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Superconductivity under pressure in FeSe (T c ∼7.5 K) has been investigated using singlecrystal specimens through the measurements of DC magnetization and electrical resistivity.A characteristic three-step increase in T c has been found under hydrostatic pressure up to ∼34 K above 7 GPa. The structural transition from a tetragonal phase to an orthorhombic phase (T s ∼87 K) is found to disappear at P ∼2.3 GPa, above which T c increases rapidly, suggesting that the superconductivity is enhanced by the tetragonal environment. Under nonhydrostatic pressure, the increase in T c is suppressed and the superconductive volume fraction is considerably reduced above 2 GPa, probably owing to the breaking of the tetragonal lattice symmetry by the uniaxial stress. The intimate correlation between the enhanced (suppressed) superconductivity and the tetragonality (orthorhombicity) in the phase diagram is a common feature of FeSe and other iron-pnictide superconductors.

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The formation of the pseudogap in CeNiSn has been investigated by means of resistivity and specific-heat measurements in high magnetic fields. When the field is raised from 0 to 12 T along the orthorhombic a axis, the semiconductorlike behavior in the resistivity below 6 K disappears and the linear electronic term in the specific heat increases from 57 to 100 mJ/K2mol. However, no significant effect was observed for fields along the b and c axes up to 15 T. These results suggest an anisotropic suppression of the pseudogap, which can be interpreted as a result of strong spin polarization of the renormalized narrow band

Measurements of electrical resistivity ͑͒, dc magnetization ͑M͒, and specific heat ͑C͒ have been performed on layered oxide Li x CoO 2 ͑0.25Յ x Յ 0.99͒ using single-crystal specimens. The versus temperature ͑T͒ curve for x = 0.90 and 0.99 is found to be insulating but a metallic behavior is observed for 0.25Յ x Յ 0.71. At T S ϳ 155 K, a sharp anomaly is observed in the -T, M-T, and C / T-T curves for x = 0.66 with thermal hysteresis, indicating the first-order character of the transition. The transition at T S ϳ 155 K is observed for the wide range of x = 0.46-0.71. It is found that the M-T curve measured after rapid cool becomes different from that after slow cool below T F , which is ϳ130 K for x = 0.46-0.71. T F is found to agree with the temperature at which the motional narrowing in the 7 Li NMR linewidth is observed, indicating that the Li ions stop diffusing and order at the regular site below T F . The ordering of Li ions below T F ϳ 130 K is likely to be triggered and stabilized by the charge ordering in CoO 2 layers below T S .