Stripe and Bubble Ratchets on Asymmetric Substrates

Abstract: We show that a variety of non-monotonic ratchet effects can arise when mesophase pattern-forming systems, which exhibit anisotropic crystal, stripe, and bubble reigmes, are coupled to one-dimensional asymmetric substrates under ac driving. The ratchet efficiency and direction of motion are determined by how well the mesophase morphology matches the periodicity and shape of the substrate. Stripe states that are aligned with the substrate show the strongest ratchet effect, large bubbles show a weak ratchet effect, and small bubbles show a strong ratchet effect with an efficiency that oscillates as a function of ac drive amplitude. We map out the different rectification phases as a function of the pattern morphology, substrate strength, and ac drive amplitude. The pronounced ratchet effects that we observe in some regimes can be exploited for pattern sorting in hard and soft matter systems.