Open Collections

Description

All existing topological band structures can be traced back to a quantized dipole moment, or a mathematical generalization thereof. Recently, it has been shown theoretically, how the quadrupole moment of a charge distribution can be quantized. The associated phenomenology includes in-gap states on surfaces two or more dimensions lower than the bulk. Here, we report on the experimental observation of such a quadrupole state in a mechanical metamaterial made from weakly coupled oscillators in a silicon membrane. We characterize the topological in-gap “corner-states” together with the induced gapped edge modes.