Rectification of vortex motion in a circular ratchet channel

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 ω 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 ω − 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.

Magnetic flux pinning in superconductors with hyperbolic-tessellation arrays of pinning sites

“…These rings of increasing radius contain 1, 7, 21, and 56 pinning sites, correspondingly (hereafter, we ignore the central pinning site assuming that the mobility of the vortices can be examined by rotating them with respect to the center of the HT, which can be experimentally realized in a Corbino setup -see, e.g., Refs. [26][27][28] ). For the numbers of vortices considered here inside the HT (i.e., N HT v = 29, 49, and 83), the inner region contains 3, 11, and 18 unpinned vortices, correspondingly.…”

Reversible ratchet effects for vortices in conformal pinning arrays

“…Ratchet effects on asymmetric substrates have been extensively studied in colloidal systems [3][4][5] , granular matter 6,7 , and polymers 8,9 . Ratchet effects also appear in ac-driven vortices in type-II superconductors in the presence of an asymmetric substrate [10][11][12][13][14][15] , such as a quasi-one-dimensional periodic array produced by asymmetrically modulating the sample thickness 10,[16][17][18][19] , etching funnel-shaped channels for vortex flow 11,[20][21][22][23][24] , introducing asymmetry to the sample edges 25 , or adding periodic pinning arrays in which the individual pinning sites have some form of intrinsic asymmetry 13,14,[26][27][28][29][30][31][32][33][34][35] . At lower vortex densities when collective interactions between vortices are weak, the ratchet effect produces a dc flow of vortices in the easy flow direction of the asymmetric substrate; however, when collective effects are present it is possible to have reversals of the ratchet effect where for one set of parameters the vortices move in the easy direction while for another set of parameters they move in the hard direction [13][14][15][16]…”

Tunable diffusion of magnetic particles in a quasi-one-dimensional channel

“…Furthermore, q1D systems can be used as models for the study of collective phenomena in low dimensional systems, e.g, vortex matter in type-II superconductors [43,44], colloidal particles [45,46] and dusty plasmas. In addition, the mechanisms of ion transport in narrow channels [47] and DNA manipulation using magnetic particles [48,49] can be studied by modelling q1D systems.…”