Collective charge excitations and the metal-insulator transition in the square lattice Hubbard-Coulomb model

TL;DR

This paper investigates collective charge excitations and the metal-insulator transition in the square lattice Hubbard-Coulomb model using non-perturbative Monte Carlo simulations, revealing complex plasmon behavior and Hubbard band formation.

Contribution

It introduces a fully non-perturbative simulation approach and a modified Backus-Gilbert method to analyze spectral functions and charge excitations in the model.

Findings

Identification of non-trivial plasmon dispersion with two branches at strong coupling

Observation of Hubbard band formation in the density of states

Agreement with previous EDMFT studies on charge susceptibility behavior

Abstract

In this article, we discuss the non-trivial collective charge excitations (plasmons) of the extended square-lattice Hubbard model. Using a fully non-perturbative approach, we employ the hybrid Monte Carlo algorithm to simulate the system at half-filling. A modified Backus-Gilbert method is introduced to obtain the spectral functions via numerical analytic continuation. We directly compute the single-particle density of states which demonstrates the formation of Hubbard bands in the strongly-correlated phase. The momentum-resolved charge susceptibility is also computed on the basis of the Euclidean charge density-density correlator. In agreement with previous EDMFT studies, we find that at large strength of the electron-electron interaction, the plasmon dispersion develops two branches.