Correlation effects in adiabatic spin dynamics

• Applicant: Professor Dr. Michael Potthoff, since 4/2024
• Subject Area: Theoretical Condensed Matter Physics
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449872909

This project explores novel physics at the crossroads between topologically nontrivial electronic structure, electron correlations and slow real-time dynamics in condensed-matter systems. Strong Coulomb interaction features the formation of local magnetic moments with a dynamics on a much longer time scale as compared to the fast femtosecond scale of conduction electrons. This time-scale separation, in the extreme adiabatic limit, is exploited to advance the formulation and the application of an effective low-energy theory, called adiabatic spin dynamics (ASD). The ASD incorporates an important topological twist: While the slow spin degrees of freedom generate the well-known Berry phase in the electronic quantum system, there is an additional feedback of Berry physics on the slow spin dynamics, which expresses itself as geometrical spin torques.Geometrical torques result from a nonzero spin-Berry curvature, which in turn is closely related to the nonlocal magnetic response of the quantum system. We analyze the largely universal curvature tensor and study its dependencies on the dimensionality, the symmetries and the topological properties of the underlying system. Considering prototypical models with topologically nontrivial electronic structure, which are relevant for experimental studies in P1, P3, P6, we explore the impact of geometrical torques on the real-time dynamics of magnetic impurities, on magnon spectra, and on thermodynamical properties. We have a clear focus on electron correlations and their twofold role, namely as a cause for the formation of local magnetic moments and for strong qualitative renormalizations of nonlocal response functions, including the spin-Berry curvature. Corresponding numerical studies require advanced diagrammatic techniques beyond dynamical mean-field theory and profit from know-how exchange with all projects of the research unit.In a close cooperation with P1 we advance the ASD approach in the parametric vicinity of a quantum-critical point in the two-dimensional Hubbard model. Effects of electron-phonon interaction in correlated Chern insulators are jointly studied with P5, by elaborating a concept of correlated adiabatic molecular dynamics, which is largely analogous to ASD but accounts for effects of geometrical forces. Together with P4 we explore the potential of generalized Chern numbers derived from the spin-, charge- or pairing-Berry curvature for finding new topological phases and classification schemes.

• DFG Programme: Research Units
• Subproject of: FOR 5249: Quantitative Spatio-Temporal Model-Building for Correlated Electronic Matter
• Co-Investigator: Professor Dr. Alexander Lichtenstein
• Ehemaliger Antragsteller: Dr. Georg Rohringer, until 3/2024