^<13>C NMR in borocarbide superconductor

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Quaternary borocarbide intermetallic compounds RM_2B_2C (R = rare-earth element, M=transition metal element) show a relatively high superconducting transition temperature T_c The effect of electron correlation is expected to be important because the d-electron of transition metal plays a leading actor of conduction. From ^<13>C,^<11>B NMR,the detailed information on the electronic properties of borocarbide superconductor YNi_2B_2C is obtained in normal and superconducting state.1. In the normal state, the existence of the antiferromagnetic spin fluctuation was suggested. The spin-lattice relaxation rate T_1^<-1> and Knight shift K of ^<13>C and ^<11>B NMR show that the isotropic (Fermi contact) interaction between 2s conduction electron spin and nuclear spin at the carbon site and the boron site is dominant. The temperature dependences of T_1^<-1> and K is explained well by the Korringa mechanism. These temperature dependences are attributed to that of spin susceptibility, which is the consequence of band structure. No antiferromagnetic spin fluctuation is observed in ^<13>C and ^<11>B NMR.Strength of the electro-electron interaction is the same order as that found in alkali metal. These experimental results agree well with the results of band calculation.2. In the superconducting state, a small coherence (Hebel-Slichter) peak is obsereved, which testified the borocarbide compounds to be a conventional phonon-mediated s wave (BCS) superconductors. From the temperature dependence of <@D113@>D1CT<@D21@>D2<@D1-1@>D1, a superconducting gap parameter of 2DELTA<@D20@>D2/k<@D2B@>D2T<@D2C@>D2 = 3.30(]SY.+-。[)0.08 is obtained. The borocarbide compound being a conventional BCS superconductor is consistent with the normal properties of the Fermi liquid picture in the normal state.