High-Magnetic-Field Lattice Length Changes in URu2Si2

We report high-magnetic-field (up to 45 T) (c) over cap -axis thermal-expansion and magnetostriction experiments on URu2Si2 single crystals. The sample length change Delta L-c(T-HO)/L-c associated with the transition to the "hidden order'' phase becomes increasingly discontinuous as the magnetic field is raised above 25 T. The reentrant ordered phase III is clearly observed in both the thermal expansion Delta L-c(T)/L-c and magnetostriction Delta L-c(B)/L-c above 36 T, in good agreement with previous results. The sample length is also discontinuous at the boundaries of this phase, mainly at the upper boundary. A change in the sign of the coefficient of thermal expansion alpha(c) = 1/L-c (partial derivative Delta L-c/partial derivative T) is observed at the metamagnetic transition (B-M similar to 38 T), which is likely related to the existence of a quantum critical end point. DOI: 10.1103/PhysRevLett.109.246405