonon phonon scattering rates and thermal conductivity are consistent with the prediction from the widely used tetrahedron method and adaptive broadening method. The computational efficiency of our scheme is more than one order of magnitude higher than the two other methods. Furthermore, the effect of fourphonon scattering in phonon transport in graphite is also investigated. It is found that four-phonon scattering reduces the through-plane thermal conductivity by 10%. Our methods could be a reference for the prediction of thermal conductivity of anisotropic material in the future.展开更多
The dynamical process of charge injection from metal electrode to a nondegenerate polymer in a metal/polythiophene (PT)/metal structure has been investigated by using a nonadiabatic dynamic approach. It is found tha...The dynamical process of charge injection from metal electrode to a nondegenerate polymer in a metal/polythiophene (PT)/metal structure has been investigated by using a nonadiabatic dynamic approach. It is found that the injected charges form wave packets due to the strong electron-lattice interaction in PT. We demonstrate that the dynamical formation of the wave packet sensitively depends on the strength of applied voltage, the electric field, and the contact between PT and electrode. At a strength of the electric field more than 3.0 × 10^4 V/cm, the carriers can be ejected from the PT into the right electrode. At an electric field more than 3.0 × 10^5 V/cm, the wave packet cannot form while it moves rapidly to the right PT/metal interface. It is shown that the ejected quantity of charge is noninteger.展开更多
Tin monoxide(SnO) is an interesting two-dimensional material because it is a rare oxide semiconductor with bipolar conductivity.However, the lower room temperature mobility limits the applications of SnO in the future...Tin monoxide(SnO) is an interesting two-dimensional material because it is a rare oxide semiconductor with bipolar conductivity.However, the lower room temperature mobility limits the applications of SnO in the future.Thus, we systematically investigate the effects of different layer structures and strains on the electron–phonon coupling and phonon-limited mobility of SnO.The A2uphonon mode in the high-frequency region is the main contributor to the coupling with electrons for different layer structures.Moreover, the orbital hybridization of Sn atoms existing only in the bilayer structure changes the conduction band edge and conspicuously decreases the electron–phonon coupling, and thus the electronic transport performance of the bilayer is superior to that of other layers.In addition, the compressive strain of ε=-1.0% in the monolayer structure results in a conduction band minimum(CBM) consisting of two valleys at the Γ point and along the M–Γ line, and also leads to the intervalley electronic scattering assisted by the Eg(-1)mode.However, the electron–phonon coupling regionally transferring from high frequency A2uto low frequency Eg(-1)results in little change of mobility.展开更多
Phonon-assisted tunneling (PhAT) model is applied for explication of temperature-dependent conductivity and I-V characteristics measured by various investigators for graphene nanoribbons and oxides ones. Proposed mode...Phonon-assisted tunneling (PhAT) model is applied for explication of temperature-dependent conductivity and I-V characteristics measured by various investigators for graphene nanoribbons and oxides ones. Proposed model describes well not only current dependence on temperature but also the temperature-dependent I-V data using the same set of parameters characterizing material under investigation. The values of active phonons energy and field strength for tunneling are estimated from the fit of current dependence on temperature and I-V/T data with the phonon-assisted tunneling theory.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.51376094)Jiangsu Overseas Visiting Scholar Program for University Prominent Young&Middle-aged Teachers and Presidents,China
文摘The atomistic Green’s function method is improved to compute the polarization resolved phonon transport in a multiterminal system. Based on the recent developments in literature, the algorithm is simplified. The complex phonon band structure of a semi-infinite periodic terminal is obtained by the generalized eigenvalue equation. Then both the surface Green’s function and phonon group velocity in the terminal are determined from the wave modes propagating away from the scattering region along the terminal. With these key ingredients, the individual phonon mode transmittance between the terminals can be calculated. The feasibility and validity of the method are demonstrated by the chain example compared with the wave packet method, and an example of graphene nanojunction with three terminals.
