Coulomb localization in orbital degenerate, doped Mott insulators

Adolfo Avella,Peter Horsch,Andrzej M Oleś

doi:10.1063/1.5042829

Abstract

We study electron localization in a three-band extended Hubbard model describing the t2g electrons of doped vanadium perovskites such as La1−xCaxVO3, where Ca defects are represented by Coulomb potentials. The main goal of this paper is to explore what happens when long-range electron-electron (e-e) interactions are switched on. The electronic structure of these doped Mott-Hubbard insulators is calculated using the unrestricted Hartree-Fock approximation that allows to perform the required statistical averages over many distinct defect realizations. The Mott gap is found to persist up to large doping and the defect states, appearing inside of it, are seen to develop a defect states gap centered at the Fermi energy. The internal kinetic energy of the doped holes, forming spin-orbital polarons bound to the defects, induces the defect states gap even in the absence of e-e interactions. Such kinetic gap survives disorder fluctuations and is amplified by long-range e-e interactions. A study of the inverse participation ratio reveals the small size of such spin-orbital polarons and provides an explanation for the persistence of spin and orbital order up to high doping.

Highlights

Doping Mott insulators has become a central topic of condensed matter physics with the discovery of high-T c superconductivity.[1]
We explore the effect of disorder of charged defects on the electronic excitations observed in the photoemission spectra of doped vanadium perovskites such as La1−xCaxVO3
Strong orbital quantum fluctuations (OQF) are a characteristic of the C-type AF (C-AF) spin and G-type alternating orbital (G-AO) ordered phase,[6] i.e., leading to a strong ferromagnetic (FM) exchange interaction along the c-axis

Summary

Introduction

Doping Mott insulators has become a central topic of condensed matter physics with the discovery of high-T c superconductivity.[1]. Characteristic for the vanadium d2 perovskites with partly filled t2g valence orbitals is the persistence of the Mott insulating state and of spin and orbital order up to high concentrations x of Ca ions and doped holes[2,3,4] in striking contrast to cuprate superconductors. In these latter, eg orbitals are largely split, and the doped holes, already at quite low concentrations, destroy the antiferromagnetic (AF) order and let the system metallize.[1].

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Conclusion