Role of Nottingham effect in the heat transfer in extreme near-field regime

TL;DR

This paper investigates heat transfer mechanisms between two metals in the extreme near-field regime, highlighting the roles of photons, phonons, and electrons, and emphasizing the Nottingham effect's influence under different bias voltages.

Contribution

It provides a detailed analysis of the relative contributions of photon, phonon, and electron tunneling to heat transfer, and explores the Nottingham effect's impact in this regime.

Findings

Electrons and phonons contribute equally near contact at low bias.

Photon contribution becomes negligible at low bias.

Electrons dominate heat transfer at higher bias voltages.

Abstract

We analyze the heat transfer between two metals separated by a vacuum gap in the extreme near-field regime. In this cross-over regime between conduction and radiation, heat exchanges are mediated by photon, phonon and electron tunneling. We quantify the relative contribution of these carriers with respect to both the separation distance between the two bodies and the applied bias voltage. In the presence of a weak bias ($V_{\rm b}<100$~mV), electrons and phonons can contribute equally to the heat transfer near contact, while the contribution of photons becomes negligible. On the other hand, for larger bias voltages, electrons play a dominant role. Moreover, we demonstrate that depending on the magnitude of this bias, electrons can either cool down or heat up the hot body by the Nottingham effect. Our results emphasize some inconsistencies in recent experimental results about heat exchanges in the extreme near-field regime and set a road map for future experiments.