Quantitative Spatio-Temporal Model-Building for Correlated Electronic Matter

• Applicants: Professorin Dr. Sabine Andergassen; Professorin Dr. Silke Bühler-Paschen; Professor Dr. Karsten Held; Professor Dr. Alessandro Toschi
• Subject Area: Theoretical Condensed Matter Physics ; Experimental Condensed Matter Physics
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 449872909

Quantum phase transitions (QPTs) represent one of the most challenging topics for theoretical and experimental investigations of correlated quantum materials because they are found in extreme parameter regimes and because of the interplay between different degrees of freedom. Our results obtained in the 1st funding period outline a clear route towards a fundamental understanding of the underlying physics. On the theoretical side, we plan to extend our investigations of quantum criticality to multi-orbital problems as well as to systems in the presence of magnetic fields. This will also allow us to study the pertinent effects of different Fermi surface geometries and of topology on quantum criticality in realistic many-body calculations that can be directly compared with experiments. Experimentally, new information will be extracted from a combination of different spectroscopies, namely inelastic neutron scattering (INS), microwave (MW) conductivity, resonant inelastic x-ray scattering (RIXS), angle-resolved photoemission spectroscopy (ARPES), and shot noise, applied to both quantum critical (QC) (e.g. Ce3Pd20Si6, YbRh2Si2) and topological (e.g. Ce3Bi4Pd3) materials. The link between both will be studied using CeRu4Sn6 where, in the 1st funding period, we identified a topological phase emerging from quantum criticality. A new focus of the 2nd funding period is the interplay between charge fluctuations and spin/orbital/lattice degrees of freedom. In the realm of QPTs, the link between the spin and charge sectors will be explicitly investigated by performing new MW-conductivity/shot-noise experiments—both sensitive to charge fluctuations—on YbRh2Si2. Theoretically, the interplay with charge fluctuations will also be considered beyond QPTs, both for unconventional superconductivity and for its possible impact on electron-phonon coupling. As a second step, we will investigate how such an interplay is modified by the inclusion of non-local interactions through dynamical mean-field theory (DMFT) and its diagrammatic extensions, such as the DΓA and the DMF2RG, in difficult but experimentally relevant parameter regimes (low-T, large interactions). This will require efficient algorithmic strategies for compressing and manipulating two-particle vertex functions such as the intermediate representation and quantic tensor trains. The corresponding methodological advances will benefit several theoretical projects of.

• DFG Programme: Research Units
• Subproject of: FOR 5249: Quantitative Spatio-Temporal Model-Building for Correlated Electronic Matter
• International Connection: Austria
• Partner Organisation: Fonds zur Förderung der wissenschaftlichen Forschung (FWF)