Resonant multiple Andreev reflections in mesoscopic superconducting junctions

TL;DR

This paper studies how resonances in superconducting quantum contacts affect subharmonic gap structures, revealing enhanced odd-order features and large current peaks due to resonance effects during multiple Andreev reflections.

Contribution

It uncovers two new features of subharmonic gap structures in resonant junctions, highlighting the impact of electron resonances on Andreev reflection processes.

Findings

Enhanced odd-order structures with pronounced peaks.

Suppressed even-order structures near Fermi level.

Large current peaks at specific voltages related to resonance.

Abstract

We investigate the properties of subharmonic gap structure (SGS) in superconducting quantum contacts with normal-electron resonances. We find two distinct new features of the SGS in resonant junctions which distinguish them from non-resonant point contacts: (i) The odd-order structures on the current-voltage characteristics of resonant junctions are strongly enhanced and have pronounced peaks, while the even-order structures are suppressed, in the case of a normal electron resonance being close to the Fermi level. (ii) Tremendous current peaks develop at $eV=\pm 2E_0$ where $E_0$ indicates a distance of the resonance to the Fermi level. These properties are determined by the effect of narrowing of the resonance during multiple Andreev reflections and by overlap of electron and hole resonances.