Giant Thermoelectric Response of Fluxons in Superconductors

We investigate the thermoelectric response of an Abrikosov vortex in type-II superconductors in the deep quantum limit. We consider two thermoelectric geometries, a type-II superconductor-insulator-normal-metal (S-I-N) junction and a local scanning tunneling microscope (STM)-tip normal metal probe over the superconductor. We exploit the strong breaking of particle-hole symmetry in vortex-bound states at subgap energies within the superconducting vortex to realize a giant thermoelectric response in the presence of fluxons. We predict a thermovoltage of a few mV/K at subkelvin temperatures using both semianalytic and numerical self-consistent solutions of the Bogoliubov-de Gennes equations. Relevant thermoelectric coefficients and figures of merit ZT are found within our models, both in linear and nonlinear regimes. ZT of the S-I-N junction is around 1, rising to above 3 for the STM junction centered at the vortex core. We also discuss how this system can be used as a sensitive low-temperature thermocouple, or a localized bolometer to detect low-energy single photons.