Penetration of Josephson vortices and measurement of the c-axis penetration depth in $Bi_{2}Sr_{2}CaCu_{2}O_{8+\delta}$: Interplay of Josephson coupling, surface barrier and defects

The first penetration field H J ( T ) of Josephson vortices is measured through the onset of microwave absorption in the locked state, in slightly overdoped Bi 2 Sr 2 CaCu 2 O 8+ δ single crystals ( T c ≈ 84 K ). The magnitude of H J ( T ) is too large to be accounted for by the first thermodynamic critical field H c 1 ( T ). We discuss the possibility of a Bean-Livingston barrier, also supported by irreversible behavior upon flux exit, and the role of defects, which relates H J ( T ) to the c -axis penetration depth λ c ( T ). The temperature dependence of the latter, determined by a cavity perturbation technique and a theoretical estimate of the defect-limited penetration field are used to deduce from H J ( T ) the absolute value of λ c (0) = (35 ± 15) µm .