Fundamental laws of chiral band crossings: local constraints, global constraints, and topological phase diagrams

• Published in: arXiv.org
• Main Authors: Alpin, Kirill, Hirschmann, Moritz M, Heinsdorf, Niclas, Leonhardt, Andreas, Yau, Wan Yee, Wu, Xianxin, Schnyder, Andreas P
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 02.03.2023
• Subjects: Constraint modelling; Eigenvalues; Fermions; Phase diagrams; Physics - Materials Science; Physics - Mesoscale and Nanoscale Physics; Rotation; Topology
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2303.01477

We derive two fundamental laws of chiral band crossings: (i) a local constraint relating the Chern number to phase jumps of rotation eigenvalues; and (ii) a global constraint determining the number of chiral crossings on rotation axes. Together with the fermion doubling theorem, these laws describe all conditions that a network of chiral band crossing must satisfy. We apply the fundamental laws to prove the existence of enforced double Weyl points, nodal planes, and generic Weyl points, among others. In addition, we show that chiral space-group symmetries cannot stabilize nodal lines with finite Chern numbers. Combining the local constraint with explicit low-energy models, we determine the generic topological phase diagrams of all multi-fold crossings. Remarkably, we find a four-fold crossing with Chern number 5, which exceeds the previously conceived maximum Chern number of 4. We identify BaAsPt as a suitable material with this four-fold crossing exhibiting Chern number 5 near the Fermi energy.