Normal state dynamical conductivity of layered superconductors

We have performed a model calculation of normal state macroscopic and micro scopic dynamical conductivity for layered superconductors, which consists o f one and two conducting layers per unit cell in the long-wavelength limit. Our calculation incorporates: (i) weak tunnelling of current between the l ayers; (ii) strong electron-electron interactions, which result in frequenc y- and temperature-dependent transport relaxation time; and (iii) optical p honons, which contribute to dynamical conductivity in the infrared frequenc y regime. Both the a-b plane and c-axis dynamical conductivity are calculat ed for longitudinal as well as transverse component of the field. It is fou nd that both intralayer and interlayer interactions contribute to dynamical conductivity of a layered superconductor. Our computed macroscopic conduct ivity as a function of frequency and temperature shows good agreement with experimental results on YBa-2Cu3O7 (YBCO). In agreement with prior reported detailed numerical calculations, our model calculation of the c-axis condu ctivity also shows a broad peak (which is attributed from tunnelling betwee n layers) in infrared frequency regime. We find that there exist one and tw o plasma modes, respectively in normal state of layered superconductors con sisting of one and two conducting layers per unit cell, both in the a-b pla ne and along c-axis. On the other hand, several transverse electric (TE) mo des are found to exist in a layered superconductor. One of the two plasma m odes in a layered superconductor having two conducting layers per unit cell is found to exist for wave vector values larger than the critical value de termined by intrinsic parameters of the superconductor. The complex frequen cy, which describes a plasma mode or a TE mode, consists of large imaginary part as compared to its real part. The frequency- and temperature-dependen t transport relaxation time, which is needed to obtain a good agreement bet ween theory and experiments, leads to larger imaginary part of complex freq uency and the broad peaks in microscopic dynamical conductivity. (C) 2000 P ublished by Elsevier Science B.V. All rights reserved.