Magnetic susceptibility of normal state and superconductivity of La2−xSrxCuO4

Abstract The two-dimensional spin-correlation energy, J , was studied in La 2− x Sr x CuO 4 by means of magnetic susceptibility measurements .We found that J , deduced from the susceptibility peak temperature, T max , changed drastically with the character of the doped holes, localized or itinerant. In the low carrier density region (0≦ x ≦0.08), J was higher than 1000 K, representing the nearest neighbor interaction due to the localization of holes. A sudden drop of J and the appearance of bulk superconductivity were observed at x =0.09, which was ascribed to the itinerant holes. The Zn substitution effect for Cu was investigated near the superconductor-to-normal-metal transition. We found that only 1% Zn substitution resulted in 30% decrease of both T c and T max , and T max disappeared as T c became zero. Those results give us direct evidence that the spin correlation relates to the appearance of the superconductivity.