Photo-caloritronics in the THz regime: Photon-assisted thermopower generators

TL;DR

This paper investigates photon-assisted thermopower generation in a THz-driven miniaturized device, revealing how periodic driving enhances charge flow and can be controlled via amplitude and frequency, with implications for thermoelectric applications.

Contribution

It introduces a Floquet-theory-based model to analyze thermopower in a THz-driven system, demonstrating increased charge flow due to periodic perturbation and control over thermally-pumped currents.

Findings

Periodic driving increases charge flow in thermopower generation.

The thermally-pumped current can be tuned by adjusting amplitude and frequency.

Materials with linear dispersion yield larger currents due to higher density of modes.

Abstract

The generation of thermopower in a miniaturized device modeled as a channel connected to reservoirs/contacts maintained at different temperatures is studied in this work. The left reservoir is also coupled to a periodic THz driving source leading to a rearrangement of its internal energy levels. The modified levels are determined using Floquet theory that governs the dynamics of a periodic Hamiltonian. The starting point for the presented thermopower calculations (mirrored in the related thermal gradient controlled current) is the Landauer formula rooted in the transmission formalism. Primarily, we show that while thermally activated electrons can be pumped from the hot reservoir into the cold side as a straightforward manifestation of the Seebeck effect through a difference in their respective Fermi levels, the quantum of charge flow increases in presence of the periodic perturbation. We explain this phenomenon by noting how the periodic driving makes available a greater number of states in the left reservoir that are able to inject electrons into the channel. The calculations also uncover a useful feature whereby the strength of such a thermally-pumped current is amenable through a joint control of the amplitude and frequency of the signal, offering an additional experimentally-adjustable tool to regulate their flow. The calculated results are shown for two classes of materials defined by prototypical linear and quadratic dispersion, with the former capable of furnishing a larger current by virtue of higher available density-of-modes. We close by pointing out possible improvements to the calculation by accounting for dissipative effects in the channel.