Large-J approach to strongly coupled spin-orbital systems

TL;DR

This paper introduces a new method to analyze ground states and excitations in spin-orbital systems with strong relativistic effects, using a generalized large-J approach and Holstein-Primakoff expansion.

Contribution

It extends the effective J description to large values, enabling systematic analysis of spin-orbital entanglement in complex materials.

Findings

Applicable to Sr2IrO4 and vanadium spinels AV2O4

Provides a systematic 1/J expansion of the Hamiltonian

Captures spin-orbital entanglement effects in ground states

Abstract

We present a novel approach to study the ground state and elementary excitations in compounds where spins and orbitals are entangled by on-site relativistic spin-orbit interaction. The appropriate degrees of freedom are localized states with an effective angular momentum J. We generalize J to arbitrary large values while maintaining the delicate spin-orbital entanglement. After projecting the inter-site exchange interaction to the manifold of effective spins, a systematic 1/J expansion of the effective Hamiltonian is realized using the Holstein-Primakoff transformation. Applications to representative compounds Sr2IrO4 and particularly vanadium spinels AV2O4 are discussed.