Possible multipolar ordering in spin-orbital-entangled d2 system on a face-centred-cubic lattice

We propose to perform muon spin rotation (muSR) measurements on tungsten chlorides A2WCl6 (A = K, Rb, Cs) with a face-centred-cubic (FCC) lattice of W4+ ions. Because of strong spin-orbit coupling, W4+ ions have spin-orbital-entangled Jeff = 2 state. When the Jeff = 2 state is placed on a FCC lattice, the emergence of multipolar ordering such as charge quadrupole and magnetic octupole ordering is theoretically predicted. A2WCl6 do not show a clear sign of magnetic order down to 2 K, and a structural transition is seen at 180 K only for K2WCl6. Their magnetic ground state thus remains elusive. In order to distinguish the possible ground states such as magnetic (pseudo-dipolar or octupolar) order, spin-singlet state with charge quadrupolar order or spin-glass, temperature and magnetic field dependent muSR measurements will be conducted on the three compounds.