Diamagnetic Precursor State in High-Tc Oxide Superconductors near Optimal Doping Using Scanning Superconducting Quantum Interference Device Microscopy

Magnetic images of high-Tc La1.85Sr0.15CuO4 (LSCO) and YBa2Cu3O7-y (YBCO) thin films near optimal doping observed by scanning superconducting quantum interference device (SQUID) microscopy are presented in the temperature range both below and above the transition temperature Tc. While the quantized vortices were observable below Tc, local diamagnetic domains that led to the Meissner state were found in the narrow limited temperature range above Tc. The result provides evidence that local diamagnetic domains are closely related to the pseudogap state and the d-wave superconductivity.