基金supported by the National Natural Science Foundation of China (Grant No. 52076088)the Core Technology Research Project of Shunde District, Foshan, China (Grant No. 2130218002932)。
文摘Accurate prediction of junction temperature is crucial for the efficient thermal design of silicon nano-devices. In nano-scale semiconductor devices, significant ballistic effects occur due to the mean free path of phonons comparable to the heat source size and device scale. We employ a three-dimensional non-gray Monte Carlo simulation to investigate the transient heat conduction of silicon nanofilms with both single and multiple heat sources. The accuracy of the present method is first verified in the ballistic and diffusion limits. When a single local heat source is present, the width of the heat source has a significant impact on heat conduction in the domain. Notably, there is a substantial temperature jump at the boundary when the heat source width is 10 nm.With increasing heat source width, the boundary temperature jump weakens. Furthermore, we observe that the temperature excitation rate is independent of the heat source width, while the temperature influence range expands simultaneously with the increase in heat source width. Around 500 ps, the temperature and heat flux distribution in the domain stabilize. In the case of dual heat sources, the hot zone is broader than that of a single heat source, and the temperature of the hot spot decreases as the heat source spacing increases. However, the mean heat flux remains unaffected. Upon reaching a spacing of 200 nm between the heat sources, the peak temperature in the domain remains unchanged once a steady state is reached. These findings hold significant implications for the thermal design of silicon nano-devices with local heat sources.
基金Sichuan Science and Technology Program(Grant No.2023NSFSC0044)the National Natural Science Foundation of China(Grant No.51501119)+1 种基金the Fundamental Research Funds for the Central Universitiespartially supported by the High-Performance Computing Center at Sichuan University。
文摘Stacking faults(SFs)are often present in silicon carbide(SiC)and affect its thermal and heat-transport properties.However,it is unclear how SFs influence thermal transport.Using non-equilibrium molecular dynamics and lattice dynamics simulations,we studied phonon transport in SiC materials with an SF.Compared to perfect SiC materials,the SF can reduce thermal conductivity.This is caused by the additional interface thermal resistance(ITR)of SF,which is difficult to capture by the previous phenomenological models.By analyzing the spectral heat flux,we find that SF reduces the contribution of low-frequency(7.5 THz-12 THz)phonons to the heat flux,which can be attributed to SF reducing the phonon lifetime and group velocity,especially in the low-frequency range.The SF hinders phonon transport and results in an effective interface thermal resistance around the SF.Our results provide insight into the microscopic mechanism of the effect of defects on heat transport and have guiding significance for the regulation of the thermal conductivity of materials.
基金support from the National Natural Science Foundation(Grant Nos.62074114,51772220).
文摘It has now become recognized that the electron-phonon coupling(EPC)may play an important role in governing the phonon transport,especially for metallic and semiconducting systems at high carrier concentration.Here we focus on the Weyl semimetals TaAs and NbAs and give a comparative study on their phonon transport properties by explicitly including the EPC in first-principles calculations.It is found that the lattice thermal conductivities of both systems are significantly reduced by the EPC,which is more pronounced for the TaAs compared with the NbAs at the same carrier concentration.Detailed analysis indicates that the TaAs exhibits smaller EPC phonon relaxation time,as characterized by stronger EPC strength which is associated with larger deformation potential constant and Born effective charge.Moreover,we see that the TaAs exhibits obviously larger overlap between the EPC relaxation time and that from intrinsic phonon-phonon scattering,which could further reduce the lattice thermal conduc-tivity.Our work not only highlights the vital importance of EPC in accurately predicting the phonon transport behaviors,but also offers a simple alternative to evaluate the EPC strength of various material systems.
