c-axis penetration depth in Bi\(_2\)Sr\(_2\)CaCu\(_2\)O\(_{8+\delta}\) single crystals measured by ac-susceptibility and cavity perturbation technique

Abstract

The \(c\)-axis penetration depth \(\Delta\lambda_c\) in Bi\(_2\)Sr\(_2\)CaCu\(_2\)O\(_{8+\delta}\) (BSCCO) single crystals as a function of temperature has been determined using two techniques, namely, measurements of the ac-susceptibility at a frequency of 100 kHz and the surface impedance at 9.4 GHz. Both techniques yield an almost linear function \(\Delta\lambda_c(T)\propto T\) in the temperature range T<0.5 T_c. Electrodynamic analysis of the impedance anisotropy has allowed us to estimate \(\lambda_c(0)\approx 50 \mu\)m in BSCCO crystals overdoped with oxygen (\(T_c\approx 84\) K) and \(\lambda_c(0)\approx 150 \mu\)m at the optimal doping level (\(T_c\approx 90\) K).