  In underdoped YBa_2Cu_3O_x (YBCO) with x = 6.63, the opening of the pseudogap
at T^* ~ 160 K has a strong effect on the Hall angle tan(theta). While the Hall
response is significantly reduced, the diagonal current is relatively
unaffected. The Hall conductivity suppression continues deep into the flux-flow
state (from T_c to 40 K), as an anomalous suppression of the vortex Hall
current.
