Superconductivity, antiferromagnetism and phase separation in the two-dimensional Hubbard model: A dual-fermion approach

TL;DR

This paper applies the dual-fermion method to the 2D Hubbard model, revealing the interplay of superconductivity, antiferromagnetism, and phase separation, and exploring density wave fluctuations.

Contribution

It introduces a dual-fermion approach to study phase diagrams and fluctuation effects in the 2D Hubbard model, including phase separation and unconventional charge density waves.

Findings

Antiferromagnetism and d-wave superconductivity are present in the phase diagram.

Phase separation occurs in the low doping regime near the Mott insulator.

No divergence of susceptibility for unconventional charge density wave is observed.

Abstract

The dual-fermion approach offers a way to perform diagrammatic expansion around the dynamical mean-field theory. Using this formalism, the influence of antiferromagnetic fluctuations on the self-energy is taken into account through ladder-type diagrams in the particle-hole channel. The resulting phase diagram for the (quasi-)two-dimensional Hubbard model exhibits antiferromagnetism and d-wave superconductivity. Furthermore, a uniform charge instability, i.e., phase separation, is obtained in the low doping regime around the Mott insulator. We also examine spin/charge density wave fluctuations including d-wave symmetry. The model exhibits a tendency towards an unconventional charge density-wave, but no divergence of the susceptibility is found.