Precursors of the insulating state in the square lattice Hubbard model

TL;DR

This study investigates the precursors to insulating behavior in the 2D square lattice Hubbard model using the ladder dual fermion approach, revealing non-local correlations, pseudogap formation, and the persistence of metallic phases at finite temperatures.

Contribution

It introduces the ladder dual fermion approach to analyze the Hubbard model, highlighting the role of non-local correlations and providing new insights into the crossover temperature and insulating precursors.

Findings

Non-local correlations lower potential energy and induce a pseudogap.

Self-energy shows precursors to an insulating phase.

Metallic phase persists at accessible temperatures.

Abstract

We study the two-dimensional square lattice Hubbard model for small to moderate interaction strengths $1\leq U/t\leq 4$ by means of the ladder dual fermion approach. The non-local correlations beyond dynamical mean-field theory lower the potential energy, lead to a maximum in the uniform susceptibility and induce a pseudogap in the density of states. While the self-energy exhibits precursors of a possible insulating phase linked to the appearance of long-range fluctuations, the metallic phase persists within the accessible temperature range. Finite-size effects affect results qualitatively. Upper bounds on the crossover temperature are found to be significantly lower than previously reported dynamical vertex approximation results at $U/t=1$.