Thermodynamic Studies on Non Centrosymmetric Superconductors by AC Calorimetry under High Pressures

We investigated the non centrosymmetric superconductors CePt 3 Si and UIr by the ac heat capacity measurement under pressures. We determined the pressure phase diagrams of these compounds. In CePt 3 Si, the Neel temperature T N = 2.2 K decreases with increasing pressure and becomes zero at the critical pressure P AF ≃0.6 GPa. On the other hand, the superconducting phase exists in a wider pressure region from ambient pressure to P AF ≃1.5 GPa. The phase diagram of CePt 3 Si is very unique and has never been reported before for other heavy fermion superconductors. In UIr, the heat capacity shows an anomaly at the Curie temperature T C1 = 46 K at ambient pressure, and the heat capacity anomaly shifts to lower temperatures with increasing pressure. The present pressure dependence of T C1 was consistent with the previous studies by the resistivity and magnetization measurements. Previous ac magnetic susceptibility and resistivity measurements suggested the existence of three ferromagnetic phases, FM1-3. C ac s...