title: Amplitude Higgs Mode and Admittance in Superconductors with a Moving Condensate.
abstract: We consider the amplitude (Higgs) mode in a superconductor with a condensate flow (supercurrent). We demonstrate that, in this case, the amplitude mode corresponding to oscillations δ|Δ|_{Ω}exp(iΩt) of the superconducting gap is excited by an external ac electric field E_{Ω}exp(iΩt) already in the first order in |E_{Ω}|, so that δ|Δ|_{Ω}∝(v_{0}E_{Ω}), where v_{0} is the velocity of the condensate. The frequency dependence δ|Δ|_{Ω} has a resonance shape with a maximum at Ω=2Δ. In contrast to the standard situation without the condensate flow, the oscillations of the amplitude δ|Δ(t)| contribute to the admittance Y_{Ω}. We provide a formula for admittance of a superconductor with a supercurrent. The predicted effect opens new ways of experimental investigation of the amplitude mode in superconductors and materials with superconductivity competing with other states.
authors.affiliation: Theoretische Physik III, Ruhr-Universität Bochum, D-44780 Bochum, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Moor
authors.affiliation: Theoretische Physik III, Ruhr-Universität Bochum, D-44780 Bochum, Germany.
authors.forename: Anatoly F
authors.initials: AF
authors.lastname: Volkov
authors.affiliation: Theoretische Physik III, Ruhr-Universität Bochum, D-44780 Bochum, Germany.
authors.forename: Konstantin B
authors.initials: KB
authors.lastname: Efetov