Heat transport in an anharmonic crystal

TL;DR

This study investigates heat transport in a three-dimensional anharmonic crystal slab with baths attached to all surfaces, revealing that Fourier's law holds at leading order and the temperature profile decays exponentially.

Contribution

It demonstrates that in an anharmonic crystal, heat conduction follows Fourier's law at leading order and the temperature profile is exponentially decreasing, with thermal conductivity independent of environmental temperature.

Findings

Heat radiated does not receive correction at leading anharmonic order.

The slab's temperature profile decays exponentially.

Thermal conductivity depends only on surface temperature difference.

Abstract

We take an ordered, anharmonic crystal in the form of slab geometry in three dimensions. Apart from attaching baths of Langevin type to the extreme surfaces, we also attach baths of same type to the intermediate surfaces of the slab to simulate the environment surrounding the system. We assume noise functions to be Gaussian and their widths to be site dependent. We find that the radiated heat from the slab does not receive any correction at the leading order of anharmonic coupling and the Newton's law of cooling holds for an appropriate choice of the widths. We observe that in the steady state limit entire slab becomes an assembly of $N$ different thermally equilibriated layers, where $N$ is the number of sites in the direction of conduction current flow. We find an exponentially falling nature of the temperature profile as its leading behaviour and its non-leading behaviour is governed by the two site dependent functions. Our evaluation suggests that in the thermodynamic limit thermal conductivity remains independent of the environment temperature and is dependent only on the difference of temperature of the extreme surfaces linearly at the leading order of anharmonic coupling. We find that owing to finiteness of conductivity in the thermodynamic limit, Fourier's law holds to leading order in anharmonic coupling.