Mechanical Analogue of a Majorana Bound State
Chun‐Wei Chen, Natalia Lera, Rajesh Chaunsali, Daniel Torrent, Jose Vicente Alvarez, Jinkyu Yang, Pablo San‐Jose, Johan Christensen
The discovery of topologically nontrivial electronic systems has opened a new age in condensed matter research. From topological insulators to topological superconductors and Weyl semimetals, it is now understood that some of the most remarkable and robust phases in electronic systems (e.g., quantum Hall or anomalous quantum Hall) are the result of topological protection. These powerful ideas have recently begun to be explored also in bosonic systems. Topologically protected acoustic, mechanical, and optical edge states have been demonstrated in a number of systems that recreate the requisite topological conditions. Such states that propagate without backscattering could find important applications in communications and energy technologies. Here, a topologically bound mechanical state, a different class of nonpropagating protected state that cannot be destroyed by local perturbations, is demonstrated. It is in particular a mechanical analogue of the well‐known Majorana bound states (MBSs) of electronic topological superconductor systems. The topological binding is implemented by creating a Kekulé distortion vortex on a 2D mechanical honeycomb superlattice that can be mapped to a magnetic flux vortex in a topological superconductor.
Topological robustness with and without particle–hole symmetry. a) Dependency of the in‐gap bound state frequencies with an increasing number of mass‐loaded bolts. b) Bound state frequency evolution under PH‐symmetry‐preserving perturbations. Note the frequency pinning of the topological mode. Insets show an enlarged view of the vortex core with numbered perturbation sites. c,d) Measured and simulated bound state map when N = 4 bolts are perturbed through mass‐loading. e–g) Simulated, mechanical bound states protected by particle–hole symmetry for N = 1, N = 5, and N = 9, respectively.