Supercurrent induced resonant optical response

Abstract

The optical conductivity encodes the current response to a time dependent electric field. We develop a theory of the optical conductivity $\sigma (\omega )$ in presence of a dc supercurrent. Current induced optical response is prohibited by Galilean invariance from occurring in systems with a single parabolic band. However, we show that lattice effects give rise to a pronounced current dependent peak in $\sigma (\omega )$ at the gap edge $\omega =2\Delta$, which diverges in the clean limit. We demonstrate this in a model of a multi-band superconductor. Our theory explains the recent observation of a current induced peak in the optical conductivity in NbN by Nakamura et al. (2019), and provides a new mechanism for direct activation of the Higgs mode with light.

12 pages, 5 figures

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• Chirped amplitude mode in photo-excited superconductors
• Long-lived Higgs modes in strongly correlated condensates
• Proposal for Superconducting Photodiode
• Supercurrent-induced Anomalous Thermal Hall Effect as a New Probe to Superconducting Gap Anisotropy
• Reducing the frequency of the Higgs mode in a helical superconductor coupled to an LC-circuit
• Vertex correction for the linear and nonlinear optical responses in superconductors: multiband effect and topological superconductivity
• Nonreciprocal Nonlinear Responses in Moving Charge Density Waves
• Optical absorption activated by an ultrashort half-cycle pulse in metallic and superconducting states of the Hubbard model
• Optical conductivity of a dirty current-carrying superconductor
• Supercurrent effect in a charge density wave intertwined superconductor
• Vertex corrections to nonlinear photoinduced currents in 2D superconductors