Nicolas Bachelard1 Chad Ropp1 Yuan Wang1 Xiang Zhang1

1, University of California, Berkeley, Berkeley, California, United States

The propagation of waves is typically shaped through a spatial modulation of the environment. For instance, in devices achieved by repeatedly stacking layers with different properties, the propagation of waves can be forbidden over continuous frequency bandwidths, also known as bandgaps. Such structures are routinely obtained either through top-down fabrication—such as e-beam lithography—or bottom-up processes—such as self-assembly. However, these conventional materials are static and arise in thermodynamic equilibrium, which results in inherently rigid structures, thus difficult to reconfigure and very sensitive to inhomogeneity and imperfections. The observation of Nature teaches that complex materials and systems can be obtained through alternative mechanisms. Flocks of birds or schools of fish are examples of systems of high complexity that spontaneously self-organize, adapt to perturbations in their environment (e.g. predators), and collectively create synchronized motions despite important heterogeneity in their populations.

In this talk, we use Nature-inspired collective mechanisms to force the spontaneous emergence of wave devices. We report the realization of a non-equilibrium dynamic device composed of scatterers driven by a coherent field, which move along a waveguide and spontaneously organize onto a crystal-like order. Despite strong inhomogeneity in particles’ properties, the collective mechanism at play triggers the emergence of a bandgap in the transmission spectrum of the material. This work demonstrates the possibility of achieving dynamic wave materials that spontaneously organize and that are inherently robust to inhomogeneity and imperfections.