Antiferromagnetic to superconducting phase transition in the hole- and electron-doped Hubbard model at zero temperature

TL;DR

This study uses a variational quantum-cluster approach to analyze the phase transition from antiferromagnetism to superconductivity in the Hubbard model, aligning well with experimental and Monte Carlo data.

Contribution

It introduces a thermodynamically consistent variational method to study phase competition in the Hubbard model, accurately reproducing key features of high-Tc cuprates.

Findings

Reproduces the high-Tc phase diagram including AF and SC phases.

Shows enhanced AF robustness with electron doping.

Identifies phase separation tendencies at low doping.

Abstract

The competition between d-wave superconductivity (SC) and antiferromagnetism (AF) in the high-Tc cuprates is investigated by studying the hole- and electron-doped two-dimensional Hubbard model with a recently proposed variational quantum-cluster theory. The approach is shown to provide a thermodynamically consistent determination of the particle number, provided that an overall shift of the on-site energies is treated as a variational parameter. The consequences for the single-particle excitation spectra and for the phase diagram are explored. By comparing the single-particle spectra with quantum Monte-Carlo (QMC) and experimental data, we verify that the low-energy excitations in a strongly-correlated electronic system are described appropriately. The cluster calculations also reproduce the overall ground-state phase diagram of the high-temperature superconductors. In particular, they include salient features such as the enhanced robustness of the antiferromagnetic state as a function of electron doping and the tendency towards phase separation into a mixed antiferromagnetic-superconducting phase at low-doping and a pure superconducting phase at high (both hole and electron) doping.