Singlet ground state of the quantum antiferromagnet Ba 3CuSb 2O 9

Abstract

We present local probe results on the honeycomb lattice antiferromagnet Ba 3CuSb 2O 9. Muon spin relaxation measurements in a 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. © 2012 American Physical Society.