Research activities

Please find more about current activities here Forschungsportal and SVT Web.

Strongly correlated electron systems

Strongly correlated electron systems are of broad interest in condensed matter physics, especially in connection with magnetic materials as well as with the high-temperature superconductivity.

Research are low-dimensional quantum spin systems: This systems show a rich variety of physical phenomena as quantum phase transitions, spin liquid behavior or exotic type of magnetic ordering. By using different analytical and numerical approaches as exact diagonalization, the 'decoupled-cell' quantum Monte-Carlo method or variational wave function calculations the ground-state, the low energy spectra, spin-spin correlations and thermodynamic properties as entropy or specific heat has been analysed. Special interest has been devoted to the question which kind of magnetic order is present in the ground-state of low-dimensional spin systems. It has been shown that strong quantum fluctuations in connection with frustration, dimensionality, coordination number and other factors influence the magnetic ordering in quantum spin systems in different ways.

Research in interacting fermion models using a diagrammatic approach: In this project I investigate the possibility of using Feynman diagramms to calculate the self-energy of an interacting fermion system. i.e. the Anderson impurity model and the Hubbard model.

Granular material

Segregation and mixing are two very interesting phenomena appearing in granular material. The interplay of different sizes, densities, shapes etc. can lead to a variety of effects.

Research of band formation and segregation in a rotating drum containing glass beads of two sizes: After mixing two types of glass beads in a rotating drum a number of bands appear which over time change in shape and thickness. Bands merge and sometimes complete segregtion occurs. The time of segregation and merging as well as the shape of the bands depends for example significantly on the speed of rotation. A large number of experiments is performed to study this behavior. Numerical investigations of the band forming behavior are carried out. The experiments include optical observation, NMR scans of the internal bead distribution as well as PIV (particle image velocimetry) measurements of the particle flow on the surface. Axial and radial segregation is observed and compared to existing models. A new model based on a simple random walk behavior is used to intepret the experimental data.

A talk about such systems had been given at the DPG-Frühjahrstagung 2006.

Axial segregation of granulate in a long horizontal rotating drum
Talk at DPG Frühjahrstagung, Dresden March 2006.

Microemulsion

A ternary mixture of oil, water and surfactant can at a given mass relation between the constituents build a so called microemulsion. This is a thermodynamically stable transparent solution where aqueous nanodroplets of 5 - 25 nm are surrounded by a surfactant layer. The droplets can be loaded with reactants and via an exchange between the droplets a chemical reaction of different reactants can take place. This can lead to a particle precipitation where very small particles of nanometer range are produced.

Research of the phase diagram of ternary and quartenary systems of oil, water, surfactant and reactants: A Metropolis Monte-Carlo method is applied on a lattice model of the system in order to study the phase behavior for a variety of different systems. The influence of a head-tail distribution of the surfactant is studied as well as the influence of reactant ions on the phase behavior.

Particle precipitation in microemulsion droplets: The exchange, reaction, nucleation and growth phenomena and their interplay on different time scales are the important processes to model the particle precipitaion in microemulsion. A kinetic Monte-Carlo method is applied to this problem. It is used to investigate the dynamics of particle precipitation as well as to indentify suitable process control parameters for an upscale approach of this technology.

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Center for Simulational Physics

Dep. of Physics and Astronomy