Superconductivity recurrence and charge carrier compensation effect in La2−xSrxCu0.94M0.06O4 (M = Fe, Co and Ni) system

In this paper, the substitution effect of Sr for La in three non-superconducting system La2−xSrxCu0.94M0.06O4 (M = Fe, Co and Ni) have been systematically studied. As the concentration of Sr increases to around 0.20, the superconductivity is recovered. The peak at 695 cm−1 in the infrared spectra which is assigned to the stretching mode of oxygen atoms in plane induced by M3+ doping is suppressed by Sr increasing, demonstrating that the holes introduced by the Sr substitution have been injected into the CuO2 plane and compensate the localized electrons. These results suggest that the superconductivity recurrence is caused by the carrier compensation. The main origin of superconductivity suppression by the magnetic ions Fe/Co/Ni is the carrier localization effect.