Steady-state heat current through harmonically and bilinearly coupled asymmetric leads

Abstract

We study heat transport through a junction of two harmonic leads coupled together by a spring via a bilinear or harmonic coupling using the nonequilibrium Green's function formalism. For harmonically coupled leads, we find that the optimal current occurs when the two leads have matching energy spectra. However, at low temperatures, the maximal heat current may not coincide with spectral matching because the higher frequency modes do not contribute to the heat current. On the other hand, the optimal heat current always occurs  under asymmetric conditions in the bilinear approximation. We also find that the transmission function due to the bilinear coupling may exclude the high frequency modes even at high temperatures.