Cu NMR Study in Single Crystal Bi_2Sr_2CaCu_2O_8 : Observation of Gapless Superconductivity

概要

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The normal and superconducting properties in single crystal Bi_2Sr_2CaCu_2O_8 (Bi2212) with T_C= 86 K have been investigated by systematic measurements of the ^<63>Cu Knight shift, ^<63>K(T) and the nuclear-spin-lattice relaxation time, T_1. In the normal state, the T-dependences of ^<63>K(T) and (T_1 T)^<-1> in Bi2212 share similar magnetic behaviors to the underdoped systems such as oxygen deficient YBa_2Cu_3O_<6+x> and YBa_2Cu_4O_8, namely, ^<63>K(T) decreases with lowering temperature and ^<63>(T_1 T)^<-1> has a peak above T_c. However, from the analyses of the anisotropy of 1/T_1 and the hyperfine field, Bi2212 is found to belong to the slightly over-doped region as in Tl_2Ba_2CuO_<6+x> and TlSr_2CaCu_2O_<8-x>. In the superconducting state, the finding of T_1 T= const. law far below T_c has revealed that the superconductivity is in a gapless regime, accompanied by the finite density of states at the Fermi level.
社団法人日本物理学会の論文
1994-03-15