Fermi surface in the hidden-order state of URu2Si2 under intense pulsed magnetic fields up to 81 T
Résumé
We presentmeasurements of the resistivity rho(x,x) of URu2Si2 high-quality single crystals in pulsed highmagnetic fields up to 81 T at a temperature of 1.4 K and up to 60 T at temperatures down to 100 mK. For a field H applied along the magnetic easy axis c, a strong sample dependence of the low-temperature resistivity in the hidden-order phase is attributed to a high carrier mobility. The interplay between the magnetic and orbital properties is emphasized by the angle dependence of the phase diagram, where magnetic transition fields and crossover fields related to the Fermi surface properties follow a 1/cos theta law, theta being the angle between H and c. For H parallel to c, a crossover defined at a kink of rho(x,x), as initially reported in [Shishido, Phys. Rev. Lett. 102, 156403 (2009)], is found to be strongly sample dependent: its characteristic field mu H-0(*) varies from similar or equal to 20 T in our best sample with a residual resistivity ratio RRR = rho(x,x) (300 K)/rho(x,x) (2 K) of 225 to similar or equal to 25 T in a sample with a RRR of 90. A second crossover is defined at the maximum of rho(x,x) at the sample-independent low-temperature (LT) characteristic field mu 0H(rho,max)(LT) similar or equal to 30 T. Fourier analyses of Shubnikov-de Haas oscillations show that H-rho,max(LT) coincides with a sudden modification of the Fermi surface, while H-* lies in a regime where the Fermi surface is smoothly modified. For H parallel to a, (i) no phase transition is observed at low temperature and the system remains in the hidden-order phase up to 81 T, (ii) quantum oscillations surviving up to 7 K are related to a new orbit observed at the frequency F-lambda similar or equal to 1350 T and associated with a low effective mass m(lambda)(*) = (1 +/- 0.5) m(0), where m(0) is the free electron mass, and (iii) no Fermi surface modification occurs up to 81 T.