Vortex-state complex Hall conductivity of superconductingYBa2Cu3O7−δepitaxial films at radio frequencies

Abstract

The vortex-state complex Hall conductivity $({\ensuremath{\sigma}}_{\mathrm{xy}})$ of superconducting ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ epitaxial films is investigated from dc to radio frequencies $(\mathrm{u}\mathrm{p}\phantom{\rule{0ex}{0ex}}\mathrm{t}\mathrm{o}7\ifmmode\times\else\texttimes\fi{}{10}^{6}\mathrm{Hz})$, using a direct transport measurement technique. The experimental results are analyzed in terms of a model generalized from that for the dc Hall conductivity. This generalized model assumes that (1) the occurrence of sign reversal in the dc vortex-state Hall conductivity is the result of different carrier densities within and far away from the vortex core; (2) the Drude approximation is applicable; and (3) the anomalous sign reversal occurs in the flux-flow limit. We find that the temperature and frequency dependencies of our complex Hall conductivity data are in good agreement with our phenomenological model. In addition, when extended to higher frequencies, the same model provides consistent description for the complex Hall conductivity data at 100--800 GHz. Moreover, the magnetic-field (B) dependence of the complex Hall conductivity data reveals that both vortices $({\ensuremath{\sigma}}_{\mathrm{xy}}^{v})$ and quasiparticles $({\ensuremath{\sigma}}_{\mathrm{xy}}^{q})$ contribute to the vortex-state Hall conduction, where ${\ensuremath{\sigma}}_{\mathrm{xy}}^{v}\ensuremath{\propto}{B}^{\ensuremath{-}1}$ and ${\ensuremath{\sigma}}_{\mathrm{xy}}^{q}\ensuremath{\propto}B,$ in agreement with the model. The magnitude of the real part, ${\ensuremath{\sigma}}_{\mathrm{xy}}^{\ensuremath{'}},$ is also consistent with the theoretical estimate, while the magnitude of the imaginary part, ${\ensuremath{\sigma}}_{\mathrm{xy}}^{\ensuremath{''}},$ is significantly larger than the theoretical prediction. This discrepancy may be attributed to the unconventional electronic structures in vortices of cuprate superconductors with d-wave or mixed-pairing symmetries.