Charge ratchet from spin flip: space-time symmetry paradox

Abstract

Traditionally the charge ratchet effect is considered as a consequence of either the spatial symmetry breaking engineered
by asymmetric periodic potentials, or time asymmetry of the driving fields. Here we demonstrate that electrically and
magnetically driven quantum dissipative systems with spin-orbit interactions represent an exception from this standard
idea. In contrast to the so far well established belief, a charge ratchet effect appears when both the periodic potential
and driving are symmetric. We show that the source of this paradoxical charge ratchet mechanism is the coexistence of
quantum dissipation with the spin flip processes induced by spin-orbit interactions.