Nonlocal Excitation Spectra in 2D Doped Hubbard Model

TL;DR

This study investigates the nonlocal excitation spectra of the 2D doped Hubbard model using a high-precision method, revealing persistent marginal Fermi-liquid behavior and a kink in the quasiparticle band relevant to high-temperature superconductors.

Contribution

It introduces a self-consistent projection operator method that accurately captures nonlocal correlations in the 2D Hubbard model, advancing understanding of its excitation spectra.

Findings

Verifies quantum Monte-Carlo results at finite temperatures.

Identifies a persistent marginal Fermi-liquid state at finite doping.

Discovers a kink in the quasiparticle energy band caused by antiferromagnetic correlations.

Abstract

Single-particle excitation spectra of the two-dimensional Hubbard model on the square lattice near half filling and at zero temperature are investigated on the basis of the self-consistent projection operator method. The method guarantees a high accuracy of the spectra with high energy and high momentum resolutions. It takes into account long-range intersite correlations as well as the strong on-site correlations. Effects of nonlocal excitations are clarified by comparing the results with those of the single-site approximation. The calculated spectra verify the quantum Monte-Carlo results for finite temperatures. The spectra at the Fermi level yield a hole-like Fermi surface in the underdoped region and an electron-like Fermi surface in the overdoped region. From a numerical analysis of the momentum dependent effective mass and self-energy, it is concluded that a marginal Fermi-liquid like state persists even at finite doping concentrations in the strongly correlated region because a van Hove singularity is pinned to the Fermi surface. It is also found that a kink structure appears in the quasiparticle energy band in the same region. The kink is shown to be caused by a mixing between the quasiparticle band and an excitation band with strong short-range antiferromagnetic correlations. These results suggest an explanation for some of the unusual properties of the normal state in high-$T_{\rm c}$ cuprates.