Microwave-Assisted Thermoelectricity in S - I - S′ Tunnel Junctions

Abstract

Asymmetric superconducting tunnel junctions with gaps ${\mathrm{\ensuremath{\Delta}}}_{1}>{\mathrm{\ensuremath{\Delta}}}_{2}$ have been proven to show a peculiar nonlinear bipolar thermoelectric effect. This arises due to the spontaneous breaking of electron-hole symmetry in the system, and it is maximized at the matching-peak bias $|V|={V}_{p}=({\mathrm{\ensuremath{\Delta}}}_{1}\ensuremath{-}{\mathrm{\ensuremath{\Delta}}}_{2})/e$. In this paper, we investigate the interplay of photon-assisted tunneling (PAT) and bipolar thermoelectric generation. In particular, we show how thermoelectricity, at the matching peak, is supported by photon absorption and emission processes at the frequency-shifted sidebands $V=\ifmmode\pm\else\textpm\fi{}{V}_{p}+n\ensuremath{\hbar}\ensuremath{\omega}$, $n\ensuremath{\in}\mathbb{Z}$. This represents a sort of microwave-assisted thermoelectricity. We show the existence of multiple stable solutions, being associated with different photon sidebands, when a load is connected to the junction. Finally, we discuss how the nonlinear cooling effects are modified by the PAT. The proposed device can detect millimeter-wavelength signals by converting a temperature gradient into a thermoelectric current or voltage.