Scanning SQUID microscopy of superconducting La2−xSrxCuO4 single crystals

Abstract We have measured local magnetic images of La 2− x Sr x CuO 4 (LSCO) single crystals by the scanning SQUID microscope. For the LSCO single crystals with 0.11 x T c , as previously reported on LSCO thin film specimens, could not be detected presently. At around the optimally doped region, we found that the vortex patterns were clearly observed at 3 K though they totally diminished at temperatures higher than T c . Preliminary measurements on the “unique” underdoped LSCO single crystals, which have spatial Sr concentration gradient, revealed that the magnetic images changed at around x =0.12.