Mott transition, Widom line and pseudogap in the half-filled triangular lattice Hubbard model

TL;DR

This study investigates the finite-temperature Mott transition, Widom line, and pseudogap phenomena in the half-filled triangular lattice Hubbard model using advanced quantum Monte Carlo methods, revealing key features of the phase diagram.

Contribution

It demonstrates the existence of a Widom line extending above the Mott critical point and characterizes the momentum-dependent pseudogap near the transition.

Findings

Widom line identified in the phase diagram.

Pseudogap observed over a large region near the Mott transition.

Finite-temperature Mott transition is observable in the thermodynamic limit.

Abstract

The Mott transition is observed experimentally in materials that are magnetically frustrated so that long-range order does not hide the Mott transition at finite temperature. The Hubbard model on the triangular lattice at half-filling is a paradigmatic model to study the interplay of interactions and frustration on the normal-state phase diagram. We use the dynamical cluster approximation with continuous time auxiliary field quantum Monte Carlo to solve this model for 1, 4, 6, 12, and 16 site clusters with detailed analysis performed for the 6 site cluster. We show that a) for every cluster there is an inflection point in the double occupancy as a function of interaction, defining a Widom line that extends above the critical point of the first-order Mott transition; b) the presence of this line and the cluster size dependence argue for the observability of the Mott transition at finite temperature in the thermodynamic limit; c) the loss of spectral weight in the metal to Mott insulator transition as a function of temperature and for strong interactions is momentum dependent, the hallmark of a pseudogap. That pseudogap spans a large region of the phase diagram near the Mott transition.