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We confirmed bulk-superconductivity of a ferromagnet UGe 2 by the specific heat measurement, together with the measurements of the electrical resistivity and ac susceptibility, in a pressure range from p = 1.0 to 1.5 GPa, where the Curie temperature T C (= 22-36 K) is still high, but another characteristic temperature T * is close to zero. In this pressure range, the heavy fermion state is found to be formed at low temperatures.Cerium and uranium compounds indicate a variety of phenomena including magnetic and quadrupolar ordering, heavy fermion and anisotropic superconductivity [1]. In these compounds, the RKKY interaction and the Kondo effect compete with each other. The former interaction enhances the long-range magnetic order, while the latter effect quenches the magnetic moments of localized f electrons. Most of the cerium and uranium compounds order magnetically, where the former interaction overcomes the latter effect. When the magnetic ordering temperature is low enough or close to zero, the heavy fermion state is formed at low temperatures. The conduction electrons in the heavy fermion state are highly different from bare electrons. They are interacting electrons, moving slowly in the crystal, which correspond to a large effective mass m * or a large electronic specific heat coefficient γ .When pressure p is applied to the cerium compounds with antiferromagnetic ordering such as CeIn 3 and CePd 2 Si 2 , the Néel tempereture T N shifts to lower temperatures, and the magnetic quantum critical point corresponding to the extrapolation T N → 0 is reached at p = p c [2]. Superconductivity appears around p c . Correspondingly, the heavy fermion state is formed as p approaches p c . This seems to be a general feature, although the sample quality is essentially important for the appearance of superconductivity. This is because superconductivity is most likely to be magnetically-mediated or of a non-s-wave type and then the breaking of Cooperpairs is mainly due to impurities and crystal defects.

The fourteen kinds of pressure-transmitting media were evaluated by the ruby fluorescence method at room temperature, 77 K using the diamond anvil cell (DAC) up to 10 GPa in order to find appropriate media for use in low temperature physics. The investigated media are a 1:1 mixture by volume of Fluorinert FC-70 and FC-77, Daphne 7373 and 7474, NaCl, silicon oil (polydimethylsiloxane), Vaseline, 2-propanol, glycerin, a 1:1 mixture by volume of n-pentane and isopentane, a 4:1 mixture by volume of methanol and ethanol, petroleum ether, nitrogen, argon, and helium. The nonhydrostaticity of the pressure is discussed from the viewpoint of the broadening effect of the ruby R(1) fluorescence line. The R(1) line basically broadens above the liquid-solid transition pressure at room temperature. However, the nonhydrostatic effects do constantly develop in all the media from the low-pressure region at low temperature. The relative strength of the nonhydrostatic effects in the media at the low temperature region is discussed. The broadening effect of the ruby R(1) line in the nitrogen, argon, and helium media are significantly small at 77 K, suggesting that the media are more appropriate for cryogenic experiments under high pressure up to 10 GPa with the DAC. The availability of the three media was also confirmed at 4.2 K.