Thermoelectric Transport Properties Of Multiple Weyl Semimetals At The Quantum Limit

In the field of condensed matter physics,the study of transport properties of topological materials is very interesting and important research topics.Since the topological insulator was first discovered,people have been devoted to finding more topological materials and classifying them.Topological materials can be classified into topological insulators and topological semimetals by using topological invariants.Using topological invariants we can divide materials into topological insulators and topological semimetals.In 1929 Weyl discovered that when the mass term is zero,the Dirac equation can be separated into two Weyl equations,and this material is called Weyl semimetal.Weyl semimetals are topological semimetals that support Weyl fermions as low energy excitation.The monopole in momentum space has opposite topological charge and no gap spectrum.The integer monopole appears in pairs and acts as the source or sink of Berry curvature.These monopole form Weyl points,which are the contact points between conduction band and valence band.Transport is one of the most important characteristics of topological materials,which is very important for the development of thermoelectric materials and low power loss.Due to its unique electronic structure and physical properties,people are interested in the thermoelectric properties of topologically nontrival band structures.The contribution of electrons to the thermoelectric response coefficient reflects the properties of quasiparticle dispersion and in this way,it provides a method to study the properties of electron.Thermoelectric materials can realize the conversion between heat energy and electric energy.The research on their thermoelectric properties has been paid much attention.In recent years,thermoelectric research has been transferred to topological semimetals.In the early stage of the development of thermoelectric materials,metal materials were studied,and thermoelectric conversion efficiency was very low.With the energy band theory being put forward,thermoelectric materials have been further developed with the advent of semiconductor materials.So far,semiconductor with narrow band gap has been found to be a better thermoelectric material.Subsequently,linear dispersion relationships,fermi arcs,chiral anomalies and ultra-high carrier mobility of topological semimetals have attracted people to the thermoelectric transport properties of topological materials.It is found that topological semimetals can improve the thermoelectric transport coefficient.In this paper,we mainly study the thermoelectric transport properties of multiple Weyl semimetals.Multi-Weyl semimetals are a new type of topological semimetals with magnetic monopole greater than 1,linear dispersion along the symmetric direction,and nonlinear dispersion relationship in two transverse directions.We use linear response theory to study the transport properties and thermoelectric response of topological materials.We use Gaussian and screened Coulomb electron-impurity scatterings with different scattering ranges.Under the action of an applied electric and magnetic field.When the magnetic field is parallel to the electric field or temperature gradient,we find that the resistivity decreases with the increase of the magnetic field,presenting the phenomenon of negative resistivity,the thermoelectric potential depends strongly on the type of scattering potential and monopole.When the magnetic fields and electric fields or temperature gradients are perpendicular to each other,the thermoelectric transport becomes complicated,we find that at low electron density,the magnitude of the longitudinal conductivity becomes comparable to the Hall conductivity with the increase of magnetic field.In this process,the Seebeck and Neneste response coefficients do not increase continuously,especially for large monopole.However,under d = 6nm Gaussian impurity scattering potential,Seebeck and Nenst coefficients still continue to increase and appear unsaturated phenomenon.When d < 6nm,the behavior of non-continuous growth occurs.We demonstrate that thermoelectric Hall conductivity still shows a platform feature.Whether the longitudinal thermal conductivity increases with the increase of field is affected by the type of scattering potential.The variation of thermoelectric Hall conductance is different at different scattering potentials.From this phenomenon,we can reveal the scattering mechanism of multiple Weyl semimetals...