Second-order topological insulators and superconductors with an order-two crystalline symmetry

Understand

Second-order topological insulators and superconductors have a gapped excitation spectrum in bulk and along boundaries, but protected zero modes at corners of a two-dimensional crystal or protected gapless modes at hinges of a three-dimensional crystal.

• A second-order topological phase can be induced by the presence of a bulk crystalline symmetry.
• Building on Shiozaki and Sato's complete classification of bulk crystalline phases with an order-two crystalline symmetry [Phys.\ Rev.\ B {\bf 90}, 165114 (2014)], such as mirror reflection, twofold rotation, or inversion symmetry, we classify all corresponding second-order topological insulators and superconductors.
• The classification also includes antiunitary symmetries and antisymmetries.