We calculate the quasiparticle density of states (DoS) inside the vortex core in a granular superconductor, generalizing the classical solution applicable for dirty superconductors. A discrete version of the Usadel equation for a vortex is derived and solved numerically for a broad range of parameters. Electron DoS is found to be gapful when the vortex size ξ becomes comparable to the distance between neighboring grains l. Minigap magnitude Eg grows from zero at ξ≈1.4l to third of superconducting gap Δ0 at ξ≈0.5l. The absence of low-energy excitations is the main ingredient needed to understand strong suppression of microwave dissipation recently observed in a mixed state of granular Al.
@article{arxiv.2212.01862,
title = {Gapful electrons in a vortex core in granular superconductors},
author = {Dmitry E. Kiselov and Mikhail A. Skvortsov and Mikhail V. Feigel'man},
journal= {arXiv preprint arXiv:2212.01862},
year = {2023}
}