基金National Key Research and Development Program of China,Grant/Award Number:2022YFB3803900National Natural Science Foundation of China,Grant/Award Number:52076089。
文摘Recently,PbSnSe_(2)alloy was found to exhibit a large hysteresis effect on transport properties,demonstrating its significant potential for thermoelectric applications.Using ab initio approaches,we studied the carrier transport properties of PbSnSe_(2)crystal,which is a special case of the alloy with the shortest-range order.A peak power factor of 134.2μW cm^(-1)K^(-2)was found along the crossplane direction in the n-type PbSnSe_(2)at a doping concentration of 7×10^(20)cm^(-3)at 700 K.This high power factor originates from delocalized p electrons between intra-plane Pb-Se pairs and between cross-plane Sn-Se pairs that can build up transport channels for conducting electrons,leading to a high electrical conductivity of 5.9×10^(5)S m^(-1).Introducing Pb atoms into Pnma phase SnSe can decrease the phonon group velocities and enhance the phonon-phonon scatterings,leading to a low thermal conductivity of 0.53 W m^(-1)K^(-1)at 700 K along the cross-plane direction.The calculated peak ZT of~3 along the cross-plane direction at an n-type doping concentration of around 5×10^(19)cm^(-3),which represents a theoretical upper limit for an idealized PbSnSe_(2)crystal.This work interprets the origins of three-dimensional charge and two-dimensional phonon transport behavior in PbSnSe_(2)and demonstrates that such crystals are promising high-performance thermoelectric semiconductors.
基金Project supported by the National Natural Science Foundation of China (Grant No.52076080)the Natural Science Foundation of Hebei Province of China (Grant No.E2020502011)。
文摘The combination of different nanostructures can hinder phonons transmission in a wide frequency range and further reduce the thermal conductivity(TC).This will benefit the improvement and application of thermoelectric conversion,insulating materials and thermal barrier coatings,etc.In this work,the effects of nanopillars and Ge nanoparticles(GNPs)on the thermal transport of Si nanowire(SN)are investigated by nonequilibrium molecular dynamics(NEMD)simulation.By analyzing phonons transport behaviors,it is confirmed that the introduction of nanopillars leads to the occurrence of lowfrequency phonons resonance,and nanoparticles enhance high-frequency phonons interface scattering and localization.The results show that phonons transport in the whole frequency range can be strongly hindered by the simultaneous introduction of nanopillars and nanoparticles.In addition,the effects of system length,temperature,sizes and numbers of nanoparticles on the TC are investigated.Our work provides useful insights into the effective regulation of the TC of nanomaterials.
基金the National Natural Science Foundation of China(Grant No.12034014)the Natural Science Foundation of Guangdong Province(Grant No.2020A1515011418).
文摘The coherent potential approximation(CPA)within full counting statistics(FCS)formalism is shown to be a suitable method to investigate average electric conductance,shot noise as well as higher order cumulants in disordered systems.We develop a similar FCS-CPA formalism for phonon transport through disordered systems.As a byproduct,we derive relations among coefficients of different phonon current cumulants.We apply the FCS-CPA method to investigate phonon transport properties of graphene systems in the presence of disorders.For binary disorders as well as Anderson disorders,we calculate up to the 8-th phonon transmission moments and demonstrate that the numerical results of the FCS-CPA method agree very well with that of the brute force method.The benchmark shows that the FCS-CPA method achieves 20 times more speedup ratio.Collective features of phonon current cumulants are also revealed.
文摘We report a theoretical investigation of coherent-to-incoherent heat conduction in multilayer nanostructures.In the coherent regime where the phonon motion is quasi-harmonic,the elastic continuum model gives accurate cross-plane thermal conductivity predictions of upper limits and demonstrates that the coherent transport is the result of the interplay between intrinsic wave effects.As the temperature or system size increases,the phonon dephasing scattering results in the deviation of thermal conductivity from the coherent-limit calculation.By further introducing the incoherence of phonons,we reproduce the classical minimum thermal conductivity,indicating the feasibility of extending the pure wave model into the wave-particle crossing regime.
基金Supported by the National Natural Science Foundation of China under Grant Nos U1262112 and 51176205
文摘The heat conduction and thermal conductivity for methane hydrate are simulated from equilibrium molecular dynamics. The thermal conductivity and temperature dependence trend agree well with the experimental results. The nonmonotonic temperature dependence is attributed to the phonon inelastic scattering at higher temperature and to the confinement of the optic phonon modes and low frequency phonons at low temperature. The thermal conductivity scales proportionally with the van der Waals interaction strength, The conversion of a crystal-like nature into an amorphous one oecurs at higher strength. Both the temperature dependence and interaction strength dependence are explained by phonon inelastic scattering.
