Thermal conductivity of nanowires

Thermal conductivity of nanowires(NWs)is a crucial criterion to assess the operating performance of NWs-based device applications,such as in the field of heat dissipation,thermal management,and thermoelectrics.Therefore,numerous research interests have been focused on controlling and manipulating thermal conductivity of one-dimensional materials in the past decade.In this review,we summarize the state-of-the-art research status on thermal conductivity of NWs from both experimental and theoretical studies.Various NWs are included,such as Si,Ge,Bi,Ti,Cu,Ag,Bi2Te3,ZnO,AgTe,and their hybrids.First,several important size effects on thermal conductivity of NWs are discussed,such as the length,diameter,orientation,and cross-section.Then,we introduce diverse nanostructuring pathways to control the phonons and thermal transport in NWs,such as alloy,superlattices,core-shell structure,porous structure,resonant structure,and kinked structure.Distinct thermal transport behaviors and the associated underlying physical mechanisms are presented.Finally,we outline the important potential applications of NWs in the fields of thermoelectrics and thermal management,and provide an outlook.

Erratum: A Ubiquitous Thermal Conductivity Formula for Liquids, Polymer Glass, and Amorphous Solids [Chin. Phys. Lett. 37(2020) 104401]

In the Acknowledgement, the following sentence "JH and JL are supported by the National Science Foundation (Award number CBET-1943813) and the Faulty Research and Professional Development Fund at North Carolina State University" should be changed to "JH and JL are supported by the Faulty Research and Professional Development Fund at North Carolina State University".

A Ubiquitous Thermal Conductivity Formula for Liquids, Polymer Glass, and Amorphous Solids

The microscopic mechanism of thermal transport in liquids and amorphous solids has been an outstanding problem for a long time.There have been several approaches to explain the thermal conductivities in these systems,for example,Bridgman's formula for simple liquids,the concept of the minimum thermal conductivity for amorphous solids,and the thermal resistance network model for amorphous polymers.Here,we present a ubiquitous formula to calculate the thermal conductivities of liquids and amorphous solids in a unified way,and compare it with previous ones.The calculated thermal conductivities using this formula without fitting parameters are in excellent agreement with the experimental data.Our formula not only provides a detailed microscopic mechanism of heat transfer in these systems,but also resolves the discrepancies between existing formulae and experimental data.

Chiral phonon activated spin Seebeck effect in chiral materials

Efficient generation of spin polarization is very important for spintronics and quantum computation. In chiral materials without magnetic order nor spin-orbit coupling, we find a new spin selectivity effect—chiral phonon activated spin Seebeck(CPASS)effect. Starting with the nonequilibrium distribution of chiral phonons under a temperature gradient, the CPASS coefficients are computed based on the Boltzmann transport theory. With both the phonon-drag and band transport contributions, the spin accumulations generated by the CPASS effect exhibit quadratic dependence on the temperature gradient. The strength of the CPASS effect and the relative magnitude of both contributions are tunable by the chemical potential modulation. The CPASS effect, which gives a promising explanation on the traditional chiral-induced spin selectivity effect, provides opportunities for the exploration of advanced spintronic devices based on chiral materials even in the absence of any magnetic order and spin-orbit coupling.

Carbon honeycomb structure with high axial thermal transport and strong robustness

Thermal transport properties of low-dimensional nanomaterials are highly anisotropic and sensitive to the structural disorder,which can greatly limit their applications in heat dissipation.In this work,we unveil that the carbon honeycomb structures which have high in-plane thermal conductivity simultaneously possess high axial thermal conductivity.Based on non-equilibrium molecular dynamics simulations,we find that the intrinsic axial thermal conductivity of carbon honeycomb structure reaches 746 W·m^(-1)·K^(-1)at room temperature,comparable to that of good heat dissipation materials such as hexagonal boron nitride.By comparing the phonon transmission spectrum between carbon honeycombs and few layer graphene,the physical mechanism responsible for the high axial thermal conductivity of carbon honeycombs is discussed.More importantly,our simulation results further demonstrate that the high axial thermal conductivity of carbon honeycomb structure is robust to the structural disorder,which is a common issue during the mass production of the carbon honeycomb structure.Our study suggests that the carbon honeycomb structure has unique advantages to serve as the thermal management material for practical applications.

Emerging theory and phenomena in thermal conduction: A selective review

Recently, emerging phonon phenomena have been discovered and rapidly developed, which have become an active hot research topic. In this review article, we present state-of-the-art advances in several fascinating phonon transport phenomena. First, we summarize the recent progress on the wave nature of phonons, including phonon coherence and its effects on thermal conductivity and the topological properties of phonons. Then, we discuss the particle nature of phonons, including the weak coupling of phonons and the high-order phonon anharmonicity. Finally, we present the summary and a brief outlook. This review presents the advanced understanding of some emerging phonon phenomena in solid materials, which provides new opportunities for further advancement in a wide variety of applications.

How coherence is governing diffuson heat transfer in amorphous solids

Thermal transport in amorphous materials has remained one of the fundamental questions in solid state physics while involving a very large field of applications.Using a heat conduction theory incorporating coherence,we demonstrate that the strong phase correlation between local and non-propagating modes,commonly named diffusons in the terminology of amorphous systems,triggers the conduction of heat.By treating the thermal vibrations as collective excitations,the significant contribution of diffusons,predominantly relying on coherence,further reveals interesting temperature and length dependences of thermal conductivity.The propagation length of diffuson clusters is found to reach the micron,overpassing the one of propagons.The explored wavelike behavior of diffusons uncovers the unsolved physical picture of mode correlation in prevailing models and further provides an interpretation of their ability to transport heat.This work introduces a framework for understanding thermal vibrations and transport in amorphous materials,as well as an unexpected insight into the wave nature of thermal vibrations.