First-order transition switch-off of superconductivity in UGe2

The ac magnetic susceptibility, the thermal expansion and the magnetostriction were measured using a single crystalline sample of UGe2 under pressure. We find that as the field exceeds a transition field, where the system transforms from a high pressure phase (P>P-X) into a low pressure phase (P<P-X), the superconductivity steeply collapses within a transient region arising from the pressure inhomogeneity. We also estimate an accurate value of P-X in zero temperature limit and a pressure distribution around it. Using thus estimated quantity, we argue that the superconductivity (in zero magnetic field) below the critical pressure is not intrinsic but extrinsic due to the pressure inhomogeneity. (C) 2009 Elsevier B.V. All rights reserved.