A numerical study of multi-soliton configurations in a doped antiferromagnetic Mott insulator

TL;DR

This study uses first-principles Hartree-Fock calculations to explore multi-soliton configurations in doped antiferromagnetic Mott insulators, revealing how Coulomb interactions stabilize vortex pairs and influence electronic properties.

Contribution

It demonstrates the stabilization of charged vortex pairs via Coulomb repulsion and spin-flux effects, providing insights into the electronic structure and phases of doped Mott insulators.

Findings

Charged meron-antimeron pairs are stabilized over certain doping ranges.

Charge vortices produce mid-infrared absorption features.

Low doping favors tightly bound pairs, high doping leads to Fermi liquid instability.

Abstract

We evaluate from first principles the self-consistent Hartree-Fock energies for multi-soliton configurations in a doped, spin-1/2, antiferromagnetic Mott insulator on a two-dimensional square lattice. We find that nearest-neighbor Coulomb repulsion stabilizes a regime of charged meron-antimeron vortex soliton pairs over a region of doping from 0.05 to 0.4 holes per site for intermediate coupling 3 < U/t <8. This stabilization is mediated through the generation of ``spin-flux'' in the mean-field antiferromagnetic (AFM) background. Holes cloaked by a meron-vortex in the spin-flux AFM background are charged bosons. Our static Hartree-Fock calculations provide an upper bound on the energy of a finite density of charged vortices. This upper bound is lower than the energy of the corresponding charged stripe configurations. A finite density of charge carrying vortices is shown to produce a large number of unoccupied electronic levels in the Mott-Hubbard charge transfer gap. These levels lead to significant band tailing and a broad mid-infrared band in the optical absorption spectrum as observed experimentally. At very low doping (below 0.05) the doping charges create extremely tightly bound meron-antimeron pairs or even isolated conventional spin-polarons, whereas for very high doping (above 0.4) the spin background itself becomes unstable to formation of a conventional Fermi liquid and the spin-flux mean-field is energetically unfavorable. Our results point to the predominance of a quantum liquid of charged, bosonic, vortex solitons at intermediate coupling and intermediate doping concentrations.