Temperature Dependence of the Lower Critical Field of UPt sub 3 Doped With Boron

Doping of a small amount of boron in UPt sub 3 produces samples possessing somewhat higher superconducting transition temperatures and lower residual resistivities ( rho sub 0 ). Performed were dc-magnetization measurements and determined was the lower critical field (H sub c1 ) of a B-doped, single-crystal of UPt sub 3 , along the b and c axes. A kink was observed in the temperature dependence of H sub c1 for both b and c directions. Also observed was a double transition in ZFC dc-magnetization experiments for the external field parallel to the b axis. This step in the shielding curve coincides with the kink in H sub c1 and the second peak in the specific heat measurements on the same sample. No such feature is observed with the field along the c axis. As an upward kink in H sub c1 cannot be due to different metallurgical phases in the sample, it might be interpreted as a manifestation of the anisotropic superconductivity in this material.