title: Reduction of dissipative nonlinear conductivity of superconductors by static and microwave magnetic fields.
abstract: A theory of dissipative nonlinear conductivity, σ(1)(ω,H), of s-wave superconductors under strong electromagnetic fields at low temperatures is proposed. Closed-form expressions for σ(1)(H) and the surface resistance R(s)(ω,H) are obtained in the nonequilibrium dirty limit for which σ(1)(H) has a significant minimum as a function of a low-frequency (ħω ≪ k(B)T) magnetic field H. The calculated microwave suppression of R(s)(H) is in good agreement with recent experiments on alloyed Nb resonator cavities. It is shown that superimposed dc and ac fields, H = H(0) + H(a)cosωt, can be used to reduce ac dissipation in thin film nanostructures by tuning σ(1)(H(0)) with the dc field.
authors.affiliation: Department of Physics and Center for Accelerator Science, Old Dominion University, 4600 Elkhorn Avenue, Norfolk, Virginia 23529, USA.
authors.forename: A
authors.initials: A
authors.lastname: Gurevich