Abstract
We study the dynamics of vortices in an asymmetric (i.e., consisting of triangular cells) ring channel driven by an external ac current $I$ in a Corbino setup. The asymmetric potential rectifies the motion of vortices and induces a net vortex flow without any unbiased external drive, i.e., the ratchet effect. We show that the net flow of vortices strongly depends on vortex density and frequency of the driving current. Depending on the density, we distinguish a ``single-vortex'' rectification regime (for low density, when each vortex is rectified individually) determined by the potential-energy landscape inside each cell of the channel (i.e., ``hard'' and ``easy'' directions) and ``multi-vortex,'' or ``collective,'' rectification (high-density case) when the inter-vortex interaction becomes important. We analyze the average angular velocity $\ensuremath{\omega}$ of vortices as a function of $I$ and study commensurability effects between the numbers of vortices and cells in the channel and the role of frequency of the applied ac current. We have shown that the commensurability effect results in a stepwise $\ensuremath{\omega}\ensuremath{-}I$ curve. Besides the ``integer'' steps, i.e., the large steps found in the single-vortex case, we also found ``fractional'' steps corresponding to fractional ratios between the numbers of vortices and triangular cells. We have performed preliminary measurements on a device containing a single weak-pinning circular ratchet channel in a Corbino geometry and observed a substantial asymmetric vortex response.
Highlights
Y O have performed preliminary measurements on a device containing a single weak-pinning circular I ratchet channel in a Corbino geometry and observed a substantial asymmetric vortex response
We study the dynamics of vortices in an asymmetric ring channel driven by an external ac current I in a Corbino setup
We study the dynamics of vortices in a circular channel formed by asymmetric triangular cells (TCs) [note that earlier this approach to form asymmetric channels in experiment was employed in a stripe geometry6]
Summary
The radius of the ring R is typically set as 6λ, where λ is the magnetic field penetration depth, the wider part of the channel (i.e., the base of TCs) w = 0.75λ, and the width of the narrow part ∆ (the neck) is typically. J where η is the dimensionless viscosity coefficient which is set here to unity Using this value of η in our calculations results in typical maximum values of vortex linear velocity v ≈ 102 m/s (for a 1μm-thick film) which is still below the Larkin-Ovchinnikov critical velocity[44,45]). We set T = 0 and apply an external driving, i.e., an ac current resulting in oscillating Lorentz force with frequency ν and amplitude I0 that acts on vortices, to study the dynamics of the system
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