Pseudogap, non-Fermi-liquid behavior, and particle-hole asymmetry in the 2D Hubbard model

TL;DR

This study investigates the pseudogap and non-Fermi-liquid behavior in the 2D Hubbard model using advanced numerical methods, revealing doping-dependent transitions and particle-hole asymmetry near the Mott transition.

Contribution

It introduces a mixed basis approach for more accurate self-energy calculations and characterizes the doping-driven transition from Fermi-liquid to non-Fermi-liquid states.

Findings

Non-Fermi-liquid behavior emerges below critical doping delta_c=0.15-0.20.

Particle-hole asymmetry increases as doping decreases.

Pseudogap formation correlates with spectral weight removal near E_F.

Abstract

The effect of doping in the two-dimensional Hubbard model is studied within finite temperature exact diagonalization combined with cluster dynamical mean field theory. By employing a mixed basis involving cluster sites and bath molecular orbitals for the projection of the lattice Green's function onto 2x2 clusters, a considerably more accurate description of the low frequency properties of the self-energy is achieved than in a pure site picture. The transition from Fermi-liquid to non-Fermi-liquid behavior for decreasing hole doping is studied as a function of Coulomb energy, next-nearest neighbor hopping, and temperature. In particular, the self-energy component Sigma_X associated with X=(pi,0) is shown to exhibit an onset of non-Fermi-liquid behavior as the hole doping decreases below a critical value delta_c. The imaginary part of Sigma_X(omega) then develops a collective mode above E_F, which exhibits a distinct dispersion with doping. Accordingly, the real part of Sigma_X(omega) has a positive slope above E_F, giving rise to an increasing particle-hole asymmetry as the system approaches the Mott transition. This behavior is consistent with the removal of spectral weight from electron states close to E_F and the opening of a pseudogap which increases with decreasing doping. The phase diagram reveals that delta_c = 0.15 ... 0.20 for various system parameters. For electron doping, the collective mode of Sigma_X(omega) and the concomitant pseudogap are located below the Fermi energy which is consistent the removal of spectral weight from hole states just below E_F. The critical doping which marks the onset of non-Fermi-liquid behavior, is systematically smaller than for hole doping.