Classification and characterization of nonequilibrium Higgs modes in unconventional superconductors

TL;DR

This paper develops a theoretical framework to classify and characterize nonequilibrium Higgs modes in unconventional superconductors, linking oscillation symmetries to ground state gap symmetries through group theory and simulations.

Contribution

It introduces a comprehensive classification scheme for Higgs oscillations based on lattice symmetry and quench conditions, supported by analytic and numerical analysis.

Findings

Higgs oscillations serve as fingerprints for gap symmetry

Finite momentum transfer influences Higgs mode identification

Simulations match theoretical predictions for optical responses

Abstract

Recent findings of new Higgs modes in unconventional superconductors require a classification and characterization of the modes allowed by nontrivial gap symmetry. Here we develop a theory for a tailored nonequilibrium quantum quench to excite all possible oscillation symmetries of a superconducting condensate. We show that both a finite momentum transfer and quench symmetry allow for an identification of the resulting Higgs oscillations. These serve as a fingerprint for the ground state gap symmetry. We provide a classification scheme of these oscillations and the quench symmetry based on group theory for the underlying lattice point group. For characterization, analytic calculations as well as full scale numeric simulations of the transient optical response resulting from an excitation by a realistic laser pulse are performed. Our classification of Higgs oscillations allows us to distinguish between different symmetries of the superconducting condensate.