Graduate school QM3

We are part of the DFG Graduate school Quantum-Mechanical Materials Modeling QM3. For further information on the graduate school and upcoming events see the web page


We are part of the projects P2 and P3:

P2: Many-body instabilities in 2d materials

Several 2d materials combine strong Coulomb interactions with sizeable electron-phonon coupling, which leads to competing many-body instabilities including superconductivity, charge density waves, exciton condensates and magnetism. The realization of these phases is highly sensitive to external stimuli and atomistic structural details, which offers unprecedented possibilities for materials engineering, e.g., in the context of layered heterostructures. An appropriate theoretical description requires an atomistic theory, which accounts for dynamic correlations, retarded local and non-local interactions, and remains to be established.

We study how the two-dimensionality of materials like MoS2, functionalized graphene or NbSe2 can be exploited to control many-body instabilities (SC, CDW and magnetism) by interfacing and doping and how characteristic temperatures can be enhanced. Methods to map realistic systems onto tractable many-body Hamiltonians will be advanced (projector and Wannier function methods) and their applicability will be extended towards vertical hetero-structures. Interfaces with many-body approaches such as Eliashberg theory, dynamical mean field theory and time-dependent non-equilibrium approaches will be implemented and effects of electron plasmon coupling on many-body instabilities will be investigated.

P3: Many-body approaches to realistic quantum impurity models

Open-shell transition metal impurities in 2d materials and at oxide surfaces provide localized magnetic moments and hold promises in the context of novel solid-state information storage as well as quantum information processing. The theoretical description of these systems is, however, extremely challenging since it requires us to account for electronic correlations, spin-orbit coupling, crystal fields and hybridization effects. Combinations of ab-initio techniques with Anderson impurity models can in principle address strong electronic correlations and real material aspects on equal footing. However, realistic transition metal systems require multi-orbital Anderson impurity models, which are notoriously difficult to solve particularly in cases of low symmetry and/or strong spin-orbit coupling. Thus, the theoretical understanding of key quantities like magnetic anisotropies or spin-relaxation times remains an open problem. To change this situation, new and improved treatments for Anderson impurity models will be developed and applied.

The project will develop a theory of ground state properties, electronic excitations, magnetic anisotropies and spin-dynamics of single magnetic adatoms on /impurities in 2d materials and at oxide surfaces. To this end, we will develop approximations for realistic Anderson impurity models by mapping them on exactly solvable reference systems containing correlation / interaction terms using variational principles. New bath discretization schemes for exact diagonalization treatment of realistic Anderson impurity models shall be developed. We will implement calculations of total energies, excitation spectra and transport properties for magnetic impurities in and adsorbates on complex transition metal oxide and dichalcogenid hosts. Exact diagonalization approaches will be advanced to the treatment of optically excited systems using Green function based approaches in collaboration with P5. Applicability of AIM based approaches to describe chemical reactions at oxide surfaces via dynamical mean field theory will be explored together with P8.