Hall effect signatures of electronic structure change near a field induced quantum critical point in U(Ru1-xRhx)2Si2

We investigate the Hall coefficient R-H, resistivity, and magnetization of URu2Si2, and U(Ru0.96Rh0.04)(2)Si-2 in the high field regime up to 45 T to trace the electronic structure changes in both high and low temperature regimes. We find that at high temperatures above similar to 7 K, temperature- and field-dependent positions of R-H maxima and magneto resistance maxima coincide with a coherent temperature T-coh at each field. These systematically decrease in temperatures with increasing fields and extrapolate to zero at the field-induced putative quantum critical point (QCP). This observation suggests a collapse of a new energy scale, i.e., a coherent temperature of a heavy quasiparticle band, at the putative field-induced QCP. At lower temperatures, we show there are discontinuous changes of the Hall number n(H) = 1/R(H)e at the phase boundaries. This behavior illustrates that the phase formation is caused by first order reconstructions of the Fermi surface, which we interpret to the polarization of Fermi surface pockets seen in de-Haas van-Alphen (dHvA) measurements. (C) 2007 Elsevier B.V. All rights reserved.