Evidence for a Novel State of Superconductivity in Noncentrosymmetric CePt₃Si: A ¹⁹⁵Pt-NMR Study

We report on novel antiferromagnetic (AFM) and superconducting (SC) properties of noncentrosymmetric CePt₃Si through measurements of the ¹⁹⁵Pt nuclear spin-lattice relaxation rate 1/T₁. In the normal state, the temperature (T) dependence of 1/T₁ unraveled the existence of low-lying levels in crystal-electric-field multiplets and the formation of a heavy-fermion (HF) state. The coexistence of AFM and SC phases that emerge at T_N=2.2   K and T_c=0.75   K, respectively, takes place on a microscopic level. CePt₃Si is the first HF superconductor that reveals a peak in 1/T₁ just below T_c and, additionally, does not follow the T³ law that used to be reported for most unconventional HF superconductors. We remark that this unexpected SC characteristic may be related to the lack of an inversion center in its crystal structure.