MATERIALS SCIENCE AND CHEMISTRY

To unravel the complexity of the solid state, researchers from the University of Würzburg have mastered very different and complementary methods. Density functional theory in the local density approximation with added dynamical local interactions using the dynamical mean-field approximation has the merit of being material dependent since one can include the chemical constituents of materials. Spacial and temporal fluctuations are crucial to understand e.g. the Iridates, a topic that is explored with the new pseudo-fermion functional renormalization group. Another aspect of this research are realistic quantum Monte Carlo simulations of free standing graphene aiming to elucidate the role of electronic correlations.

In this project, researchers use state of the art fermion quantum Monte Carlo methods to understand emergent collective phenomena in correlated electron system. The scientists define and study theoretical models where topology emerges and leads to novel particles at quantum critical points. The flexibility of their approach also makes it possible to study the physics of magnetic moments in a metallic environment. This could, for instance, enable theoretical experiments for understanding magnetic adatoms on metallic surfaces. In this report, a succinct account of the ALF (Algorithms, Lattice, Fermions) program package, which was developed by the scientists, as well as a summary of selected research projects is provided.

Scientists of the Department of Theoretical Physics and Astrophysics of the Universität Würzburg are leveraging the computing power of high performance computing system SuperMUC of the LRZ to perform model calculations which are particularly relevant for our understanding of low energy phenomena. These model calculations are essential for computing critical phenomena and associated critical exponents which define universality classes.

In graphene, a two-dimensional material with remarkable properties, electrons move on a honeycomb lattice and exhibit the same energy-momentum dispersion relation as massless Dirac fermions. Because of the two-dimensional character, the Coulomb interaction between electrons is not screened and leads to a strongly correlated system whose collective properties can be very different from that of individual electrons. The study of such systems has a long and fruitful history, and spans research fields as distinct as high-temperature superconductors and biological systems.