Mott insulating states with competing orders in the triangular lattice Hubbard model

TL;DR

This study investigates the complex phases of the triangular lattice Hubbard model, revealing how competing magnetic orders and thermodynamic properties evolve with interaction strength using multiple advanced computational methods.

Contribution

It combines tensor network, diagrammatic Monte Carlo, and dynamical mean-field techniques to comprehensively analyze the model's thermodynamics and magnetic correlations across different coupling regimes.

Findings

Insulating state exhibits high entropy at intermediate temperatures.

Double occupancy shows a minimum as temperature varies, indicating Pomeranchuk effect.

Intermediate coupling regime features both chiral and stripy antiferromagnetic correlations.

Abstract

The physics of the triangular lattice Hubbard model exhibits a rich phenomenology, ranging from a metal-insulator transition, intriguing thermodynamic behavior, and a putative spin liquid phase at intermediate coupling, ultimately becoming a magnetic insulator at strong coupling. In this multimethod study, we combine a finite-temperature tensor network method, minimally entangled thermal typical states (METTS), with two Green-function-based methods, connected-determinant diagrammatic Monte Carlo and cellular dynamical mean-field theory, to establish several aspects of this model. We elucidate the evolution from the metallic to the insulating regime from the complementary perspectives brought by these different methods. We compute the full thermodynamics of the model on a width-four cylinder using METTS in the intermediate to strong coupling regime. We find that the insulating state hosts a large entropy at intermediate temperatures, which increases with the strength of the coupling. Correspondingly, and consistently with a thermodynamic Maxwell relation, the double occupancy has a minimum as a function of temperature which is the manifestation of the Pomeranchuk effect of increased localization upon heating. The intermediate coupling regime is found to exhibit both pronounced chiral as well as stripy antiferromagnetic spin correlations. We propose a scenario in which time-reversal symmetry-broken states compete with stripy-spin states at lowest temperatures.