Linear ac magnetic response near the vortex-glass transition in single-crystalline YBa2Cu3O7.

Abstract

By using a miniature two-coil mutual-inductance method and an exact inversion scheme, the ac penetration depth ${\ensuremath{\lambda}}_{\mathrm{ac}}$ was measured in a twinned ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ crystal in dc fields parallel to the c axis. The Ohmic dc resistance was also measured on the same crystal. The behavior of these quantities was altogether consistent with the vortex-glass-transition scaling. However, if we calculate the Labusch parameter and the pinning relaxation time from ${\ensuremath{\lambda}}_{\mathrm{ac}}$, they show unexpectedly large frequency dependencies, which can hardly be explained by the standard theory of the linear ac response of pinned vortices.