Competition of spatially inhomogeneous states in antiferromagnetic Hubbard model

TL;DR

This paper investigates the competition among various spatially inhomogeneous phases in the doped antiferromagnetic Hubbard model using mean-field theory, revealing nearly degenerate energies that challenge precise ground state predictions.

Contribution

It provides a comparative analysis of inhomogeneous phases' free energies in the doped Hubbard model, highlighting the difficulty in predicting the true ground state due to small energy differences.

Findings

All considered phases have very close free energies.

Small energy differences imply many factors influence phase stability.

Purely theoretical predictions of the ground state are unreliable.

Abstract

In this work we study zero-temperature phases of the anisotropic Hubbard model on a three-dimensional cubic lattice in a weak coupling regime. It is known that, at half-filling, the ground state of this model is antiferromagnetic (commensurate spin-density wave). For non-zero doping, various types of spatially inhomogeneous phases, such as phase-separated states and the state with domain walls ("soliton lattice"), can emerge. Using the mean-field theory, we evaluate the free energies of these phases to determine which of them could become the true ground state in the limit of small doping. Our study demonstrates that the free energies of all discussed states are very close to each other. Smallness of these energy differences suggests that, for a real material, numerous factors, unaccounted by the model, may arbitrary shift the relative stability of the competing phases. This further implies that purely theoretical prediction of the true ground state in a particular many-fermion system is unreliable.