ANISOTROPY IN THE THERMAL-EXPANSION OF HEAVY-FERMION UPT3 AT THE SUPERCONDUCTING TRANSITION

We have measured the coefficients of linear thermal expansion (? and) of two single-crystalline samples of heavy-fermion UPt3 down to temperatures well below the superconducting transition (Tc0.5 K). The thermal expansion is strongly anisotropic at Tc, where only ? has a discontinuity. This implies that Tc is suppressed for a uniaxial stress along the hexagonal axis only. In the superconducting phase ? and vary approximately quadratically, with temperature, as does the specific heat. The Grüneisen parameter shows a large drop at Tc; from 69 in the normal phase to -10 in the superconducting phase. © 1990 The American Physical Society.