Crystallization in colloidal systems
Hard spheres or hard sphere-like colloids are model system to study crystal properties and nucleation kinetics on micrometer scales. We develop and employ very precise density functional methods (Fundamental Measure Theory) to describe these systems and study the relation of effective models such as Phase Field Crystal to this precise density functional description. This work has been supported by the DFG Priority Programm SPP 1296 Heterogeneous Nucleation (2009-2014) and currently by the DFG in a joint project with TU Vienna (Prof.Gerhard Kahl) and Uni Konstanz (Prof. Matthias Fuchs).
Lattice models are a robust workhorse in Statistical Physics to gain insights into equilibrium (e.g. phase diagrams) and nonequilibrium. Even for the lattice gas (Ising model), there are few analytical results available and most of the work has to be done numerically. We investigate models with rod-like particles (liquid crystals) using density functional theory, simulations and machine learning. This work is supported by the DFG since 2020. The machine learning aspects are supported by the local Cluster of Excellence "Machine Learning".
Cosmology in a petri dish?
Interfacially trapped, micrometer-sized colloidal particles interact via long-ranged capillary attraction which is analogous to two-dimensional screened Newtonian gravity with the capillary length λ as the screening length. Using Brownian dynamics simulations, density functional theory, and analytical perturbation theory, we study the collapse of a finitely-sized patch of colloids. Whereas the limit λ → infinity corresponds to the global collapse of a self-gravitating fluid, for intermediate λ we predict theoretically and observe in simulations a ringlike density peak at the outer rim of the disclike patch, moving as an inbound shock wave. For smaller λ the dynamics crosses over to spinodal decomposition showing a coarsening of regions of enhanced density which emerge from initial fluctuations. Experimental realizations of this crossover scenario appear to be well possible for colloids trapped at water interfaces and having a radius of around 10 micrometer.
Particles at soft interfaces
The effective interactions between trapped colloidal particles at interfaces was the research focus of the Junior Research Group 2006-2012. More information on the research can be found in the report to the DFG.
QCD phenomenology: covariant baryon models
The description of baryons as relativistic bound states of quark and diquark contains all basic properties of QCD: relativistic covariance, confinement and spontaneous breaking of chiral symmetry. In this approach, the complex and more or less unknown quark-quark correlations are replaced by the notion of diquarks as "quasi"particles. Binding with a third quark is effected by attractive quark exchange which is the minimal interaction to restore the Pauli principle of a three-quark state. A basic exposition of the model with some applications can be found in my PhD thesis, available at nucl-th/0012067 .