Triple approach to determination of the c-axis penetration depth in BSCCO crystals

The c-axis penetration depth lambda (c) in Bi2Sr2CaCu2O8+delta (BSCCO) sing le crystals as a function of temperature has been determined using three hi gh-frequency techniques, namely (1) measurements of the ac-susceptibility a t a frequency of 100 kHz for different sample alignments with respect to th e ac magnetic field; (2) measurements of the surface impedance in both supe rconducting and normal states of BSCCO crystals at 9.4 GHz; (3) measurement s of the surface barrier field H-J(T) proportional to 1/lambda (c)(T) at wh ich Josephson vortices penetrate into the sample. Careful analysis of these measurements, including both numerical solution of the electrodynamic prob lem of the magnetic field distribution in an anisotropic plate at an arbitr ary temperature and influence of defects in the sample has allowed us to es timate lambda (c)(0) approximate to 50 mum in BSCCO crystals overdoped with oxygen (T-c approximate to 84 K) and lambda (c)(0) approximate to 150 mum at the optimal doping level (T-c approximate to 90 K). The results obtained by different techniques are in reasonable agreement.