Kontakt: Marcus Müller

Kontakt: K.-H. Rehren

In colloidal suspensions, self-assembly and self-organization processes can be easily fueled by external fields. Here we discuss recent computer simulation and theoretical results for the dynamical behavior of suspensions of ferromagnetic particles under the influence of (static and time-dependent) magnetic fields. In the first part we discuss the translational diffusion in static fields, where the particles tend to aggregate into chains. We show that the anisotropic, yet normal diffusive behavior seen in weakly coupled systems and finite fields can become anomalous both parallel and perpendicular to the field at sufficiently large coupling strengths. The second part focusses on the impact of rotating fields. Here one observes both synchronized states, where the individual particles follow the field with (on average) constant phase difference, and asynchronous states. Depending on the spatial dimension, the synchronization is accompanied by layer formation, i.e. by spatial symmetry-breaking, or by a clustering process.Our suggest that these pattern formation phenomena can be understood, at least partially, as by-products of an equilibrium phase transition.

Kontakt: A. Zippelius

We first review the theory of the spin-SAF transition in a spin-pseudospin model comprised of the frustrated quantum Ising model for pseudospins, representing the charge degrees of freedom, coupled to the Heisenberg spin chains. The model is known to undergo a phase transition with the simultaneous appearance super-antiferroelectric (SAF) pseudospin long-range order and a spin gap (spin-SAF transition). We will stress the similarities between the spin-SAF and other Peierls-type phase transitions. In particular, we will analyze the BCS ratio and show that it gets renormalized from the classical free-fermionic value. The BCS-ratio value is universal in the sense that is does not depend on the microscopic parameters of the model, and must be the same for various types of the Peierls-like transitions where the spin gap is accompanied by the structural, orbital or charge order.

Kontakt: Ansgar Kalz

Kontakt: Marcus Müller

Questions hour (14:15): Introduction to modern measurement theory and Ozawa's new formulation of the uncertainty relation

Kontakt: K.-H. Rehren

Kontakt: K.-H. Rehren

Motivated by the study of quantum quenches in integrable field theories (IFTs) and in particular the structure of the initial state after such a quench, we are led to the investigation of transformations of the Zamolodchikov-Faddeev operators that respect their algebra. After showing that, unlike in free theories, linear transformations (Bogoliubov transformations) do not satisfy this condition, we explore simple cases of infinitesimal transformations that do so and study their properties. Examples from typical IFTs like the Sinh-Gordon and Lieb-Liniger models are presented, emphasizing the possibility to study quantum quenches.

Kontakt: Stefan Kehrein

Kontakt: Marcus Müller

Kontakt: K.-H. Rehren

Kontakt: Thomas Pruschke

Kontakt: Thomas Pruschke

Kontakt: K.-H. Rehren

Kontakt: K.-H. Rehren

Kontakt: K.-H. Rehren

Kontakt: K.-H. Rehren

Kontakt: K.-H. Rehren