We have performed low-temperature specific-heat measurements in magnetic fields for a single crystal UBe13. It has been observed that our sample exhibits a superconducting transition at an intermediate temperature (Tc ∼ 0.81 K) between previously reported values for two variant samples called H type and L type. The specific heat C(T) of our sample shows a T3 behavior below ∼0.7 Tc, which is similar to the behavior of the H-type sample, suggesting the existence of point nodes in the superconducting gap function. We have obtained the upper-critical-field curves Hc2 for the (001), (111), and (110) crystal axes, which show no anisotropy at least down to the lowest measured temperature of 0.5 K. We have also derived the Maki parameter k2, and it has been revealed that the k2 steeply decreases isotropically upon cooling just below T c. Paramagnetic effects and the symmetry of Cooper pairing of UBe13 are discussed.
- Heavy fermion
- Paramagnetic effect
- Unconventional superconductor