We report the first measurements of the magnetic-field penetration depth )~ in the heavy electron superconductor UBe13, performed using a SQUID magnetometer. We find the temperature dependence of 2(T)-2(0) to follow a T 2 law at low temperatures, giving further evidence of extreme gap anisotropy in this compound. We calculate the temperature dependence expected for a variety of anisotropic states, including those representing certain classes of "exotic" pairing. In general situations, the supercurrent is not parallel to the vector potential, and a more complicated field penetration takes the place of the normal Meissner effect. We argue that the data are consistent with an energy gap with point nodes on the Fermi surface but inconsistent with the large value of the Landau parameter F~ expected for a translationally invariant Fermi liquid with large effective mass.

%e report the observation of a T temperature dependence of the magnetic field penetration depth in UBel3 at low temperatures. %'e show that this behavior is consistent with an anisotropic gap function for an axial p-wave state. Our results further show that the Landau parameter F'l appears to be small.

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We have measured the specific heat of single crystals of the ambient-pressure superconductor P-(BEDT-TTF)213, abbreviated P-(ET}213, from 0.7 to 18 K in zero and applied magnetic fields. No bulk specificheat anomaly in the vicimty of T, was observed, although Meissner-effect measurements (HI( c ) performed on these same crystals yield a volume percent superconductivity of at least 25% at 0.8 K. %e find a y =24 k3 mJ/molK2, which is larger than the value for the only previously known ambient-pressure superconductor, the Se-based (TMTSF)2C104 (TMTSF denotes tetramethyltetraselenafulvalene).This difference is due primarily to the greater density of S atoms in P-(ET)213 compared to the density of Se atoms in (TMTSF)2ClO&. The response of the low-temperature specific heat to fields up to 10 T aligned along c' was 0 to 2 3%, in sharp contrast to previous reports of a 20'ir%) increase in the specific heat of (TMTSF)2C104 in a field of 2 T. No evidence for a high-field magnetic or insulating state similar to that observed in (TMTSF)2CIO4 was found for P-{ET)213. New results on the specific heat in applied fields for (TMTSF) 2C104 are presented.

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