# Heat rectification, heat fluxes, and spectral matching

## TL;DR

This paper analytically investigates heat rectification in a minimal ion chain, establishing a theoretical relation between spectral matching and heat flux, and providing insights for designing efficient thermal devices.

## Contribution

It derives an explicit, first-principles relation between spectral matching and heat flux in a minimal ion chain model, advancing understanding of heat rectification mechanisms.

## Key findings

- Analytical expressions for heat fluxes and rectification in a two-ion chain.
- Proposed a spectral matching measure that bounds heat flux.
- Found proportionality between matching and flux ratios at optimal rectification.

## Abstract

Heat rectifiers would facilitate energy management operations such as cooling, or energy harvesting, but devices of practical interest are still missing. Understanding heat rectification at a fundamental level is key to help us find or design such devices. The match or mismatch of the phonon band spectrum of device segments for forward or reverse temperature bias of the thermal baths at device boundaries, was proposed as the mechanism behind rectification. However no explicit, theoretical relation derived from first principles had been found so far between heat fluxes and spectral matching. We study heat rectification in a minimalistic chain of two coupled ions. The fluxes and rectification can be calculated analytically. We propose a definition of the matching that sets an upper bound for the heat flux. In a regime where the device rectifies optimally, matching and flux ratios for forward and reverse configurations are found to be proportional. The results can be extended to a system of N particles in arbitrary traps with nearest-neighbor linear interactions.