Nodal-line pairing with 1D-3D coupled Fermi surfaces: a model motivated by Cr-based superconductors

TL;DR

This paper models a novel nodal-line superconducting state in Cr-based superconductors, showing how 1D-3D coupled Fermi surfaces induce unconventional gap structures with observable nodal rings.

Contribution

It introduces a two-band model with 1D-3D coupling, revealing how density fluctuations induce superconductivity and nodal rings, inspired by recent Cr-based superconductor discoveries.

Findings

Gap function peaks at Fermi sphere poles

Nodal rings form due to strong local repulsion

Results resemble experimental observations in Cr-based superconductors

Abstract

Motivated by the recent discovery of a new family of Chromium based superconductors, we consider a two-band model, where a band of electrons dispersing only in one direction interacts with a band of electrons dispersing in all three directions. Strong $2k_f$ density fluctuations in the one-dimensional band induces attractive interactions between the three-dimensional electrons, which, in turn makes the system superconducting. Solving the associated Eliashberg equations, we obtain a gap function which is peaked at the "poles" of the three-dimensional Fermi sphere, and decreases towards the "equator". When strong enough local repulsion is included, the gap actually changes sign around the "equator" and nodal rings are formed. These nodal rings manifest themselves in several experimentally observable quantities, some of which resemble unconventional observations in the newly discovered superconductors which motivated this work.