A fractional corner anomaly reveals higher-order topology

Citations Over TimeTop 1% of 2020 papers

Abstract

Spectral measurements of boundary-localized topological modes are commonly used to identify topological insulators. For high-order insulators, these modes appear at boundaries of higher codimension, such as the corners of a two-dimensional material. Unfortunately, this spectroscopic approach is only viable if the energies of the topological modes lie within the bulk bandgap, which is not required for many topological crystalline insulators. The key topological feature in these insulators is instead fractional charge density arising from filled bulk bands, but measurements of such charge distributions have not been accessible to date. We experimentally measure boundary-localized fractional charge density in rotationally symmetric two-dimensional metamaterials and find one-fourth and one-third fractionalization. We then introduce a topological indicator that allows for the unambiguous identification of higher-order topology, even without in-gap states, and we demonstrate the associated higher-order bulk-boundary correspondence.

Related Papers

• → Gapped symmetry preserving surface state for the electron topological insulator(2013)159 cited
• → Entanglement, fidelity, and topological entropy in a quantum phase transition to topological order(2008)107 cited
• → Symmetry-protected quantum phase transition in topological insulators(2012)1 cited
• → Gapped Boundary Phases of Topological Insulators via Weak Coupling(2016)9 cited
• → Adiabatic Preparation of Topological Order(2006)1 cited