London Penetration Depth of YBa2Cu3O7-δ

Abstract

We have measured the ac magnetic susceptibility of powdered YBa₂Cu₃O_7-δ as a function of temperature. The temperature dependence of the London penetration depth estimated from the susceptibility data is quite different from that expected by the BCS theory. The result is well reproduced by the empirical formula λ(T)=λ(0)(1-T/T _c)^-1/2, suggesting the existence of a gapless region on the Fermi surface in the high-T _c oxide superconductor.