We report the pressure-induced superconductivity in the noncentrosymmetric heavy-fermion CeRhSi3. The superconductivity emerges above about 12 kbar even though the antiferromagnetic ordering persists. Furthermore, another anomaly is observed in the superconducting phase. The anomalous magnetic field-temperature phase diagram with a high upper critical field suggests that an unconventional superconductivity is realized in CeRhSi3.

We review the normal and superconducting properties in the noncentrosymmetric heavy-fermion CeRhSi 3 . In the normal state, CeRhSi 3 exhibits the antiferromagnetic order at low temperatures (1.6 K at ambient pressure) although its Kondo temperature is much higher than the ordering temperature T N . With applying pressure P, T N initially increases and subsequently decreases. The superconductivity arises at the pressures where the antiferromagnetic transition occurs. T N does not seem to fall to zero but becomes nearly constant with further application of pressure, and then T N vs P merges with the superconducting transition temperature T c vs P at 26 kbar where T c reaches the maximum. Nearly perfect magneticshielding associated with the superconductivity is observed below 26 kbar, suggesting that the bulk superconductivity is realized below T N . We observe an anomaly below T c in the resistivity as well as in the ac-susceptibility. The origin of the both anomalies seem to be the same but have not been clarified. The magnetic field-temperature (H-T) phase diagram of the superconducting state for fields along the tetragonal a-axis is unusual. It has a concave structure and the upper-critical-field H c2 at zero temperature exceeds the paramagnetic limiting field expected from the BCS model. The pressure dependence of H-T phase diagram implies that the paramagnetic effect exists and the effect is much reduced in CeRhSi 3 . This result is consistent with the theoretical prediction for the noncentrosymmetric superconductor.

We report the measurements of the de Haas-van Alphen (dHvA) effect for field ranges below and above the metamagnetic transition field (//m) in CeRu2Si2. The dHvA frequency branches and the effective masses ranging from 1.5A^7O to 120mo observed below Hm agree with the predictions of the itinerant / electron model, whereas those above Hm can be explained well with the localized / electron model. All the dHvA frequencies change abruptly around Hm-The effective masses decrease considerably around Hm and then continue to decrease with increasing field.

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We report measurements of the de Haas-van Alphen effect in ZrZn2 under hydrostatic pressures up to 21 kbar where the Curie temperature vanishes. The exchange splitting of a Fermi surface changes in behavior with increasing magnetic field, which is qualitatively consistent with the behavior of the high-field magnetization, suggesting the existence of a crossover between two distinct magnetic states. These and previously unexplained findings may be understood in terms of a p-T-B phase diagram qualitatively similar to that of the ferromagnetic superconductor UGe2.