Quantum oscillations in URu2Si2

We present results of studies of the quantum oscillatory magnetization and resistivity in URu2Si2. Evidence has been found for the existence of several pockets of the Fermi surface, but the major and thermodynamically important sheets remain unobserved. The observed quasiparticle masses are of moderate magnitude, as expected from the linear coefficient of the heat capacity, and roughly uniform, in contrast to the isostructural cerium analogue, CeRu2Si2, in which both light and heavy quasiparticles coexist. For one Fermi surface we have observed oscillations which appear to extend below the upper critical field into the superconducting mixed state.