Quantized vortices and diamagnetic precursor to the Meissner state in high-Tc superconductors

We report the magnetic imaging for underdoped and optimally-doped La2-xSrxCuO4 (LSCO) thin films on single substrates and nearly optimally-doped YBa2Cu3O7-x (YBCO) thin films on tricrystal substrates in the temperature range both below and above T-c using scanning SQUID microscopy. Below T-c, clear integer- and half-integer quantized vortices were observable. Above T-c, however, the inhomogeneous diamagnetic domains appeared. The local diamagnetic domains that led to the Meissner state were found in the broad temperature range for underdoped samples and in the narrow limited temperature range for optimally-doped samples. The results provide evidence that local diamagnetic domains are closely related to the pseudogap state. The continuous connection of the domain state above T-c with the state of a half-integer vortex at the tricritical point in the YBCO film below T-c also indicates that the diamagnetic domains are also closely related to the occurrence of d(x 2-y 2)-wave superconductivity.