## Fermi surface in the hidden-order state of URu_{2}Si_{2} under intense pulsed magnetic fields up to 81 T

After more than 20 years of investigations, the heavy-fermion system URu_{2}Si_{2} remains an unsolved issue due to its “hidden-order” phase developing below *T*_{0} = 17.5 K, for which the order parameter has still not been identified. Here, we have performed an intensive investigation of URu_{2}Si_{2} high-quality single crystals by measuring their resistivity in pulsed high magnetic 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. For **H** parallel to **c**, Fourier analyses of Shubnikov-de Haas oscillations show that *μ*_{0}*H*_{LT}^{ρ,max}, at which *ρ*_{x,x} is maximal, coincides with a sudden modification of the Fermi surface, while *H*^{∗}, where a kink of *ρ*_{x,x} is observed, lies in a regime where the Fermi surface is smoothly modified. 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*θ* law, *θ* being the angle between **H** and **c**.

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*_{λ} =1350 T and associated with a low effective mass of the order of the free electron mass, and (iii) no Fermi surface modification occurs up to 81 T.

These new results obtained using the unique extreme conditions offered at the LNCMI-T facility, i.e. long-duration pulsed fields higher than 80 T (at temperatures down to 1.4 K here) and temperatures down to 100 mK (at fields up to 60 T here), constitute a new step toward an understanding of the correlation between the hidden-order phase, the Fermi surface and the magnetic properties in URu_{2}Si_{2}.

**Reference:**

G. W. Scheerer, W. Knafo, D. Aoki, M. Nardone, A. Zitouni, J. Béard, J. Billette, J. Barata, C. Jaudet, M. Suleiman, P. Frings, L. Drigo, A. Audouard, T. D. Matsuda, A. Pourret, G. Knebel, and J. Flouquet, *Fermi surface in the hidden-order state of URu*_{2}Si_{2} under intense pulsed magnetic fields up to 81 T, Phys. Rev. B **89**, 165104 (2014).

**See also:**

G. W. Scheerer, Ph-D Thesis, Université de Toulouse

G. W. Scheerer, W. Knafo, D. Aoki, G. Ballon, A. Mari, D. Vignolles, and J. Flouquet, *Interplay of magnetism, Fermi surface reconstructions, and hidden order in the heavy-fermion material URu*_{2}Si_{2}, Phys. Rev. B **85**, 094402 (2012).