Itinerant ferromagnetism in the repulsive Hubbard chain with anisotropic odd-wave attraction

TL;DR

This paper studies how anisotropic nearest-neighbor attraction induces itinerant ferromagnetism in a Hubbard chain, revealing critical attraction strengths and domain structures relevant to cold-atom experiments.

Contribution

It introduces a detailed analysis of ferromagnetism emergence in a Hubbard chain with anisotropic attraction, using DMRG, and connects findings to cold-atom setups with spin conservation.

Findings

Ferromagnetism appears at a critical attraction strength.

Partially and fully ferromagnetic states are identified.

Domain structures depend on attraction strength and trapping potential.

Abstract

The ground-state properties of the Hubbard chain with on-site repulsion and anisotropic nearest-neighbor attraction are investigated by means of density matrix renormalization group calculations. The non-local attraction acts between fermions of one spin component only, mimicking the effect of p-wave Feshbach resonances in cold-atom systems. We analyze the onset of itinerant ferromagnetism, pinpointing the critical attraction strength where partially and fully ferromagnetic states occur. In the cold-atom setup, where the two (pseudo) spin populations are separately conserved, ferromagnetism occurs with the nucleation of a fully imbalanced band-insulating domain hosting the attractive component only. The size of this domain grows with the attraction strength, therefore increasing the (opposite) imbalance of the other domain, until the two spin components are fully separated. In the presence of a harmonic trap, the ferromagnetic state hosts a partially imbalanced domain in the center with an excess of the attractive component and filling lower than one. This central region is surrounded by fully imbalanced domains, located in the trap tails, hosting only fermions belonging to the other component.