Singlet Ground State of the Quantum Antiferromagnet Ba3CuSb2O9

TL;DR

This study investigates the magnetic ground state of Ba3CuSb2O9, revealing a non-frozen, gapped quantum antiferromagnetic state with no spin freezing down to very low temperatures.

Contribution

It provides experimental evidence for a singlet ground state in Ba3CuSb2O9 using muon spin relaxation and NMR, highlighting the absence of spin freezing and the presence of gapped excitations.

Findings

No spin freezing down to 20 mK

Intrinsic susceptibility peaks at 55 K and drops to zero

Presence of gapped magnetic excitations

Abstract

We present local probe results on the honeycomb lattice antiferromagnet Ba3CuSb2O9. Muon spin relaxation measurements in zero field down to 20 mK show unequivocally that there is a total absence of spin freezing in the ground state. Sb NMR measurements allow us to track the intrinsic susceptibility of the lattice, which shows a maximum at around 55 K and drops to zero in the low-temperature limit. The spin-lattice relaxation rate shows two characteristic energy scales, including a field-dependent crossover to exponential low-temperature behavior, implying gapped magnetic excitations.