The de Haas-van Alphen effect in URu2Si2 under pressure

We carried out a de Haas-van Alphen (dHvA) experiment under pressure on a heavy-fermion superconductor, URu2Si2. The dHvA frequency, which corresponds to a nearly spherical Fermi surface, increases slightly with increasing pressure, while the corresponding cyclotron mass decreases considerably. Neither the dHvA frequency nor the cyclotron mass exhibit any abrupt change at the critical pressure of 1.5 GPa. The present result is thus inconsistent with a recent phase-separation proposal.