基金Project supported by the National Natural Science Foundation of China(Grant No.61275059)
文摘Electronic transport through a vibrating double quantum dot (DQD) in contact with noncollinear ferromagnetic (FM) leads is investigated. The state transition between the two dots of the DQD is excited by an AC microwave driving field. The corresponding currents and differential conductance are calculated in the Coulomb blockade regime by means of the Born-Markov master equation. It is shown that the interplay between electrons and phonons gives rise to phonon-assisted tunneling resonances and Franck-Condon blockade under certain conditions. In noncollinear magnetic configurations, spin-blockade effects are also observed, and the angle of polarization has some influence on the transport characteristics.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 10474033 and 60676056)the State Key Projects of Basic Research of China (Grant Nos 2006CB0L1000 and 2005CB623605)
文摘The influence of electron-phonon (EP) scattering on spin polarization of current output from a mesoscopic ring with Rashba spin-orbit (SO) interaction is numerically investigated. There are three leads connecting to the ring at different positionsl unpolarized current is injected to one of them, and the other two are output channels with different bias voltages. The spin polarization of current in the outgoing leads shows oscillations as a function of EP coupling strength owing to the quantum interference of EP states in the ring region. As temperature increases, the oscillations are evidently suppressed, implying decoherence of the EP states. The simulation shows that the magnitude of polarized current is sensitive to the location of the lead. The polarized current depends on the connecting position of the lead in a complicated way due to the spin-sensitive quantum interference effects caused by different phases accumulated by transmitting electrons with opposite spin states along different paths.
基金Project supported by the National Natural Science Foundation of China(Grant No.11404110)the Natural Science Foundation of Hunan Province+5 种基金China(Grant Nos.14JJ31392015JJ6027and 2015JJ6030)the Outstanding Young Program from the Education Department of Hunan ProvinceChina(Grant No.14B046)the Doctoral Activation Foundation of Hunan Institute of Technology of China(Grant No.HQ14006)
文摘Using the elastic wave continuum model, we investigate the effect of material properties on ballistic thermal transport in a cylindrical nanowire. A comparative analysis for the convexity-shaped and concavity-shaped structure is made. It is found that in the convexity-shaped structure, the material with higher wave velocity in the convexity region can increase the thermal conductance at the lower temperature range; the thermal conductance of the nanowire with higher wave velocity in the convexity region is lower than that of the nanowire with lower wave velocity in the convexity region at the higher temperature range. However, in the concavity-shaped structure, the material properties of the concavity region have less effect on the thermal conductance at the lower temperature range; the material with higher wave velocity in the concavity region can reduce the thermal conductance at the higher temperature range. A brief analysis of these results is given.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11935010 and 11775159)the Shanghai Science and Technology Committee,China(Grant Nos.18ZR1442800 and 18JC1410900)the Opening Project of Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology.
文摘We propose the concept of thermal demultiplexer, which can split the heat flux in different frequency ranges intodifferent directions. We demonstrate this device concept in a honeycomb lattice with dangling atoms. From the view ofeffective negative mass, we give a qualitative explanation of how the dangling atoms change the original transport property.We first design a two-mass configuration thermal demultiplexer, and find that the heat flux can flow into different ports incorresponding frequency ranges roughly. Then, to improve the performance, we choose the suitable masses of danglingatoms and optimize the four-mass configuration with genetic algorithm. Finally, we give out the optimal configuration witha remarkable effect. Our study finds a way to selectively split spectrum-resolved heat to different ports as phonon splitter,which would provide a new means to manipulate phonons and heat, and to guide the design of phononic thermal devices inthe future.
基金Sponsored by the Shenzhen Science and Technology Program (Grant No.KQTD20200820113045081)the National Natural Science Foundation of China (Grant Nos.52172194, 51971081)+2 种基金the National Natural Science Foundation of China (Grant No.52101248)the Natural Science Foundation for Distinguished Young Scholars of Guangdong Province of China (Grant No.2020B1515020023)the Shenzhen Fundamental Research Projects (Grant No.JCYJ20210324132808020)。
文摘One of the abundantly available energies that could be found in industrial power plants, running vehicles, nuclear power stations, etc. is known as thermal energy. A physical phenomenon known as thermoelectricity converts thermal energy into electrical energy and vice versa, providing a green route for power generation and a potential solution to the world energy crisis. The thermoelectric conversion efficiency is generally characterized by the temperature-dependent dimensionless figure of merit(zT), which is generally promoted by increasing the power factor and reducing the thermal conductivity. The present work reviews heat transmission in thermoelectric materials, particularly phonon engineering to reduce the lattice thermal conductivity. The two leading strategies of point defects engineering and nanostructuring for reducing thermal conductivity have been summarized. The optimized reported zTs of various thermoelectric materials in terms of reduced thermal conductivity have been presented.
