Suppression of the superconducting transition temperature T-c around x similar to 0.115 in La2-xSrxCuO4

Detailed studies of the superconducting diamagnetism of La2-x-yNdySrxCuO4 show that the characteristic concentration x(dip) at which the largest T-c suppression is observed changes from 0.115 to 0.125 on Nd doping around gamma similar to 0.12, above which the structural transition to the low-temperature tetragonal (LTT) phase is observed. This indicates that also in La2-xSrxCuO4, the x(dip) value is, in principle, also 1/8 as in La2-xBaxCuO4. We propose that the largest T-c suppression around x similar to 0.115 in La2-xSrxCuO4 is the result of the existence of two competitive factors. One is the local distortion expanding the LTT region around the Sr2+ ion, which is largest at x =1/8 and acts to suppress T-c. The other is ulr antiferromagnetic spin fluctuation energy, which might increase with x and acts to increase T-c. On Nd doping, the former factor becomes larger around x=0.125 than around x=0.115 and the x(dip) value moves to 0.125.