Evidence for Novel Pairing State in Noncentrosymmetric Superconductor CePt3Si: 29Si-NMR Knight Shift Study

We report the measurements of the ${}^{29}$Si Knight shift ${}^{29}K$ on the noncentrosymmetric heavy-fermion compound CePt${}_3$Si in which antiferromagnetism (AFM) with $T_{\mathrm{N}}=2.2$ K coexists with superconductivity (SC) with $T_c=0.75$ K. Its spin part ${}^{29}{K}_{\mathrm{s}}$, which is deduced to be $K_{\mathrm{s}}^c\ge 0.11$ and 0.16% at respective magnetic fields $H=2.0061$ and 0.8671 T, does not decrease across the superconducting transition temperature $T_c$ for the field along the c-axis. The temperature dependence of nuclear spin-lattice relaxation of ${}^{195}$Pt below $T_c$ has been accounted for by a Cooper pairing model with a two-component order parameter composed of spin-singlet and spin-triplet pairing components. From this result, it is shown that the Knight-shift data are consistent with the occurrence of the two-component order parameter for CePt${}_3$Si.