Ferrimagnetism of ultracold fermions in a multi-band Hubbard system

TL;DR

This paper investigates ferrimagnetic states in a Lieb lattice of ultracold fermions, revealing robust magnetic order and its evolution with interaction strength and lattice geometry, relevant for multi-orbital correlated systems.

Contribution

It demonstrates the emergence and robustness of ferrimagnetism in a multi-band Hubbard model on a Lieb lattice, connecting lattice tuning to magnetic phases.

Findings

Ferrimagnetic order observed at half-filling in a Lieb lattice.

Magnetic order persists across a range of interaction strengths.

Lattice geometry tuning influences the emergence of ferrimagnetism.

Abstract

Strongly correlated materials feature multiple electronic orbitals which are crucial to accurately understand their many-body properties, from cuprate materials to twisted bilayer graphene. In such multi-band models, quantum interference can lead to dispersionless bands whose large degeneracy gives rise to itinerant magnetism even with weak interactions. Here, we report on signatures of a ferrimagnetic state realized in a Lieb lattice at half-filling, characterized by antialigned magnetic moments with antiferromagnetic correlations, concomitant with a finite spin polarization. We demonstrate their robustness when increasing repulsive interactions from the non-interacting to the Heisenberg regime, and study their emergence when continuously tuning the lattice unit cell from a square to a Lieb geometry. Our work paves the way towards exploring exotic phases in related multi-orbital models such as quantum spin liquids in kagome lattices and heavy fermion behavior in Kondo models.