Spontaneous quantum Hall effect in an atomic spinor Bose-Fermi mixture

TL;DR

This paper investigates a mixture of spinor bosons and fermions in an optical lattice, revealing that interactions induce various spin textures and a spontaneous quantum Hall effect in fermions, along with crystalline superfluidity in bosons.

Contribution

It demonstrates the emergence of a spontaneous quantum Hall effect and complex spin textures in a spinor Bose-Fermi mixture due to interactions and Fermi surface nesting.

Findings

Spontaneous formation of diverse spin textures in the ground state.

Observation of a spontaneous quantum Hall effect in fermions.

Detection of crystalline superfluidity in bosons.

Abstract

We study a mixture of spin-$1$ bosonic and spin-$1/2$ fermionic cold atoms, e.g., $^{87}$Rb and $^{6}$Li, confined in a triangular optical lattice. With fermions at $3/4$ filling, Fermi surface nesting leads to spontaneous formation of various spin textures of bosons in the ground state, such as collinear, coplanar and even non-coplanar spin orders. The phase diagram is mapped out with varying boson tunneling and Bose-Fermi interactions. Most significantly, in one non-coplanar state the mixture is found to exhibit a spontaneous quantum Hall effect in fermions and crystalline superfluidity in bosons, both driven by interaction.