Implications of Tc-Variation in UBe13 for a Possible Fulde–Ferrell–Larkin–Ovchinnikov Phase

We measure the heat capacity of a UBe13 sample with an unusually low Tc for a polycrystal. We find an upturn in the upper critical field Hc2(T) below about Tc/2, much as for higher-Tc samples. Comparing the critical fields in our sample and in samples with higher Tc's shows that the low temperature limit of Hc2 is proportional to Tc(H = 0), as expected if the upturn comes from an FFLO phase and strong coupling.