MICROSTRUCTURE AND TEMPERATURE DEPENDENCE OF MICROWAVE PENETRATION DEPTH OF Ag-YBa 2 Cu307-6 THIN FILMS Davinder Kaur and R.Pinto Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400 005, India ABSTRACT We report the measurements of the magnetic penetration depth X(T) of Ag-doped YBa 2 Cu 3 07_8 (YBCO) thin films in the film thickness range 1500-4000A and temperature range 18-88K. The films are insitu grown by laser ablation on LaAIO 3 <100> single crystal substrates. The penetration depth measurements are performed by microstrip resonator technique. A correlation of X(T) with the film microstructure observed with Atomic Force Microscopy has shown that %(T) depends critically on the film microstructure. Temperature dependence of X(T) has also been studied for best quality films.The experimental results are discussed in terms of BCS theory (s-wave pairing) and d-wave Pairing with and without impurity scattering. The results are found to be best fitted to the d-wave model in dirty limit with impurity scattering. Near Tc, we have also compare the (3D) XY critical regime and the Ginzburg-Landau (GL) behaviour. INTRODUCTION Measurement of the temperature dependence of magnetic penetration depth X(T) in high T, superconductors is of great interest since k is directly related to the pair density n,. The fundamental issue of the pair mechanism responsible for the high-Tc superconductors and of the corresponding pairing state is intimately related to the temperature dependence of the magnetic penetration depth. Various pairing states (whether s-wave or d-wave in clean and dirty limit) have been proposed for the cuprate superconductors which differentiates on the basis of the fact that whether or not there are nodes in the gap function. As a consequence there are varying behaviour of temperature dependence of X especially at low temperature for various pairing states. For s- wave BCS superconductor because of single sign energy gap, the temperature dependence of penetration depth shows exponentially activated behaviour with AX(T) oc exp (-A/KBT), where A is the minimum value of the energy gap over the fermi surface. For d-wave pairing states, the only nodes allowed are line nodes, distributed on the fermi surface in such a way that the penetration depth exhibits a linear temperature dependence at low temperature with AX(T) 0c T. However in case of d-wave pairing in dirty limit, impurity scattering can change the temperature dependence from T to T 2 [1,2]. Recently a number of experimental results and theoretical interpretation of the results strongly suggest a d-wave pairing state symmetry in the hole doped cuprate superconductors[3-7]. In the present study we report the temperature dependence of penetration depth measurements of Ag-doped YBCO thin films in the temperature range 18-88K using highly sensitive technique [10] based on measurements of the resonant frequency of microstrip resonator constructed using superconducting thin films. 275 Mat. Res. Soc. Symp. Proc. Vol. 526 © 1998 Materials Research Society