Th 1Ϫx U x Cu 2 Si 2 compounds have been investigated by means of specific heat, susceptibility, magnetization, and resistivity measurements. Samples with xу0.15 are ferromagnetic. Th 0.85 U 0.15 Cu 2 Si 2 and Th 0.8 U 0.2 Cu 2 Si 2 show enhanced values for C/T at low temperatures ͑Ϸ460 mJ/U mol K 2 for xϭ0.2͒. The specific heat of samples that exhibit no long-range order ͑xр0.1͒ can be described by C/TϰϪln(T). This divergence is characteristic of non-Fermi-liquid ͑nFl͒ systems. The results are discussed in regard to the current investigations on non-Fermi liquids. One interpretation of non-Fermi-liquid behavior is a Tϭ0 instability in nearness to magnetism. Our data indicate that this is a system that displays C/Tϰln T near to ferromagnetism.

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We have grown epitaxial YBa2Cu3O7 films on GaAs using MgO buffer layers similar to Fork, Nashimoto, and Geballe [Appl. Phys. Lett. 60, 1621 (1992)]. However, the YBa2Cu3O7 was deposited by thermal coevaporation at an even lower substrate temperature of 620 °C. We obtained substantially improved quality [Tc=86.8 K, jc(77 K)=1.2×106 A/cm2, ρ(100 K)≤100 μΩ cm] and smooth surfaces free of outgrowth. An important aspect is preventing As contamination from the gas phase. This was achieved by encapsulating the free sample surface.

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