Superconductivity in a spin liquid - a one dimensional example

TL;DR

This paper investigates a one-dimensional electron model showing that superconductivity can emerge due to interactions, with a divergent Cooper pair susceptibility, regardless of the sign of Hund's coupling.

Contribution

It demonstrates that superconductivity arises in a 1D model with specific interactions, independent of the sign of Hund's rule coupling, and characterizes the spectral gap and scaling dimensions.

Findings

Superconductivity occurs at T=0 with divergent Cooper pair susceptibility.

Spectral gaps stabilize the superconducting state against orbital hopping.

Scaling dimension of the order parameter varies between 1/4 and 1/2.

Abstract

We study a one-dimensional model of interacting conduction electrons with a two-fold degenerate band away from half filling. The interaction includes an on-site Coulomb repulsion and Hund's rule coupling. We show that such one-dimensional system has a divergent Cooper pair susceptibility at T = 0, provided the Coulomb interaction $U$ between electrons on the same orbital and the modulus of the Hund's exchange integral $|J|$ are larger than the interorbital Coulomb interaction. It is remarkable that the superconductivity can be achieved for {\it any} sign of $J$. The opening of spectral gaps makes this state stable with respect to direct electron hopping between the orbitals. The scaling dimension of the superconducting order parameter is found to be between 1/4 (small $U$) and 1/2 (large $U$).