Quantum oscillations in the vortex state of multu-band superconductors

TL;DR

This paper explains low-frequency quantum oscillations in the vortex state of multiband superconductors as arising from the topology of Fermi surfaces and the interplay of gaps on multiple bands, linking experimental observations to band structure features.

Contribution

It introduces a theoretical framework connecting quantum oscillations in multiband superconductors to Fermi surface topology and pairing symmetry effects.

Findings

Quantum oscillations originate from small Fermi surface pockets.

Unconventional pairing symmetry affects the induced gap size.

Small Fermi surface pockets are tied to the topology of the band structure.

Abstract

We argue that the low- frequency quantum oscillations observed recently in the vortex state of underdoped ortho II-YBCO have the same origin as in other strongly correlated electronic systems. Superconductivity driven by strong interactions on several Fermi surfaces creates proximity gaps on the other. The gap transferred on a small-sized pocket from larger Fermi surfaces is small. In case of unconventional pairing symmetry the induced gap is proportional to ratio of the oscillations' frequencies for small and large Fermi surfaces. The gap is in inverse proportion to mass enhancement on the latter. We share the view that small pockets themselves are certain feature of topology of the band Fermi surfaces.