Nonlocal thermoelectric engines in hybrid topological Josephson junctions

TL;DR

This paper investigates the thermoelectric performance of a topological Josephson nonlocal heat engine, revealing high nonlocal Seebeck coefficients and analyzing effects of flux, phase bias, and nonidealities on efficiency and power.

Contribution

It introduces a detailed analysis of nonlocal thermoelectric effects in topological Josephson junctions, including experimental considerations and optimization of power and efficiency.

Findings

High nonlocal Seebeck coefficient (~0.1 μV/K at a few kelvin)

Nonlocal response is robust against moderate gap asymmetries

Maximum power coincides with maximum efficiency in optimal conditions

Abstract

The thermoelectric performance of a topological Josephson nonlocal heat engine is thoroughly investigated. The nonlocal response is obtained by using a normal metal probe coupled with only one of the proximized helical edges in the middle of the junction. In this configuration, we investigate how the flux bias and the phase bias trigger the nonlocal thermoelectric effects under the application of a thermal difference between the superconducting terminals. Possible experimental nonidealities such as asymmetric proximized superconducting gaps are considered showing how the nonlocal response can be affected. The interplay between Doppler-shift, which tends to close gaps, and Andreev interferometry, which affects particle-hole resonant transport, are clearly identified for different operating regimes. Finally, we discuss the power and the efficiency of the topological thermoelectric engine which reaches maximum power at maximal efficiency for a well coupled normal probe. We find quite high nonlocal Seebeck coefficient of the order of tenths of $\mu$V/K at a few kelvin, a signal that would be clearly detectable also against any spurious local effect even with moderate asymmetry of the gaps.