Spin-Orbital Entanglement Emerging from Frustration in the Kugel-Khomskii Model

TL;DR

This paper explores the complex phase diagrams of the bilayer and monolayer Kugel-Khomskii model, revealing entangled spin-orbital phases and their thermal evolution, with implications for specific fluoride compounds.

Contribution

It introduces a mean-field cluster approach to analyze entangled phases in the Kugel-Khomskii model, including interlayer singlet and exotic entangled phases, and studies finite-temperature behavior.

Findings

Identification of interlayer singlet phase in fluoride K3Cu2F7.

Discovery of exotic entangled spin-orbital phases.

Finite-temperature transition from alternating-orbital ferromagnet to paramagnetic phase.

Abstract

We investigate the zero-temperature phase diagrams of the bilayer square-lattice Kugel-Khomskii ($d^9$) model involving entangled and singlet phases using mean-field cluster approach. This diagram includes interlayer singlet phase observed in fluoride K$_3$Cu$_2$F$_7$ and exotic entangled spin-orbital phases. For a monolayer case, realized in K$_2$CuF$_4$, we perform similar calculations in finite temperature and show that the alternating-orbital ferromagnet decays first to an entangled uniform ferromagnet and then to a paramagnetic phase. Published in: J. Phys.: Conf. Series 391, 012085 (2012).