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

Abstract

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 Néel temperature $T_{\mathrm{N}}$ = 2.2 K decreases with increasing pressure and becomes zero at the critical pressure $P_{\mathrm{AF}}$ $\simeq$ 0.6 GPa. On the other hand, the superconducting phase exists in a wider pressure region from ambient pressure to $P_{\mathrm{AF}}$ $\simeq$ 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. $C_{\mathrm{ac}}$ shows a bending structure at 1.98, 2.21, and 2.40 GPa .The temperatures where these anomalies are observed are close to the phase boundary of the FM3 phase.

This paper was presented at the international workshop ``Novel Pressure-induced Phenomena in Condensed Matter Systems(NP2CMS)" August 26-29 2006, Fukuoka Japan

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