Topological transport control of colloidal particles

Abstract

We have studied experimentally and with computer simulations the transport of magnetic particles on top of magnetic patterns. The motion is driven by either a modulation loop of the orientation of a uniform external magnetic field or by a drift force. The application of an adiabatic modulation loop of the direction of an external magnetic field to magnetic colloids or macroscopic magnetic particles on a periodic pattern offers unprecedented control over the motion and assembly of such colloids or particles. The motion is topologically protected since only those loops that wind around special orientations of the external field induce particle transport. The set of winding numbers around the special orientations is the topological invariant that protects the motion. The colloidal or macroscopic particles are sorted into topological classes and the transport of each class can be controlled independently and simultaneously with the other topological classes. The use of non-periodic patterns facilitates the transport of identical colloidal particles independently and simultaneously. The complexity of the loop can be imprinted in either the pattern or the modulation loop. In twisted magnetic patterns high mobility peaks of non-topologically driven particles emerge at non generic magic angles, but these mo- bility peaks in contrast to topologically driven systems are very fragile and can be easily destroyed via the analogue of an Anderson transition.