Vortex ratchet reversal: Role of interstitial vortices

Abstract

Triangular arrays of Ni nanotriangles embedded in superconducting Nb films exhibit unexpected dynamical vortex effects. Collective pinning with a vortex-lattice configuration different from the expected fundamental triangular "Abrikosov state" is found. The vortex motion, which prevails against the triangular periodic potential, is produced by channeling effects between triangles. Interstitial vortices coexisting with pinned vortices in this asymmetric potential lead to ratchet reversal, i.e., a dc output voltage that changes sign with the amplitude of an applied alternating drive current. In this landscape, ratchet reversal is always observed at all magnetic fields (all numbers of vortices) and at different temperatures. The ratchet reversal is unambiguously connected to the presence of two locations for the vortices: interstitial and above the artificial pinning sites.

Superconducting diode effect via conformal-mapped nanoholes

“…Previous experimental and theoretical studies widely showed that rectification signals in superconductors can be generated from a flux-quanta diode effect, i.e., the directional (or ratchet) motion of flux-quanta. For example, rectification was induced in superconducting thin films containing artificial nano-defects with asymmetric geometries [10][11][12][13][14][15][16][17][18][19][20][21][22][23] and in heterostructures containing asymmetrically shaped magnetic nanostructures on top of superconductors [24][25][26][27][28][29][30] . Besides introducing local asymmetries, breaking global inversion symmetries is another way to induce ratchet motion of superconducting vortices.…”

Time-dependent Ginzburg-Landau simulations of superconducting vortices in three dimensions

“…Whenever a vortex falls inside a hole, the magnetic field in it will experience abrupt jumps. Including holes in the calculations would allow to simulate effects like periodic pinning, to calculate matching fields, as well as the interaction of vortices with defects of different shapes, for example, as is usually done in the context of ratchet effects with triangular defects [11,12].…”

“…Rectification effects of the vortex lattice have attracted a lot of attention, specially in superconducting films with periodic pinning arrays, typically of triangular elements [11,12,13]. In general, nonlinear dynamics in the vortices in asymmetric potentials, under high frequency microwave or combined DC and AC (microwave) drives has recently returned into the focus of interest of the reseachers in vortex physics and applications.…”

Skyrmion Ratchet in Funnel Geometries

“…This effect has been investigated in several systems such as protein motors [2][3][4] , molecular motors [5][6][7] , colloids 8,9 , type II superconducting vortices [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] , electrons 28 , active matter [29][30][31][32] and recently in skyrmions [33][34][35][36][37][38][39] . Reversals of motion from the easy to the hard direction may occur as a function of the applied magnetic field or other variables 12,[17][18][19][40][41][42][43] due to collective interactions between particles. One of the earliest proposals of a two-dimensional (2D) periodic asymmetric potential that can induce a ratchet effect was the asymmetric funnel geometry 20,…”