High-Field Fermi Surface Properties in the Low-Carrier Heavy-Fermion Compound URu2Si2

We performed the Shubnikov-de Haas (SdH) experiments of the low-carrier heavy-fermion compound URu2Si2 at high fields up to 34 T and at low temperatures down to 30 mK. All main SdH branches named alpha, beta, and gamma were observed for all the measured field-directions (H parallel to [001] -> [100], [100] -> [110] and [001] -> [110]), indicating that they are attributed to the closed Fermi surfaces with nearly spherical shapes. An anomalous split of branch alpha was detected for the field along the basal plane; the split immediately disappeared by tilting the field to [001] direction, implying a fingerprint of the hidden order state. High-field experiments reveal the complicated field-dependence of the SdH frequencies and the cyclotron masses due to the Zeeman spin-splitting associated with the Fermi surface reconstruction in the hidden order state with small carrier numbers. A new SdH branch named omega with a large cyclotron mass of 25 m(0) was detected at high fields above 23 T close to hidden order instabilities.