ANISOTROPY OF THE UPPER CRITICAL-FIELD NEAR TC AND THE PROPERTIES OF URU2SI2 AND UBE13 IN THE NORMAL STATE

Simultaneous measurements of the electrical resistivity rho Seebeck coefficient S, and thermal conductivity k of URu2Si2 and UBe13 are carried out. For URu2Si2 a strong anomaly in the k(T) dependence near the temperature of the antiferromagnetic transition was observed. The thermal conductivity of UBe13 exhibits only a small (about 30%) change of the derivative dk/dT near 8-9 K, which may be related to an increase of the characteristic length of antiferromagnetic correlations below this temperature. Studying STM spectra in the normal and magnetic phase of a URu2Si2 single crystal we observed that the magnetic gap, partially opened at the Fermi surface below the Neel temperature, T(N) = 17.5 K, is strongly anisotropic: gapped states mainly correspond to the tetragonal ab-plane. Anisotropy of the upper critical field near T(c) (H < 4kOe), studied for URu2Si2 and UBe13 single crystals, was found to be in a good correspondence with the character of the antiferromagnetic transition.