Unusual 1/${\mathit{T}}^3$ temperature dependence of the Hall conductivity in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$

Measurements of the Hall coefficient ${\mathit{R}}_{\mathit{H}}$ and resistivity ${\mathrm{\rho }}_{\mathit{a}}$ of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ disclose anomalies in their temperature (T) dependences. The 1/${\mathit{R}}_{\mathit{H}}$ vs T curve has a negative curvature, while d${\mathrm{\rho }}_{\mathit{a}}$/dT displays a previously unreported step near 290 K. The Hall conductivity ${\mathrm{\sigma }}_{\mathit{H}}$ follows an unusual 1/${\mathit{T}}^3$ dependence from 100 to 360 K. We contrast the results with predictions of conventional Bloch theory, and compare them with recent calculations based on large-U models. Implications for cyclotron damping at low T are discussed.