Frequency-dependent microwave conductivity of La 2− xSr xCuO 4 thin films

Abstract

We report the frequency-dependent microwave conductivity, σ( ω)= σ 1( ω)− iσ 2( ω), of La 2− x Sr x CuO 4 (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 σ( ω) near T c, suggesting that the contribution of the superconducting fluctuation to σ( ω) shows up.