Superconductivity in a model of two Hubbard chains coupled with ferromagnetic exchange interaction

TL;DR

This paper investigates the ground-state phases of a two-chain Hubbard model with ferromagnetic coupling, revealing density-dependent magnetic and pairing behaviors using advanced numerical methods.

Contribution

It provides a comprehensive phase diagram of the model, identifying dominant pairing correlations and magnetic states across different electron densities.

Findings

Spin gap opens at high electron density with dominant spin-singlet pairing.

Low electron density favors a fully polarized ferromagnetic state with spin-triplet pairing.

The phase diagram maps magnetic and pairing phases as functions of interaction strength and filling.

Abstract

We study the ground-state properties of the double-chain Hubbard model coupled with ferromagnetic exchange interaction by using the weak-coupling theory, density-matrix renormalization group technique, and Lanczos exact-diagonalization method. We determine the ground-state phase diagram in the parameter space of the ferromagnetic exchange interaction and band filling. We find that, in high electron density regime, the spin gap opens and the spin-singlet $d_{xy}$-wave-like pairing correlation is most dominant, whereas in low electron density regime, the fully-polarized ferromagnetic state is stabilized where the spin-triplet $p_{y}$-wave-like pairing correlation is most dominant.