Magnetism driven by fluctuations and frustration in synthetic triangular antiferromagnets with ultracold fermions in optical lattices

TL;DR

This paper proposes using ultracold fermions in optical lattices to simulate frustrated triangular antiferromagnets, revealing complex magnetic phases, a spin reorientation transition, and coexistence of different ordering phenomena driven by quantum and thermal fluctuations.

Contribution

It introduces a new cold atom platform for studying frustrated magnetism and predicts novel magnetic phases and transitions not previously observed in such systems.

Findings

Multiple nontrivial magnetic phases identified.

A spin reorientation transition driven by quantum order-by-disorder.

Coexistence of Berezinskii-Kosterlitz-Thouless physics and long-range order.

Abstract

Quantum simulators based on cold atomic gases can provide an ideal platform to study the microscopic mechanisms behind intriguing properties of solid materials and further explore novel exotic phenomena inaccessible by chemical synthesis. Here we propose and theoretically analyze a coherently coupled binary mixture of Fermi atoms in a triangular optical lattice as a promising realization of synthetic frustrated antiferromagnets. We perform a cluster mean-field plus scaling analysis to show that the ground state exhibits several nontrivial magnetic phases and a novel spin reorientation transition caused by the quantum order-by-disorder mechanism. Moreover, we find from Monte Carlo simulations that thermal fluctuations induce an unexpected coexistence of Berezinskii-Kosterlitz-Thouless physics and long-range order in different correlators. These predictions, besides being relevant to present and future experiments on triangular antiferromagnetic materials, can be tested in the laboratory with the combination of the currently available techniques for cold atoms.