Phononic heat transport in molecular junctions: quantum effects and vibrational mismatch

TL;DR

This paper applies a quantum self-consistent reservoir method to study phononic heat transport in molecular junctions, highlighting quantum effects and vibrational mismatch impacts on thermal conductance.

Contribution

It introduces and validates a quantum simulation approach for phononic heat transfer in molecular junctions under far-from-equilibrium conditions.

Findings

Thermal conductance behavior matches expected anharmonic chain models.

Vibrational mismatch influences heat transfer via phonon recombination.

Anharmonicity increases resistance but can facilitate energy transfer.

Abstract

Problems of heat transport are ubiquitous to various technologies such as power generation, cooling, electronics, and thermoelectrics. In this paper we advocate for the application of the quantum self-consistent reservoir method, which is based on the generalized quantum Langevin equation, to study phononic thermal conduction in molecular junctions. The method emulates phonon-phonon scattering processes while taking into account quantum effects and far-from-equilibrium (large temperature difference) conditions. We test the applicability of the method by simulating the thermal conductance of molecular junctions with one-dimensional molecules sandwiched between solid surfaces. Our results satisfy the expected behavior of the thermal conductance in anharmonic chains as a function of length, phonon scattering rate and temperature, thus validating the computational scheme. Moreover, we examine the effects of vibrational mismatch between the solids' phonon spectra on the heat transfer characteristics in molecular junctions. Here, we reveal the dual role of vibrational anharmonicity: It raises the resistance of the junction due to multiple scattering processes, yet it promotes energy transport across a vibrational mismatch by enabling phonon recombination and decay processes.