Decoupled Spin Chains in Ba$_3$CuSb$_2$O$_9$

TL;DR

This paper investigates how spin and orbital interactions in Ba$_3$CuSb$_2$O$_9$ lead to a spin chain state, explaining experimental observations like specific heat and magnetic susceptibility.

Contribution

It introduces an effective Hamiltonian showing orbitally ordered ground state that isolates spin chains, providing a new understanding of the material's magnetic properties.

Findings

Orbitally ordered ground state isolates spin chains.

The model explains the linear specific heat at low temperatures.

Including defect effects matches experimental susceptibility data.

Abstract

Inspired by recent measurements on Ba$_3$CuSb$_2$O$_9$, we explore the interplay of spin and orbital degrees of freedom in a triangular lattice for possible spin liquid-like behaviour. Our effective Hamiltonian describes the magnetic Cu layer by considering superexchange paths along the intermediate O's. A mean field study of ordered states reveals an orbitally ordered ground state that isolates the spin degrees of freedom into spin chains. This scenario naturally explains the linear specific heat as $T\to 0$ and, by including the effects of additional defect Cu's sitting off the triangular planes, we find remarkable agreement with the measured magnetic susceptibility.