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Thermodynamic consistency of the optomechanical master equation
摘要： We investigate the thermodynamic consistency of the master equation description of heat transport through an optomechanical system attached to two heat baths, one optical and one mechanical. We employ three different master equations to describe this scenario: (i) The standard master equation used in optomechanics, where each bath acts only on the resonator that it is physically connected to; (ii) the so-called dressed-state master equation, where the mechanical bath acts on the global system; and (iii) what we call the global master equation, where both baths are treated nonlocally and affect both the optical and mechanical subsystems. Our main contribution is to demonstrate that, under certain conditions including when the optomechanical coupling strength is weak, the second law of thermodynamics is violated by the first two of these pictures. In order to have a thermodynamically consistent description of an optomechanical system, therefore, one has to employ a global description of the effect of the baths on the system.
关键词： heat transport,thermodynamics,second law of thermodynamics,optomechanics,master equation
更新于2025-09-23 15:21:01
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Energy transport analysis in a Ga <sub/>0.84</sub> In <sub/>0.16</sub> N/GaN heterostructure using microscopic Raman images employing simultaneous coaxial irradiation of two lasers
摘要： Anisotropic heat transport in a Ga0.84In0.16N/GaN-heterostructure on a sapphire substrate is observed from microscopic Raman images obtained by utilizing coaxial irradiation of two laser beams, one for heating (325 nm) in the GaInN layer and the other for signal probing (325 nm or 532 nm). The increase in temperatures of the GaInN layer and the underlying GaN layer is probed by the 325-nm and 532-nm lasers, respectively, by analyzing the shift in the Raman peak energy of the higher energy branch of E2 modes. The result reveals that energy diffuses across a considerable length in the GaInN layer, whereas the energy transport in the perpendicular direction to the GaN layer is blocked in the vicinity of mis?t dislocations on the heterointerface. This simultaneous irradiation of two lasers for heat generation and probing is effective in the microscopic analysis of energy transport through heterointerfaces.
关键词： coaxial laser irradiation,heat transport,Raman imaging,GaInN/GaN heterostructure
更新于2025-09-23 15:19:57
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Anharmonic stabilization and lattice heat transport in rocksalt <i>β</i> -GeTe
摘要： Peierls-Boltzmann transport equation, coupled with third-order anharmonic lattice dynamics calculations, has been widely used to model lattice thermal conductivity (jl) in bulk crystals. However, its application to materials with structural phase transition at relatively high temperature is fundamentally challenged by the presence of lattice instabilities (imaginary phonon modes). Additionally, its accuracy suffers from the absence of higher-than-third-order phonon scattering processes, which are important near/above the Debye temperature. In this letter, we present an effective scheme that combines temperature-induced anharmonic phonon renormalization and four-phonon scattering to resolve these two theoretical challenges. We apply this scheme to investigate the lattice dynamics and thermal transport properties of GeTe, which undergoes a second-order ferroelectric phase transition from rhombohedral a-GeTe to rocksalt b-GeTe at about 700 K. Our results on the high-temperature phase b-GeTe at 800 K con?rm the stabilization of b-GeTe by temperature effects. We ?nd that considering only three-phonon scattering leads to signi?cantly overestimated jl of 3.8 W/mK at 800 K, whereas including four-phonon scattering reduces jl to 1.7 W/mK, a value comparable with experiments. To explore the possibility to further suppress jl, we show that alloying b-GeTe with heavy cations such as Pb and Bi can effectively reduce jl to about 1.0 W/mK, whereas particle size needs to be around 10 nm through nanostructuring to achieve a comparable reduction in jl.
关键词： rocksalt β-GeTe,lattice heat transport,thermal conductivity,phonon scattering,anharmonic stabilization
更新于2025-09-10 09:29:36