Higgs amplitude mode in ballistic superconducting hybrid junctions

TL;DR

This paper proposes a novel method to detect the Higgs amplitude mode in superconductors through electronic transport measurements in ballistic hybrid devices, revealing resonant and gap features linked to the mode.

Contribution

It introduces a new approach to probe the Higgs mode using transport in hybrid superconducting devices, confirmed via theoretical modeling.

Findings

Higgs mode appears in the second-order AC current in NIS junctions.

DC conductance in NSN junctions reveals Higgs-induced gaps.

Theoretical confirmation of Higgs mode existence in clean superconductors.

Abstract

In superconductors (SC), the Higgs amplitude mode is a coherent oscillation of the order parameter typically generated by THz laser irradiation. In this paper we propose to probe the Higgs mode using electronic transport in ballistic superconducting hybrid devices. We first confirm the existence of a non-zero amplitude mode in the clean case using the Keldysh-Eilenberger formalism. We then investigate two different geometries, respectively a normal-insulating-superconductor (NIS) tunnel junction and a NSN junction with transparent interfaces, the superconductor being irradiated in both situations. In the NIS case, the Higgs manifests itself in the second-order AC current response which is resonant at the Higgs frequency. In the NSN case, the DC differential conductance allows to probe the gaps generated by the Higgs mode in the Floquet spectrum.