# Thermal rectification and negative differential thermal conductance in harmonic chains with nonlinear system-bath coupling

## TL;DR

This paper demonstrates thermal rectification and negative differential thermal conductance in harmonic chains by incorporating nonlinear system-bath coupling, revealing how coupling strength influences heat transport and rectification direction.

## Contribution

It introduces a generalized Caldeira-Leggett model with nonlinear system-bath coupling, extending previous linear models to explain thermal phenomena in harmonic chains.

## Key findings

- Weak linear coupling enhances heat current via multiphonon processes.
- Asymmetric nonlinear coupling induces thermal rectification.
- Strong linear coupling suppresses heat current and reverses rectification direction.

## Abstract

Thermal rectification and negative differential thermal conductance were realized in harmonic chains in this work. We used the generalized Caldeira-Leggett model to study the heat flow. In contrast to the most previous studies considering only the linear system-bath coupling, we considered the nonlinear system-bath coupling based on recent experiment [A. Eichler \emph{et al.}, Nat. Nanotech. \textbf{6}, 339 (2011)]. When the linear coupling constant is weak, the multiphonon processes induced by the nonlinear coupling allow more phonons transport across the system-bath interface and hence the heat current is enhanced. Consequently, thermal rectification and negative differential thermal conductance are achieved when the nonlinear couplings are asymmetric. However, when the linear coupling constant is strong, the umklapp processes dominate the multiphonon processes. Nonlinear coupling suppresses the heat current. Thermal rectification is also achieved. But the direction of rectification is reversed comparing to the results of weak linear coupling constant.