Defects, disorder and strong electron correlations in orbital degenerate, doped Mott insulators

TL;DR

This paper investigates how defect disorder and electron-electron interactions influence the spectral properties of doped Mott insulators, revealing regimes of soft gaps and pseudogaps with implications for understanding defect states in transition-metal oxides.

Contribution

It introduces a statistical framework using Weibull distribution to distinguish between soft gap and pseudogap regimes in doped Mott insulators considering defect disorder and electron interactions.

Findings

Soft gap of kinetic origin persists under certain conditions.

The Weibull shape parameter $k$ characterizes the gap regime.

Defect states preserve underlying spin and orbital order.

Abstract

We elucidate the effects of defect disorder and $e$-$e$ interaction on the spectral density of the defect states emerging in the Mott-Hubbard gap of doped transition-metal oxides, such as Y$_{1-x}$Ca$_{x}$VO$_{3}$. A soft gap of kinetic origin develops in the defect band and survives defect disorder for $e$-$e$ interaction strengths comparable to the defect potential and hopping integral values above a doping dependent threshold, otherwise only a pseudogap persists. These two regimes naturally emerge in the statistical distribution of gaps among different defect realizations, which turns out to be of Weibull type. Its shape parameter $k$ determines the exponent of the power-law dependence of the density of states at the chemical potential ($k-1$) and hence distinguishes between the soft gap ($k\geq2$) and the pseudogap ($k<2$) regimes. Both $k$ and the effective gap scale with the hopping integral and the $e$-$e$ interaction in a wide doping range. The motion of doped holes is confined by the closest defect potential and the overall spin-orbital structure. Such a generic behavior leads to complex non-hydrogen-like defect states that tend to preserve the underlying $C$-type spin and $G$-type orbital order and can be detected and analyzed via scanning tunneling microscopy.