Phase stiffness in flat-band superconductors with nodal pairing

TL;DR

This paper investigates how momentum-dependent hybridization affects the quasiparticle spectrum and phase stiffness in flat-band superconductors, revealing a quadratic temperature dependence and disorder sensitivity.

Contribution

It introduces the concept of parabolic nodes in the quasiparticle spectrum caused by interband mixing and intraband pairing in flat-band systems.

Findings

Quadratic temperature dependence of phase stiffness at low temperatures.

Presence of parabolic nodes in the quasiparticle spectrum.

Sensitivity of flat-band superconductivity to nonmagnetic disorder.

Abstract

We study Bogoliubov quasiparticle spectrum in a two-band system with momentum-dependent hybridization between a dispersive band and a flat band. The interplay between the interband mixing and intraband Cooper pairing may give rise to a parabolic node in the spectrum of flat band quasiparticles, resulting in a quadratic temperature dependence of the superconducting phase stiffness at low temperatures. We also comment that nonmagnetic disorder induces Machida-Shibata deep subgap resonances suggesting the sensitivity of flat-band superconductivity to disorder.