German Institutes

RWTH Aachen

Physikzentrum

Institute for Theoretical Physics B

Current research of Prof. Dohm
Area of research Statistical physics
Theoretical investigation of cooperative phenomena in systems with many degrees of freedom using statistical methods
Research topics Theory of phase transitions
Statistical and dynamical properties
(Example: Susceptibility, thermal conductivity)
Interfaces (structure, fluctuations)
Field-theoretical methods
Applications

Explanation and predictions of experiments in real systems (liquids, solids) and of computer simulations as well as of planned experiments on the International Space Station ISS (NASA program Fundamental Physics in Space) or see this paper

Funding Deutsches Zentrum für Luft- und Raumfahrt (DLR)
National Aeronautics and Space Administration (NASA)
Max-Planck-Gesellschaft
Deutsche Forschungsgemeinschaft (DFG)

A detailed overview can be found in "Phase Transitions", Encyclopedia of Physics, 3rd edition, edited by R.G. Lerner and G.L. Trigg, VCH Publ., New York (2005), p. 1901.

Comparisons between our theoretical predictions and experiments under microgravity and at the superfluid transition of 4He can be found in these review articles: "Critical phenomena in microgravity: past, present, and future" by M. Barmatz et al. in Rev. Mod. Phys . 79, 1 (2007), and "Finite-size-scaling of 4He at the superfluid transition" von F.M. Gasparini et al. in Rev. Mod. Phys. 80, 1009 (2008)

Examples for Phase Transitions
liquid - solid
paramagnetic - ferromagnetic (Curie-Temperature TC)
normal conductivity - superconductivity
normal fluid - superfluid (4He)
thermal light - coherent light (laser)
diffusive transport - convective transport (Bénard-instability)
Prediction of Renormalization-Group theory

Material independent features of different systems near the critical point:
Universality and Scaling

Current research:
What is the range of validity of universality in real systems?
What is the range of validity of scaling in real systems?

Examples for Universality
Singular critical behavior of the specific heat C and the thermal conductivity lambda$ at the critical point Tc of liquids. Effects of large fluctuations require a statistical theory.
spezific heat and thermal conducivity diverge at T<sub>c</sub> C

alpha and x: "universal constants", independent of the details of the microscopic interaction.

Theoretical Methods

Theoretical description using methods of field theory (renormalization-group theory) and lattice models, methodological analogies to elementary particle physics.

  • diagrammatic perturbation theory
  • renormalization-group methods
  • stochastic dynamic models
  • analytic solution of statistical models
  • Borel resummation
  • numerical methods
  • computer simulations
Applications
  1. Real systems: superfluid 4He (ideal system for testing the theory), real fluids and magnetic systems
  2. Explanation of roundings of the singularities in (finite) computer models
  3. Predictions for high-precision experiments under microgravity conditions (NASA Program: Fundamental Physics in Space)
    • MISTE: Microgravity Scaling Theory Experiment
    • BEST: Boundary Effects Near the Superfluid Transition
    • SUE: Superfluid Universality Experiment
    • DYNAMX: Critical Dynamics in Microgravity
    • EXACT: Experiments Along Coexistence near Tricritality
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