Frequency-dependent microwave conductivity of La2−xSrxCuO4 thin films

We report the frequency-dependent microwave conductivity, sigma(omega)=sigma1(omega)-isigma2(omega), of La2-xSrxCuO4 (LSCO) thin films in the frequency range between 45 MHz and 12 GHz. For LSCO films with x=0.04-0.07, which cross the phase boundary separating the insulating phase (x < 0.06) from the superconducting phase (x > 0.06), we observed a typical behavior of the Drude metal in the Hagen-Rubens limit above about 100 K. This suggests that the low-energy charge dynamics near the phase boundary is similar to that of the Drude metal, even if the doped holes self-organize into one-dimensional charge stripes. Moreover, for superconducting film with x=0.07, we observed a definite frequency-dependent feature in sigma(omega) near Tc, suggesting that the contribution of the superconducting fluctuation to sigma(omega) shows up.