Magnetic-field-induced transition in a quantum dot coupled to a superconductor

Abstract

The magnetic moment of a quantum dot can be screened by its coupling to a superconducting reservoir, depending on the hierarchy of the superconducting gap and the relevant Kondo scale. This screening-unscreening transition can be driven by electrostatic gating, tunnel coupling, and, as we demonstrate here, magnetic field. We perform high-resolution spectroscopy of subgap excitations near the screening-unscreening transition of asymmetric superconductor -quantum dotsuperconductor (S-QD-S) junctions formed by the electromigration technique. Our measurements reveal a re-entrant phase boundary determined by the competition between Zeeman energy and gap reduction with magnetic field. We further track the evolution of the phase transition with increasing temperature, which is also evidenced by thermal replicas of subgap states. arXiv:1912.04084v1 [cond-mat.mes-hall]

Magnetic field effect on trivial and topological bound states of superconducting quantum dot

“…In contrast to such behavior, the magnetic field applied either to N-QD-SC or S-QD-S junctions affects the quasiparticle energies of the bound states [58]. Under specific conditions they can cross each other, giving rise to enhancement of the zero-bias conductance.…”

Proposal for Detection of the 0′ and π′ Phases in Quantum-Dot Josephson Junctions

“…So, to achieve a wider region of the intermediate phases in the parameter space, the coupling in QDJJs should be more symmetric. The QDJJs in many experiments used to be highly asymmetric [38], which, we guess, is the reason why the intermediate phases have not been detected so far.…”