Thomas Speck: Research

Dynamical collective behavior observed in, e.g., schools of fish and flocks of birds can often be described with simple models of so-called self-propelled particles. Even complex behavior can be reproduced by simple rules that are followed by all individuals (e.g., follow your neighbors but do not bump into them). On the microscale, both bacteria and colloidal particles have emerged as model systems to study a wealth of different phenomena such as swirling, swarming, and turbulence.
We are especially interested in the novel collective properties of colloidal Janus particles that are propelled by diffusio-phoresis or similar means, which have been realized experimentally very recently. Depending on the interplay of volume exclusion, hydrodynamic alignment of orientations, and attractive forces, several phenomena like living crystals and phase separation are observed.
For more information, please contact  Thomas Speck  and  Peter Virnau.

Most liquids (including water) can be supercooled below their melting temperature and stay in the liquid state. The reason is the presence of a free energy barrier that the system has to overcome in order to crystallize. But some liquids never crystallize and at some temperature fall out of equilibrium. They form what we call a glass, a substance that macroscopically appears as a rigid solid but which microscopically is still disordered like the liquid. A comprehensive theory describing this state of matter is still missing and is one of the major challenges in condensed matter science.
For more information, please contact  Thomas Speck.

The extraction of useable work from heat has fueled the industrial revolution of the 18th century, the scientific basis of which is provided by classical thermodynamics. Although thermodynamics can be justified by statistical arguments, it is still concerned with average values due to the vast number of degrees of freedom that comprise a macroscopic body. Quite in contrast, machines on the microscale are faced with fluctuations that are large. Our very lifes depend on such machines (e.g., proteins) to work properly. Stochastic thermodynamics is a generalization of thermodynamic notions such as work and heat to include fluctuations. In particular, the probability distributions of these quantities are not arbitrary but respect certain symmetries collectively called fluctuation theorems.
For more information, please contact  Thomas Speck.