Fluctuations in the Hall conductivity and dynamics of the order parameter in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ superconductors

Fluctuation contributions to the Hall and longitudinal conductivities in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ epitaxial films have been investigated. Two remarkable features were observed: (1) the fluctuation contribution to the Hall conductivity, ${\mathrm{\sigma }}_{\mathit{x}\mathit{y}}^{\mathrm{fl}}$, changes sign at temperatures ${\mathit{T}}^{\mathrm{*}}$(H)>${\mathit{T}}_{\mathit{c}}$(H=0) and (2) the ratio ${\mathrm{\sigma }}_{\mathit{x}\mathit{y}}^{\mathrm{fl}}$/${\mathrm{\sigma }}_{\mathit{x}\mathit{x}}^{\mathrm{fl}}$ where ${\mathrm{\sigma }}_{\mathit{x}\mathit{x}}^{\mathrm{fl}}$ is the fluctuation longitudinal conductivity, shows a sharp minimum near ${\mathit{T}}_{\mathit{c}}$(H). These features may reflect an unusual behavior of the imaginary part of the relaxation time of the order parameter in the vicinity of the transition temperature.