Ferromagnetism in tilted fermionic Mott insulators

TL;DR

This paper explores how tilting fermionic Mott insulators can induce a transition from antiferromagnetic to ferromagnetic interactions, with potential applications in quantum simulation and measurement.

Contribution

It demonstrates that large tilt in fermionic Mott insulators can switch the exchange interaction sign, revealing ferromagnetism via perturbation theory and numerical simulations.

Findings

Large tilt induces Wannier-Stark localization.

Exchange coupling sign changes to ferromagnetic.

Control of dynamics via tilt size.

Abstract

We investigate the magnetism in tilted fermionic Mott insulators. With a small tilt, the fermions are still localized and form a Mott-insulating state, where the localized spins interact via antiferromagnetic exchange coupling. While the localized state is naively expected to be broken with a large tilt, in fact, the fermions are still localized under a large tilt due to the Wannier-Stark localization and it can be regarded as a localized spin system. We find that the sign of the exchange coupling is changed and the ferromagnetic interaction is realized under the large tilt. To show this, we employ perturbation theory and real-time numerical simulation of the fermionic Hubbard chain. Our simulation exhibits that it is possible to effectively control the speed and time direction of the dynamics by changing the size of the tilt, which may be useful for experimentally measuring out-of-time-ordered correlators. Finally, we discuss experimental platforms, such as ultracold atoms in an optical lattice, to observe these phenomena.