Electromagnetic Response of a Pancake Vortex in Layered Superconductors

We use the quasiclassical theory of superconductivity to calculate the response of the currents in the core of a vortex to an alternating electric field. We consider relatively clean superconductors with a mean free path, l, larger than the coherence length, ξ0. The current response of the core is dominated by the bound states of Caroli, de Gennes and Matricon, and differs significantly from the response obtained from the model of a “normal core” introduced by Bardeen and Stephen. The model of Bardeen and Stephen describes the limit of a dirty core (l ≪ ξ0), and fails for a clean superconductor. The response of the bound states includes non-dissipative acceleration of the charge carriers as well as dissipative currents. Dissipation dominates at low frequencies (h̄ω <∼ .5∆), and Reσ(ω) greatly exceeds the normal state conductivity. These dissipative currents have a dipolar structure superimposed on an oscillating supercurrent in the direction of the electric field. We attribute the anomalous dissipation to the zero-energy bound state broadened by lifetime effects. 1