The low-temperature highly correlated quantum phase in the charge-density-wave 1T-TaS2 compound

A prototypical quasi-2D metallic compound, 1T-TaS2 has been extensively studied due to an intricate interplay between a Mott-insulating ground state and a charge-density-wave order. In the low-temperature phase, 12 out of 13 Ta4+ 5d-electrons form molecular orbitals in hexagonal star-of-David patterns, leaving one 5d-electron with S = 1/2 spin free. This orphan quantum spin with a large spin-orbit interaction is expected to form a highly correlated phase of its own. And it is most likely that they will form some kind of a short-range order out of a strongly spin-orbit coupled Hilbert space. In order to investigate the low-temperature magnetic properties, we performed a series of measurements including neutron scattering and muon experiments. The obtained data clearly indicate the presence of the short-ranged phase and put the upper bound on similar to 0.4 mu B for the size of the magnetic moment, consistent with the orphan-spin scenario.