Frequency dependent conductivity in YBa2(Cu1−xZnx)3O7 thin films
- The complex AC conductivity of YBa_2(Cu_(1-x) Zn_x)_3 O_7 thin films has been investigated in the frequency range 10 Hz < v < 10^9 Hz and for temperatures 10 K <= T <= 300 K. The influence of the substrate material on the complex conductivity is studied in detail. In the normal conducting state no intrinsic frequency dependence of the real part of the conductivity sigma' could be detected, a finding which excludes a doping-induced localization of the charge carriers in this system. Below T_c, sigma'(T) reveals a coherence-like peak which has been predicted in the framework of the BCS theory. However, we propose that, in the doped superconductors, it is due to a distribution of T_c values. Finally, from the temperature dependence of the imaginary part of the conductivity we determine the T-dependence of the gap.
