De Haas–van Alphen Effect Studies on the Ferromagnetic Superconductor UGe2under High Pressure

Abstract

We have developed a clamped piston-cylinder high-pressure cell using NiCrAl alloy and have performed de Haas–van Alphen effect measurements on UGe 2 under hydrostatic pressures up to 17.6 kbar, which exceeds the critical pressure P c where the Curie temperature T C vanishes. We have found that a discontinuous change of the Fermi surface occurs across P c . Quasiparticle effective masses are substantially enhanced near 13 kbar, where the T x anomaly, which occurs below T C in the ferromagnetic phase, is suppressed. Heavy masses (∼40 m e ) are observed near P c on both the ferromagnetic and paramagnetic sides.