Large thermoelectric power and figure of merit in a ferromagnetic-quantum dot-superconducting device

TL;DR

This study explores a ferromagnetic-quantum dot-superconducting device that exhibits high thermoelectric efficiency and tunable spin-dependent effects, driven by magnetic fields and gate voltages, with potential for spin caloritronics applications.

Contribution

It demonstrates large thermopower and figure of merit in a quantum dot device with ferromagnetic and superconducting contacts, highlighting tunability and spin control via temperature gradients.

Findings

High thermopower and figure of merit achieved.

Thermopower can be tuned with gate voltage.

Significant control of spin currents with temperature gradients.

Abstract

We investigate the thermoelectric properties of a quantum dot coupled to ferromagnetic and superconducting electrodes. The combination of spin polarized tunneling at the ferromagnetic-quantum dot interface and the application of an external magnetic field that Zeeman splits the dot energy level leads to large values of the thermopower (Seebeck coefficient). Importantly, the thermopower can be tuned with an external gate voltage connected to the dot. We compute the figure of merit that measures the efficiency of thermoelectric conversion and find that it attains high values. We discuss the different contributions from Andreev reflection processes and quasiparticle tunneling into and out of the superconducting contact. Furthermore, we obtain dramatic variations of both the magnetothermopower and the spin Seebeck effect, which suggest that in our device spin currents can be controlled with temperature gradients only.