Upper Critical Magnetic Field of the Heavy-Fermion Superconductor UBe13

Abstract

The temperature dependence of the upper critical magnetic field $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ of the heavy-fermion superconductor U${\mathrm{Be}}_{13}$ was determined resistively. The magnitude of the initial slope of $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$, ∼420 kOe/K, is the largest value ever reported for a bulk superconductor. The curve of $H_{c2\mathrm{}}$ vs $T$ has an extremely unusual shape with a linear region that persists to very low temperatures. The anomalous shape of $H_{c2\mathrm{}}\mathrm{}\left(T\right)\mathrm{}$ cannot be accounted for by current theories of either conventional or $p$-wave superconductivity.