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TT: Fachverband Tiefe Temperaturen
TT 37: Correlated Electrons: Poster
TT 37.8: Poster
Mittwoch, 19. März 2025, 15:00–18:00, P4
Quantum-Spin Impurities Coupled to a Chern Insulator: Topological Remnants — •David Alan Krüger1 and Michael Potthoff1,2 — 1University of Hamburg, Hamburg, Germany — 2The Hamburg Centre for Ultrafast Imaging, Hamburg, Germany
Treating quantum-spin impurities as classical vectors is a frequently used approximation to study the impact of local magnetic impurities on the formation of subgap bound states in insulators. Recently, the classical-spin approximation has been exploited for a "local" topological characterization of the ground-state bundle over the manifold of impurity-spin configurations, as opposed to the bundle over the Brillouin zone. This has been achieved by computing spin-Chern numbers C(S) as the corresponding topological invariants.
Here, we numerically solve a system with a single or two quantum spin-1/2 locally exchange coupled to a Chern insulator given by the QWZ model. Via Lanczos tridiagonalization, the system is mapped onto a gapped Kondo-impurity model. Local ground-state properties and local single-particle as well as magnetic excitations spectra are obtained by means of an adaptive natural-orbital configuration-interaction technique.
We study the interplay of possible remnants of the classical-spin topology, the intrinsic QWZ topology, and the finite-size Kondo effect. To this end we trace subgap excitations as a function of the local exchange-coupling strength and the mass parameter.
Keywords: spin-Chern number; gapped Kondo-impurity model; Chern insulator