Triplet and in-gap magnetic states in the ground state of the quantum   frustrated FCC antiferromagnet Ba2YMoO6
  The geometrically frustrated double perovskite Ba2YMoO6 is characterized by quantum s=1/2 spins at the Mo5+ sites of an undistorted face-centered cubic (FCC) lattice. Previous low-temperature characterization revealed an absence of static long-range magnetic order and suggested a non-magnetic spin-singlet ground state. We report new time-of-flight and triple-axis neutron spectroscopy of Ba2YMoO6 that shows a 28 meV spin excitation with a bandwidth of ~4 meV, which vanishes above ~125 K. We identify this as the singlet-triplet excitation out of a singlet ground state, and further identify a weaker continuum of magnetic states within the gap, reminiscent of spin-polaron states arising due to weak disorder. 
J. P. Carlo, J. P. Clancy, T. Aharen, Z. Yamani, J. P. C. Ruff, J. J.   Wagman, G. J. Van Gastel, H. M. L. Noad, G. E. Granr...
cond-mat.str-el