Resonating Valence-Bond State in an Orbitally Degenerate Quantum Magnet with Dynamical Jahn-Teller Effect

TL;DR

This paper investigates a quantum magnet with orbital degeneracy, deriving a model that reveals a novel 'JT liquid phase' where spin, orbital, and Jahn-Teller effects lead to dynamic quantum states, potentially explaining experimental observations.

Contribution

The study introduces a quantum-dimer model incorporating dynamical Jahn-Teller effects and identifies a new 'JT liquid phase' in orbitally degenerate quantum magnets.

Findings

Identification of a 'JT liquid phase' with dynamic dimers and JT singlets

Derivation of a quantum-dimer model from the Hamiltonian including JT effects

Discussion of the phase's relevance to non-magnetic states in Ba3CuSb2O9

Abstract

Short-range resonating-valence bond states in an orbitally degenerate magnet on a honeycomb lattice is studied. A quantum-dimer model is derived from the Hamiltonian which represents the superexchange interaction and the dynamical Jahn-Teller (JT) effect. We introduce two local units termed "spin-orbital singlet dimer", where two spins in a nearest-neighbor bond form a singlet state associated with an orbital polarization along the bond, and "local JT singlet", where an orbital polarization is quenched due to the dynamical JT effect. A derived quantum-dimer model consists of the hopping of the spin-orbital singlet dimers and the JT singlets, and the chemical potential of the JT singlets. We analyze the model by the mean-field approximation, and find that a characteristic phase, termed "JT liquid phase", where both the spin-orbital singlet dimers and the JT singlets move quantum mechanically, is realized. Possible scenarios for the recently observed non magnetic-ordered state in Ba$_3$CuSb$_2$O$_9$ are discussed.