Griffiths phase-like exponents in the hidden-order state of URu2Si2

We report electrical resistivity, magnetic susceptibility, and specific heat measurements of high-quality URu₂Si₂ single crystals at ambient pressure, in the hidden-order (HO) region of the phase diagram. An amazing power-law behavior is observed, for both DC susceptibility and specific heat, establishing the Griffiths model for the HO phase. The Griffiths phase is characterized by residual short-range correlations on the collapse of the long-range large-moment antiferromagnetic (LMAFM) phase due to the dilution effects. The existence of cluster-like spins is intrinsic, as evidenced by the frequency dispersion of AC susceptibility and the relaxation of magnetoresistance. On account of the freezing of magnetic clusters, an unidirectional anisotropy of the resistivity in rotating magnetic fields is detected, which naturally explains any possible broken symmetries in tiny and clean crystals. In this manner, the HO phase of URu₂Si₂ is intimately related to the LMAFM phase. The proposal of Griffiths phase as an alternative of the HO phase is very promising, which may open a new route into the understanding of exotic electronic states in correlated matter.