Giant microwave absorption in the vortex lattice in $s$-wave superconductors

TL;DR

This paper reveals a new dominant microwave absorption mechanism in s-wave superconductors with vortex lattices, caused by quasiparticle density fluctuations outside vortex cores, affecting conductivity across frequency ranges.

Contribution

It introduces a novel absorption mechanism independent of vortex motion, highlighting the role of quasiparticle density dynamics in microwave response.

Findings

New absorption mechanism dominates in broad parameter ranges

Low-frequency conductivity linked to inelastic relaxation time

High-frequency conductivity related to quasiparticle diffusion time

Abstract

In this article we study microwave absorption in superconductors in the presence of a vortex lattice. We show that in addition to the conventional absorption mechanism associated with the vortex core motion, there is another mechanism of microwave absorption, which is caused by the time-dependence of the quasiparticle density of states outside the vortex cores. This mechanism exists even in the absence of vortex motion and provides the dominant contribution to microwave absorption in a broad interval of physical parameters. At low frequencies, the dissipative part of the microwave conductivity $\sigma(\omega)$ is proportional to the inelastic relaxation time, $\tau_{\mathrm{in}}$, which is typically much larger than the elastic relaxation time, $\tau_{\mathrm{el}}$. At high frequencies $\sigma(\omega)$ is proportional to the quasiparticle diffusion time across the inter-vortex distance, $\tau_{\mathrm D}$, which is still larger than $\tau_{\mathrm{el}}$.