Exotic Spin-Orbital Physics in Hybrid Oxides

TL;DR

This paper investigates how different types of impurities affect spin-orbital interactions in a $4d^4$ Mott insulator, revealing that charge dilution can significantly alter orbital patterns at low doping levels.

Contribution

It introduces a comparative analysis of spin-orbital super-exchange effects caused by $3d$ impurities with various configurations in a $4d^4$ Mott insulator, highlighting the impact of charge dilution on orbital fluctuations.

Findings

Impurities can act as spin defects or generate orbital polarons.

Charge dilution introduces terms that enhance orbital fluctuations.

Low doping levels can radically change orbital patterns.

Abstract

We compare the effective spin-orbital super\-exchange triggered by magnetic $3d$ impurities with $d^3$ and $d^2$ configurations and either no orbital degree of freedom (orbital dilution) or hole replacing a doublon (charge dilution) in a $4d^4$ Mott insulator with $S=1$ spins. Impurities causing orbital dilution act either as spin defects decoupled from the surrounding ions, or generate orbital polarons along $d^3$-$d^4$ hybrid bonds. The exchange on these bonds determines which orbital is occupied by a doublon on the host site. In case of charge dilution by $3d^2$ impurities additional $\propto T_i^+T_j^+$ terms arise which enhance orbital fluctuations. We show that such terms may radically change orbital pattern at relatively low doping by $x=1/8$ hole defects. Our findings provide new perspective for future theoretical and experimental studies of doped transition metal oxides.