Double sign reversal of the vortex Hall effect in YBa2Cu3O7-delta thin films in the strong pinning limit of low magnetic fields

Measurements of the Hall effect and the resistivity in twinned YBa2Cu3O7-de lta thin films in magnetic fields B oriented parallel to the crystallograph ic c axis and to the twin boundaries reveal a double sign reversal of the H all coefficient for B much less than 1 T. In high transport current densiti es, or with B tilted off the twin boundaries by 5 degrees, the second sign reversal vanishes. The power-law scaling of the Hall conductivity to the lo ngitudinal conductivity in the mixed state is strongly modified in the regi me of the second sign reversal. Our observations are interpreted as strong, disorder-type dependent vortex pinning and confirm that the Hall conductiv ity in hightemperature superconductors is not independent of pinning.