Gapless Fermi Surfaces in anisotropic multiband superconductors in magnetic field

TL;DR

This paper predicts a novel gapless Fermi surface state in quasi-2D multiband superconductors under in-plane magnetic fields, characterized by a paramagnetic moment and distinct thermodynamic properties.

Contribution

It introduces a new gapless state in multiband superconductors with detailed calculations and discusses experimental detection methods.

Findings

Identification of a fully gapless Fermi surface state in certain superconductors.

Characterization of the thermodynamic and magnetic properties of this state.

Discussion of a first-order metamagnetic phase transition associated with the new phase.

Abstract

We propose that a new state with a fully gapless Fermi surface appears in quasi-2D multiband superconductors in magnetic field applied parallel to the plane. It is characterized by a paramagnetic moment caused by a finite density of states on the open Fermi surface. We calculate thermodynamic and magnetic properties of the gapless state for both s-wave and d-wave cases, and discuss the details of the 1-st order metamagnetic phase transition that accompanies the appearance of the new phase in s-wave superconductors. We suggest possible experiments to detect this state both in the s-wave (2-H NbSe2) and d-wave (CeCoIn5) superconductors.