Flux-flow Hall effect in superconducting ${\mathrm{Tl}}_2$${\mathrm{Ba}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$ films

In both high-${\mathit{T}}_{\mathit{c}}$ and low-${\mathit{T}}_{\mathit{c}}$ superconductors, the Hall effect in the mixed state often shows a sign reversal below ${\mathit{T}}_{\mathit{c}}$ that contradicts standard theories for flux-vortex motion. We have measured the mixed-state Hall effect in high-quality superconducting films of ${\mathrm{Tl}}_2$ ${\mathrm{Ba}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$, and find that the Hall angle α below ${\mathit{T}}_{\mathit{c}}$ consists of two components: A field-independent component exhibits a complicated temperature dependence, including a sign change near ${\mathit{T}}_{\mathit{c}}$, while a second component with very weak temperature dependence is linear in field and resembles the normal-state Hall angle. The field independence of the sign-reversing component is evidence for vortex motion, and can be understood in terms of simple drag forces acting on vortices.