Measurement by EPR of the penetration depth in the high-Tc superconductors TlBa2Ca2Cu3Ox and Bi2Ca2SrCu2Ox

Abstract

Using a newly devleoped EPR spin-probing methodology, we have measured magnetic penetration depth λ for ${\mathrm{Tl}}_2$ ${\mathrm{Ba}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathit{x}}$ and ${\mathrm{Bi}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{SrCu}}_2$ ${\mathrm{O}}_{\mathrm{x}}$. The temperature dependence of λ is found to follow the relationship λ=${\lambda }_0$[1-(T/${\mathrm{T}}_{\mathit{c}}$ ${)}^4$ ${]}^{\mathrm{-}1/2}$, with ${\lambda }_0$=2520±100 Å and $T_c$=119 K for ${\mathrm{Tl}}_2$ ${\mathrm{BaCa}}_3$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7.8+\mathit{x}}$ and ${\lambda }_0$=2700±100 Å with $T_c$=84 K for ${\mathrm{Bi}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{SrCu}}_2$ ${\mathrm{O}}_{\mathrm{x}}$.