Hosted by: Mark Dean

The spatially anisotropic character of d-orbitals in transition metal compounds can lead to many and diverse 'quantum' phases of matter when spin orbit coupling is on equal footing with with electronic correlations. These phases include multi-polar orders, spin liquids, and/or spin orbitals liquids. The most celebrated example is the Kitaev model for j=1/2 Kramers doublets on the honeycomb lattice. When orbital degeneracy is introduced, the resulting orbital fluctuations open up many unexplored possibilities. In this seminar, I will introduce the cluster Mott insulating lacunar spinels as class of model materials where correlations, spin orbit coupling, and orbital degeneracy act in concert to produce several interesting magnetic phases. Following this, I will present a set of neutron scattering results on one member of this family: GaTa4Se8, a material that realizes j=3/2 model on the FCC lattice. We observe that the ground state of GaTa4Se8 is a spin-orbital dimer singlet phase and capture the collective magnetic excitations from that state. Intriguingly, the dimerization transition is preceded by a regime of dynamic vibronic fluctuations extending to temperatures four times higher than the global symmetry breaking transition. I will discuss these results in relation to the quadrupolar ordering transition recently proposed for the sister compound GaNb4Se8. Zoom Meeting https://bnl.zoomgov.com/j/1608389385?pwd=QWNXbnFTOXVyQkFBU2o3ZGFjZ2pIdz09&from=msft