基金support from the National Natural Science Foundation of China (Grant No. 51706134)。
文摘We propose an optimized scheme to determine the smearing parameter in the Gaussian function that is used to replace the Dirac δ function in the first Brillouin zone sampling. The broadening width is derived by analyzing the difference of the results from the phase-space method and Gaussian broadening method. As a demonstration, using the present approach,we investigate the phonon transport in a typical layered material, graphite. Our scheme is benchmarked by comparing with other zone sampling methods. Both the three-phonon phonon scattering rates and thermal conductivity are consistent with the prediction from the widely used tetrahedron method and adaptive broadening method. The computational efficiency of our scheme is more than one order of magnitude higher than the two other methods. Furthermore, the effect of fourphonon scattering in phonon transport in graphite is also investigated. It is found that four-phonon scattering reduces the through-plane thermal conductivity by 10%. Our methods could be a reference for the prediction of thermal conductivity of anisotropic material in the future.
基金Project supported by the State Key Program of National Natural Science of China (Grant Nos 10474056 and 10574082)the Natural Science Foundation of Shandong Province (Grant No Z2005A01)
文摘The dynamical process of charge injection from metal electrode to a nondegenerate polymer in a metal/polythiophene (PT)/metal structure has been investigated by using a nonadiabatic dynamic approach. It is found that the injected charges form wave packets due to the strong electron-lattice interaction in PT. We demonstrate that the dynamical formation of the wave packet sensitively depends on the strength of applied voltage, the electric field, and the contact between PT and electrode. At a strength of the electric field more than 3.0 × 10^4 V/cm, the carriers can be ejected from the PT into the right electrode. At an electric field more than 3.0 × 10^5 V/cm, the wave packet cannot form while it moves rapidly to the right PT/metal interface. It is shown that the ejected quantity of charge is noninteger.
基金Project supported by the National Natural Science Foundation of China(Grant No.11747054)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.2018M631760)+1 种基金the Project of Hebei Educational Department,China(Grant Nos.ZD2018015 and QN2018012)the Advanced Postdoctoral Programs of Hebei Province,China(Grant No.B2017003004)
文摘Tin monoxide(SnO) is an interesting two-dimensional material because it is a rare oxide semiconductor with bipolar conductivity.However, the lower room temperature mobility limits the applications of SnO in the future.Thus, we systematically investigate the effects of different layer structures and strains on the electron–phonon coupling and phonon-limited mobility of SnO.The A2uphonon mode in the high-frequency region is the main contributor to the coupling with electrons for different layer structures.Moreover, the orbital hybridization of Sn atoms existing only in the bilayer structure changes the conduction band edge and conspicuously decreases the electron–phonon coupling, and thus the electronic transport performance of the bilayer is superior to that of other layers.In addition, the compressive strain of ε=-1.0% in the monolayer structure results in a conduction band minimum(CBM) consisting of two valleys at the Γ point and along the M–Γ line, and also leads to the intervalley electronic scattering assisted by the Eg(-1)mode.However, the electron–phonon coupling regionally transferring from high frequency A2uto low frequency Eg(-1)results in little change of mobility.
文摘Phonon-assisted tunneling (PhAT) model is applied for explication of temperature-dependent conductivity and I-V characteristics measured by various investigators for graphene nanoribbons and oxides ones. Proposed model describes well not only current dependence on temperature but also the temperature-dependent I-V data using the same set of parameters characterizing material under investigation. The values of active phonons energy and field strength for tunneling are estimated from the fit of current dependence on temperature and I-V/T data with the phonon-assisted tunneling theory.