Critical fluctuations and phase diagram of La2−xSrxCuO4 thin films

We present a systematic study of the critical fluctuations of the superconducting to the normal-state transition of La2−xSrxCuO4 (LSCO) thin films with a wide range of hole concentrations (x = 0.07-0.20), which are probed by the frequency-dependent complex conductivity measurements and their dynamic scaling analyses. Our results clearly indicate that the critical dynamics of LSCO is essentially two-dimensional, except for the 3D-XY critical dynamics observed only near the optimally doped region. We argue possible origin of the anomalous dimensional crossovers with hole doping, including an implication of a hidden quantum critical point near the optimally doped region.