High-temperature kinetic magnetism in triangular lattices

TL;DR

This paper investigates kinetic magnetism in triangular lattice Fermi-Hubbard models at strong interactions, revealing how doping and temperature influence magnetic correlations and polaron formation, with implications for moire TMDC materials and ultracold atom experiments.

Contribution

It provides a theoretical analysis of magnetic polarons and doping-dependent magnetism in triangular lattices, explaining recent experimental findings and proposing observable signatures in ultracold atom setups.

Findings

Hole doping leads to antiferromagnetic polarons due to kinetic frustration.

Electron doping induces Nagaoka ferromagnetic correlations from propagating doublons.

Magnetic polarons can be observed via three-point hole-spin correlations in ultracold atom experiments.

Abstract

We study kinetic magnetism for the Fermi-Hubbard models in triangular type lattices, including a zigzag ladder, four- and six-legged triangular cylinders and a full two-dimensional triangular lattice. We focus on the regime of strong interactions, $U\gg t$ and filling factors around one electron per site. For temperatures well above the hopping strength, the Curie-Weiss form of the magnetic susceptibility suggests effective antiferromagnetic correlations for systems that are hole doped with respect to $\nu=1$, and ferromagnetic correlations for systems with electron dopings. We show that these correlations arise from magnetic polaron dressing of charge carrier propagating in a spin incoherent Mott insulator. Effective interactions corresponding to these correlations can strongly exceed the magnetic super-exchange energy. In the case of hole doping, antiferromagnetic polarons originate from kinetic frustration of individual holes in a triangular lattice. In the case of electron doping, Nagaoka type ferromagnetic correlations are induced by propagating doublons. These results provide a theoretical explanation of recent experimental results in moire TMDC materials. To understand many-body states arising from antiferromagentic polarons at low temperatures, we study hole doped systems in finite magnetic fields. At low dopings and intermediate magnetic fields we find a magnetic polaron phase, separated from the fully polarized state by a metamagnetic transition. With decreasing magnetic field the system shows a tendency to phase separate, with hole rich regions forming antiferromagnetic spinbags. We demonstrate that direct observations of magnetic polarons in triangular lattices can be achieved in experiments with ultracold atoms, which allow measurements of three point hole-spin-spin correlations.