Topological Memory and Hysteresis in Ice-like Mechanical Metamaterials

In the field of "artificial spin ice," great progress has been achieved concerning the intentional manipulation of frustration incorporated within arrays of magnetic dipoles. We present a mechanical analogue of artificial spin ice built up from bistable square cells that act as simple mechanical hysterons. These unit cells deform spontaneously, so that the metamaterial contains competing local ground-state orientations, which are separated by domain walls. Tuning the stiffness of elements in the unit cell, we can control the characteristic curvature and propagation speed of these domain walls. Under textured driving from the boundaries, the system exhibits dynamic hysteresis. Moreover, when driving the system from its boundary we can also observe multiple distinct steady states. These hysteresis cycles are a novel feature of our mechanical spin-ice analogue.This mechanical metamaterial exhibits a novel memory of the topology of its initial condition, and can thus have potential application in the development of a mechanical memory storage.