Phase-separated Ferromagnetism in Spin-imbalanced Fermi Atoms Loaded on an Optical Ladder: a DMRG study

TL;DR

This study uses DMRG to explore phase-separated ferromagnetism in spin-imbalanced Fermi atoms on an optical ladder, revealing conditions for ferromagnetic domain formation influenced by interactions and spin imbalance.

Contribution

It demonstrates the emergence of phase-separated ferromagnetism in a ladder Hubbard model with spin imbalance, extending Nagaoka's ferromagnetism to this geometry.

Findings

Large U and p induce fully spin-polarized domains.

Ferromagnetic regions are maximized by tuning interaction and imbalance.

Real-space images show energy gap-driven phase separation.

Abstract

We consider repulsively-interacting cold fermionic atoms loaded on an optical ladder lattice in a trapping potential. The density-matrix renormalization-group method is used to numerically calculate the ground state for systematically varied values of interaction U and spin imbalance p in the Hubbard model on the ladder. The system exhibits rich structures, where a fully spin polarized phase, spatially separated from other domains in the trapping potential, appears for large enough U and p. The phase-separated ferromagnetism can be captured as a real-space image of the energy gap between the ferromagnetic and other states arising from a combined effect of Nagaoka's ferromagnetism extended to the ladder and the density dependence of the energy separation between competing states. We also predict how to maximize the ferromagnetic region.