High-frequency fluctuational conductivity in YBa${}_2$Cu${}_3$O${}_{7-\delta }$

Abstract

We present measurements of the fluctuational excess conductivity at 48 GHz and 24 GHz in YBa${}_2$Cu${}_3$O${}_{7-\delta }$ films above the transition temperature. The measurements depart from the gaussian prediction for finite-frequency fluctuational conductivity. We focus on the region not too close to $T_c$, where the real part of the excess conductivity drops much faster than the prediction of the gaussian model. We calculate the dynamic excess conductivity within a Ginzburg-Landau approach. In the calculation we insert a short-wavelength cutoff of the order of the inverse coherence length, in order to suppress high-momentum modes. The excess conductivity of all samples measured can be described very well by the modified model.

RevTeX, 4 pages, 2 figures. To appear in J. Low Temp. Phys. (Proceedings of MOS 02 Conference, Hsinchu, Taiwan, 13-17/8/2002)