Mixed-state Hall effect in high-temperature superconductors in small and large magnetic fields

In many higll-tempelature superconductors, the Hall effect in the mixed sup erconducting state has a sign opposite to that in the normal state. Some hi ghly anisotropic materials exhibit even a double sign reversal of the mixed -slate Mall effect. We investigate this anomaly in precisely-patterned thin films of YBa2Cu3O7-delta (YBCO) in a large range of magnetic fields from 3 2 mT to 13 T. The Hall conductivity appears to decompose into two contribut ions of different sign. The positive (hole-like) part increases steeply bel ow the critical temperature a,ld indicates that the scattering rate of the quasiparticles in the superconducting state is drastically reduced. The neg ative contribution is present around the critical temperature and becomes i mportant in low fields only. The delicate interplay between these two contr ibutions, together with the cutoff of the experimental window bg pinning, l eads to the various experimental observations, and eventually to a double s ign change in fields below 0.25 T that has not been observed previously in YBCO.