RAPID COMMUNICATION: Under-doped La2-xSrxCuO4 with x = 0.063-0.125: TSFZ growth of high-quality crystals and anomalous doping dependences of superconducting properties

A series of high-quality La2−xSrxCuO4 (LSCO) superconductor crystals in the under-doping region with x = 0.063, 0.07, 0.09, 0.10, 0.111 and 0.125 have been successfully prepared by the travelling-solvent floating-zone (TSFZ) technique. The crystals are large and free of subgrains and foreign phases. The high crystal quality has been revealed by double-crystal x-ray rocking curves and Rutherford backscattering spectrometry combined with ion-beam channelling effect. We find that the evolutions of the superconducting transition width and volume fraction as a function of carrier concentration exhibit interesting anomalies in the vicinity of some 'magic number' doping levels such as x = 1/42 ( = 0.0625) and 1/32 ( = 0.111). We argue that these behaviours are of intrinsic electronic origin.