We report measurements of the temperature dependence of the magnetic penetration depth in different quality polycrystalline samples of noncentrosymmetric LaNiC 2 down to 0.05 K. This compound has no magnetic phases and breaks timereversal symmetry. In our highest quality sample we observe a T 2 dependence below 0.4T c indicative of nodes in the energy gap. We argue that previous results suggesting conventional s-wave behavior may have been affected by magnetic impurities.

We report the discovery of a superconductor LuGe 2 . Magnetic and electrical measurements showed that the transition temperature T c = 2.6± 0.1 K. Powder x-ray diffraction patterns indicate that this compound has the orthorhombic ZrSi 2 -type structure with space group C mcm . A refinement of the lattice parameters of the unit cell, determing by the method of least squares using the thirteen intense reflections for 2 Ͻ 60°, showed that a = 0.3969͑9͒, b = 1.5553͑3͒, and c = 0.3839͑9͒ nm. In addition, no superconducting transition above 1.8 K was observed for the nonstrochiometric compound LuGe 1.5 with AIB 2 -type structure.

As observed with x-ray powder diffraction, the orthorhombic structure of the parent compound LaNiC2 is retained in La(Ni1−xCux)C2 up to the solubility limit near x = 0.2. The refined lattice parameters show that both the c-axis and the volume of the unit cell v expand clearly, while the a- and b-axes show less percentage change due to doping with copper. These results are inconsistent with what one would expect from a chemical pressure effect. The change in Tc with x is similar to the change in the lattice parameters (c and v) with x and is consistent with the assumption that Cu has finite solubility in this system. Magnetic measurements indicate that the increase in Tc is initially rapid (dTc/dx = 12 K) but slows down (dTc/dx = 1 K) for x≥0.2 in the system La(Ni1−xCux)C2. As expected from the BCS theory, the Cu doping in this system may affect not only the density of state N(EF), but also the electron–phonon coupling parameter.

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