Exact Universal Characterization of Chiral-Symmetric Higher-Order Topological Phases

Abstract: Utilizing a series of Bott indices formulated through polynomials of position operators, we establish a comprehensive framework for characterizing topological zero-energy corner states in systems with chiral symmetry. Our framework covers systems with arbitrary shape, including topological phases that are not characterizable by previously proposed invariants such as multipole moments or multipole chiral numbers. A key feature of our framework is its ability to capture the real-space pattern of zero-energy corner states. We provide a rigorous analytical proof of its higher-order correspondence. To demonstrate the effectiveness of our theory, we examine several model systems with representative patterns of zero-energy corner states that previous frameworks fail to classify.