A THz time-domain susceptibility for superconductors including strong-current effects

Abstract

Finite-difference time-domain methods are increasingly being used to develop, model and analyze the response of materials, including engineered metamaterials that may contain superconductors. Though simple and useful expressions for the time-domain susceptibility exist for basic metals and dielectrics, the time-domain response for a superconductor has not been developed, mainly because the frequency-dependent expressions themselves are rather complex. In this paper we present a simple approximate expression for the time-domain susceptibility of a superconductor for the hbar/2Delta time scale (where Delta is the BCS energy gap) that fulfills causality requirements, and demonstrate its ability to model the transmission and reflection of a fully-gapped superconductor in the THz region. By allowing Delta to be a function of current, we also show how this model function can be used to describe nonlinear microwave response in superconductors.

References in corpus (5)

• The Physics and Applications of Superconducting Metamaterials
• Low Loss and Magnetic Field-tuned Superconducting THz Metamaterial
• Far-Infrared Conductivity Measurements of Pair Breaking in Superconducting Nb${}_{0.5}$Ti${}_{0.5}$N Thin Films Induced by an External Magnetic Field
• High-Q terahertz metamaterial from superconducting niobium nitride films
• Finite-Difference and Pseudospectral Time-Domain Methods Applied to Backwards-Wave Metamaterials

Cited by in corpus (3)

• Polarization-resolved terahertz third-harmonic generation in a superconductor NbN: dominance of Higgs mode beyond the BCS approximation
• Theory of coherent oscillations detection in THz pump-probe spectroscopy: from phonons to electronic collective modes
• Population inversion and dynamical phase transitions in a driven superconductor