- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Photoinduced tunable anomalous Hall and Nernst effects in tilted Weyl semimetals using Floquet theory
摘要： In this paper, we discuss the effect of a periodically driving circularly polarized laser beam in the high-frequency limit, on the band structure and thermal transport properties of type-I and type-II Weyl semimetals (WSMs). We develop the notion of an effective Fermi surface stemming from the time-averaged Floquet Hamiltonian and discuss its effects on the steady-state occupation numbers of electrons and holes in the linearized model. In order to compute the transport coef?cients averaged over a period of the incident laser source, we employ the Kubo formalism for Floquet states and show that the Kubo formula for the conductivity tensor retains its well-known form with the difference that the eigenstates and energies are replaced by the Floquet states and their quasienergies. We ?nd that for type-I WSMs the anomalous thermal Hall conductivity grows quadratically with the amplitude A0 of the U(1) gauge ?eld for low tilt, while the Nernst conductivity remains unaffected. For type-II WSMs, the Hall conductivity decreases nonlinearly with A0 due to the contribution from the physical momentum cutoff, required to keep ?nite electron and hole pocket sizes, and the Nernst conductivity falls off logarithmically with A2 0. These results may serve as a diagnostic for material characterization and transport parameter tunability in WSMs, which are currently the subject of a wide range of experiments.
关键词： Nernst effect,Floquet theory,anomalous Hall effect,thermal transport,Weyl semimetals
更新于2025-09-23 15:21:01
-
Effects of interfaces and current spreading on the thermal transport of micro-LEDs for kA-per-square-cm current injection levels
摘要： The three-dimensional thermal characteristics of micro-light-emitting diodes (mLEDs) on GaN and sapphire substrates were studied with forward-voltage methods, thermal transient measurements, and infrared imaging. The mLEDs on the GaN substrate showed an approximately 10 °C lower junction temperature and smaller amplitude of the K factors than those on the sapphire substrate under the current injection level of 4 kA cm?2. The thermal transient measurement showed that the spreading thermal resistances of the mesa, the GaN epilayer, and the interface of the GaN/substrate were reduced significantly for mLEDs on the GaN substrate because of the high-quality GaN crystal and the interfaces. The infrared thermal images showed lower total average junction temperatures and more uniform temperature distributions for the mLEDs on the GaN substrate, which were also simulated with APSYS software. The thermal transport mechanisms are discussed for the lateral and vertical directions in the mLEDs.
关键词： sapphire substrate,micro-light-emitting diodes,GaN substrate,junction temperature,thermal transport,infrared imaging,APSYS simulation
更新于2025-09-11 14:15:04
-
Dislocation-induced thermal transport anisotropy in single-crystal group-III nitride films
摘要： Dislocations, one-dimensional lattice imperfections, are common to technologically important materials such as III–V semiconductors, and adversely affect heat dissipation in, for example, nitride-based high-power electronic devices. For decades, conventional nonlinear elasticity models have predicted that this thermal resistance is only appreciable when the heat flux is perpendicular to the dislocations. However, this dislocation-induced anisotropic thermal transport has yet to be seen experimentally. Using time-domain thermoreflectance, we measure strong thermal transport anisotropy governed by highly oriented threading dislocation arrays throughout micrometre-thick, single-crystal indium nitride films. We find that the cross-plane thermal conductivity is almost tenfold higher than the in-plane thermal conductivity at 80?K when the dislocation density is ~3?×?1010?cm?2. This large anisotropy is not predicted by conventional models. With enhanced understanding of dislocation–phonon interactions, our results may allow the tailoring of anisotropic thermal transport with line defects, and could facilitate methods for directed heat dissipation in the thermal management of diverse device applications.
关键词： dislocations,time-domain thermoreflectance,thermal transport,anisotropy,group-III nitride films
更新于2025-09-09 09:28:46