Challenges to high-Tc superconductivity in cuprates by exploring condensate properties

Abstract

In this paper, I introduce recent our results on superconductivity fluctuation measurement of high-Tc cuprate both for the hole-doped La2-xSrxCuO4 (LSCO) and the electron-doped La2-xCexCuO4 (LCCO). In hole doped LSCO, the universality class was found to change twice as a function of doping, starting from the 2D-XY, changing to the 3D XY and another 2D ‘unknown’ behavior. The results favors theoretical interpretations of the phase diagram of high-Tc cuprate which assume the existence of an additional hidden quantum critical point around at the optimum doping. In electron doped cuprate, the superconductivity fluctuation is 3D XY for all samples with different hole doping, which is in sharp contrast to the hole doped cuprate. Thus, the asymmetry of the phase diagram between the hole doped and the electron doped materials is another important key factor to judge the applicability of various theories on high-Tc superconductivity.Under finite magnetic fields, the scaling relation was valid only for weak fields, and for higher fields, aspects as vortices appeared. However, even at low temperatures, just above the first order phase transition, vortex picture alone cannot describe the data satisfactory. Thus, we need a unified theory for the description of a large superconductivity fluctuation under finite magnetic fields for high-Tc cuprates.Finally, I showed that our novel technique of fabricating high-Tc Josephson bridge junction using a small island of Fe was turned out to be very promising.