Measurements of anisotropic characteristic lengths in YBCO films at microwave frequencies

Abstract

We used microwave self-resonant and magnetically modulated microwave absorption techniques to measure the London penetration depth, λ, and coherence length, ξ, in the direction parallel and perpendicular to the a–b plane of YBCO films. We found that both λ and ξ were anisotropic; it appeared that the value of λ∥(0) was about 1800 Å and λ⊥(86.5) about 26 000 Å, where λ∥ is the penetration depth for the applied microwave electric field parallel and λ⊥ perpendicular to the film plane (c-axis is perpendicular to the film plane). We deduced ξ∥ to be equal to 129 Å and ξ⊥ 40 Å at 86.5 K. The anisotropy factor γ we determined to be about 3.