  The nature of extended states in disordered tight binding models with a
constant imaginary vector potential is explored. Such models, relevant to
vortex physics in superconductors and to population biology, exhibit a
delocalization transition and a band of extended states even for a one
dimensional ring. Using an analysis of eigenvalue trajectories in the complex
plane, we demonstrate that each delocalized state is characterized by an
(integer) winding number, and evaluate the associated complex current. Winding
numbers in higher dimensions are also discussed.
