Normal-state and superconducting properties of the heavy-fermion compoundUBe13in magnetic fields

Low-temperature measurements (200 mK≲T≲18 K) of the specific heat C(T) of polycrystalline ${\mathrm{UBe}}_{13}$ show that the normal-state electronic specific heat $C_n$($T_c$)/$T_c$ remains virtually constant at applied magnetic fields of B=1, 2, 4, and 8. Suggestions to explain the maintenance of the entropy balance between the normal and the superconducting state are discussed. With B=13 T, C(T) is decreased below 3 K compared to the zero-field data, and increased above this temperature. The entropy of the electron system increases linearly above 10 K without indication of saturation. The sharp discontinuity of C(T) at the transition to the superconducting state and the large dc Meissner effect measured in the same compound suggest that ${\mathrm{UBe}}_{13}$ is a very homogeneous superconductor [$B_{c2}$(0)apeq210 T]. From isothermal magnetization measurements at T=100 mK, we obtain $B_{c1}$apeq24.4 mT and, for the Ginzburg-Landau parameter, κapeq2100.