Gapful electrons in a vortex core in granular superconductors

Abstract

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 $\xi$ becomes comparable to the distance between neighboring grains $l$. Minigap magnitude $E_g$ grows from zero at $\xi \approx 1.4l$ to third of superconducting gap ${\Delta }_0$ at $\xi \approx 0.5l$. 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.

References in corpus (3)

• Electrodynamics of granular aluminum from superconductor to insulator: observation of collective superconducting modes
• Superconducting phases and the second Josephson harmonic in tunnel junctions between diffusive superconductors
• Vortex core near planar defects in a clean layered superconductor

Cited by in corpus (2)

• Quantum Coherence in Superconducting Vortex States
• Vortex Pinning in Niobium covered by a thin polycrystalline Gold