Signatures of the Higgs mode in transport through a normal-metal–superconductor junction

Gaomin Tang,Ulrich Zülicke,Christoph Bruder,Wolfgang Belzig

doi:10.1103/physrevresearch.2.022068

Abstract

A superconductor subject to electromagnetic irradiation in the terahertz range can show amplitude oscillations of its order parameter. However, coupling this so-called Higgs mode to the charge current is notoriously difficult. We propose to achieve such a coupling in a particle-hole-asymmetric configuration using a DC-voltage-biased normal-metal--superconductor tunnel junction. Using the quasiclassical Green's function formalism, we demonstrate three characteristic signatures of the Higgs mode: (i) The AC charge current exhibits a pronounced resonant behavior and is maximal when the radiation frequency coincides with the order parameter. (ii) The AC charge current amplitude exhibits a characteristic nonmonotonic behavior with increasing voltage bias. (iii) At resonance for large voltage bias, the AC current vanishes inversely proportional to the bias. These signatures provide an electric detection scheme for the Higgs mode.

Highlights

Manipulating the superconducting (SC) state using tailored light pulses is currently receiving a great deal of attention
Using the quasiclassical Green’s function formalism, we demonstrate three characteristic signatures of the Higgs mode: (i) The AC charge current exhibits a pronounced resonant behavior and is maximal when the radiation frequency coincides with the order parameter. (ii) The AC charge current amplitude exhibits a characteristic nonmonotonic behavior with increasing voltage bias. (iii) At resonance for large voltage bias, the AC current vanishes inversely proportional to the bias
We demonstrate that the Higgs mode will manifest itself in intriguing properties of the AC charge current through the junction [see Fig. 1(c)]

Summary

Rapid Communications

Signatures of the Higgs mode in transport through a normal-metal–superconductor junction. A superconductor subject to electromagnetic irradiation in the terahertz range can show amplitude oscillations of its order parameter. Coupling this so-called Higgs mode to the charge current is notoriously difficult. (iii) At resonance for large voltage bias, the AC current vanishes inversely proportional to the bias. Using the quasiclassical Green’s function formalism, we demonstrate three characteristic signatures of the Higgs mode: (i) The AC charge current exhibits a pronounced resonant behavior and is maximal when the radiation frequency coincides with the order parameter. These signatures provide an electric detection scheme for the Higgs mode

Introduction

Published by the American Physical Society

Discussion

Conclusion