Enhanced colloidal transport in twisted magnetic patterns

Abstract

Bilayers of two-dimensional materials twisted at specific angles can exhibit exceptional properties such as the occurrence of unconventional superconductivity in twisted graphene. We demonstrate here that novel phenomena in twisted materials emerges also in particle-based classical systems. We study the transport of magnetic colloidal particles driven by a drift force and located between two twisted periodic magnetic patterns with either hexagonal or square symmetry. The magnetic potential generated by patterns twisted at specific magic angles develops flat channels, which increase the mobility of the colloidal particles compared to that in single patterns. We characterize the effect of the temperature and that of the magnitude of the drift force on the colloidal mobility. The transport is more enhanced in square than in hexagonal twisted patterns. Our work extends twistronics to classical soft matter systems with potential applications to lab-on-a-chip devices.

Competition between drift and topological transport of colloidal particles in twisted magnetic patterns

“…In our colloidal system [15], the particle transport shares some similarities with electronic transport in twisted graphene. Paramagnetic colloidal particles are placed between twisted hexagonal magnetic patterns.…”

“…Paramagnetic colloids are placed between parallel magnetic bi-layers of hexagonal patterns that are shifted by half a unit-vector and twisted at a magic angle [15]. A sketch of the system is shown in figure 1(a).…”

“…where a is the magnitude of a lattice vector and R α is a two dimensional rotation matrix by an angle α around the axis normal to the pattern. At elevation z larger than the magnitude of a lattice vector (z > a), the magnetic field of a single pattern is well approximated by [15,18,20]…”

“…Here H p1 and H p2 are the magnetic fields of each of the twisted patterns. In the limit |H ext | ≫ H p , the cross-term dominates the magnetic potential which simplifies them to [15] V…”

“…Then, we rotate the patterns by angles ±α m /2 around an axis normal to them, figure 1(a). We use here α m /2 = arctan √ 3/33 ≈ 3.00 • such that the total twist is α m , which corresponds to the magic angle with the smallest drift force required to achieve macroscopic transport (when the external magnetic field is static and points normal to the patterns [15]).…”