Phase-resolved Higgs response in superconducting cuprates

TL;DR

This study uses phase-resolved terahertz third harmonic generation to investigate the Higgs amplitude mode in cuprate superconductors, revealing universal phase behavior and possible pairing above the critical temperature.

Contribution

It provides the first phase-resolved measurements of the Higgs mode in cuprates, showing universal phase jumps and evidence of pairing correlations above Tc.

Findings

Universal phase jump in Higgs oscillation

Detection of non-vanishing third harmonic above Tc

Coupling of Higgs mode to other collective excitations

Abstract

In high energy physics, the Higgs field couples to gauge bosons and fermions and gives mass to their elementary excitations. Experimentally, such couplings can be inferred from the decay product of the Higgs boson, i.e. the scalar (amplitude) excitation of the Higgs field. In superconductors, Cooper pairs bear a close analogy to the Higgs field. Interaction between the Cooper pairs and other degrees of freedom provides dissipation channel for the amplitude mode, which may reveal important information about the microscopic pairing mechanism. To this end, we investigate the Higgs (amplitude) mode of several cuprate thin films using phase-resolved terahertz third harmonic generation (THG). In addition to the heavily damped Higgs mode itself, we observe a universal jump in the phase of the driven Higgs oscillation as well as a non-vanishing THG above Tc. These findings indicate coupling of the Higgs mode to other collective modes and potentially a nonzero pairing amplitude above Tc.