Normal and superconducting properties of noncentrosymmetric heavy fermion CeRhSi ₃

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 (1.6K 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.