Dresden 2026 – scientific programme
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MA: Fachverband Magnetismus
MA 5: Surface Magnetism and Topological Insulators (joint session MA/TT)
MA 5.6: Talk
Monday, March 9, 2026, 10:45–11:00, POT/0351
Electronic bounds in magnetic crystals — •Daniel Passos1 and Ivo Souza1,2 — 1Centro de Física de Materiales, Universidad del País Vasco, 20018 San Sebastián, Spain — 2Ikerbasque Foundation, 48013 Bilbao, Spain
A quantum system in its ground-state must display non-negative optical absorption. This simple statement forms the basis for a string of inequalities between moments of the absorptive conductivity. Through the use of sum rules, these inequalities provide bounds on quantities of physical interest. Recent discoveries include new constraints on the electronic localization length in insulators, and an upper bound on the bandgap of topological insulators. Current research focuses on finding inequalities relating ground-state properties such as the quantum metric to more directly measurable quantities.
We present a systematic study of bound relations between different electronic properties of magnetic crystals: electron density, effective mass, orbital magnetization, localization length, Chern invariant, and electric susceptibility. New results include a lower bound on the electric susceptibility of Chern insulators, and an upper bound on the sum-rule part of the orbital magnetization. In addition, bounds involving the Chern invariant are generalized from two dimensions (Chern number) to three (Chern vector). Bound relations are established for metals as well as insulators, and are illustrated for model systems. The manner in which they approach saturation in a model Chern insulator with tunable flat bands is analyzed in terms of the optical absorption spectrum.
Keywords: bounds; optical absorption; orbital magnetic moment; Chern insulators; sum rules