Effect of temperature-induced dielectric response on radiative heat transfer in the extreme near-field regime
Phys. Rev. B 114, 185425 – Published 22 September, 2026
DOI: https://doi.org/10.1103/ld38-1n1w
Abstract
We investigate radiative heat transfer in the extreme near-field regime using a microscopic approach based on the nonequilibrium Green's function (NEGF) formalism combined with first-principles simulations of the frequency- and wave-vector-dependent dielectric function. Unlike previous studies, our first-principles simulations of the dielectric function, which determines the transmission function within the NEGF framework, are performed at the actual temperature of the media. Finite temperature effects such as phonon excitations, all-order phonon scattering, and phonon anharmonicity, which are neglected in ground-state (0 K) treatments, are directly included in our first-principles approach. Electron-phonon coupling is also incorporated indirectly within the adiabatic approximation through thermally displaced atomic configurations. Using two graphene sheets as a model system, we show that ground-state dielectric function fails to reproduce the response of the material, particularly at high temperatures and low frequencies where phonons are excited. The phonon anharmonicity increases both the real and imaginary parts of the dielectric function at low frequencies. Our simulations demonstrate that when ground-state dielectric function is used for predicting radiative conductance, an error in the range of 32–43% is obtained for a temperature of 1200 K depending on the gap size. The anharmonic effects on radiative conductance are strongest at medium temperatures and neglecting these effects results in 8.4–25.6% underestimation of the radiative conductance at 750 K. Last, we find that the gap dependence of the conductance follows a power-law behavior of , where varies slightly from 1.39 to 1.48 depending on the temperature. Our work establishes a first-principles framework that incorporates finite-temperature and anharmonic effects into microscopic theories of extreme near-field thermal radiation and demonstrates that these effects are essential for accurate modeling of radiative heat transfer in this regime.
