The Berry dipole photovoltaic demon and the thermodynamics of photo-current generation within the optical gap of metals

TL;DR

This paper clarifies the thermodynamics of photo-current generation in metals, showing that Berry curvature effects can enable nearly reversible, dissipationless photovoltaic operation within the optical gap, with potential for high-efficiency infrared light amplification.

Contribution

It demonstrates that Berry curvature-induced effects can act as a reversible photovoltaic mechanism within the optical gap, challenging previous assumptions about irreversibility and dissipation.

Findings

In-gap rectification mechanisms are generally irreversible and involve energy exchange with a heat bath.

Berry curvature effects can enable reversible, dissipationless photo-current generation.

Potential for near-100% efficiency in circularly polarized light amplification.

Abstract

We dismantle the previously held misconception that it is impossible for bulk rectification mechanisms to induce a net DC electric current when the frequency of the impinging radiation lies within the optical gap of a metal in the limit of small carrier relaxation rates. We argue that generically such in-gap rectification mechanisms are irreversible and accompanied by a continuous exchange of energy with a heat bath and must also be necessarily accompanied by a small but finite absorption of radiation in order to guarantee the positivity of the net entropy production and abide by the second law of thermodynamics. We show, however, that the intra-band non-linear Hall effect arising from the Berry curvature is a special kind of in-gap rectification mechanism that behaves as a ``photo-voltaic demon'', namely it can operate as an ideal reversible and dissipationless conveyor of energy between the radiation and an external circuit. Its reversible nature allows for an interesting mode of operation as an amplifier of circularly polarized light, whose efficiency can approach 100%, and which could be technologically promising especially in the infrared frequency range.