Profile

In broad terms, our research focuses on electronic transport and time-dependent dynamics in mesoscopic systems, in particular topological insulators, graphene and further two-dimensional layers or hybrids of those. Such systems are often characterized by emergent pseudo-relativistic physics. Corresponding novel classes of materials have been identified, which might enable a paradigm shift for future electronics. Many of these materials have in common that their itinerant electrons exhibit (pseudo‑)relativistic behaviour: for instance, in graphene, electrons behave as massless Dirac particles, enabling studies of relativistic phenomena “in a pencil trace”. In topological insulators, the electron spin is locked to the electron momentum, since relativistic spin-orbit coupling is inherent in the relevant band structure.  Moreover, spin-orbit coupling at surfaces and in nanostructures influences electrical transport and enables novel topological phenomena. This leads to a large variety of anomalous quasiparticle dynamics, e.g. Klein tunneling and spin/anomalous Hall effect(s).

Having its roots in nuclear physics, the cross-disciplinary field of quantum chaos has swiftly developed since the 80ies, then with focus on the imprints of complex classical dynamics in corresponding quantum properties of single-particle systems. In recent years, the field has broadened towards many-body quantum chaos, vivid field in theoretical physics at the interface of statistical physics, nonlinear dynamics, many-body quantum dynamics in atomic and condensed matter and cosmology.
Many systems from all these distinctly different areas have in common that they reside at the semiclassical border between many-body classical chaos and quantum physics, in fact in a two-fold way: Far-out-of-equilibrium quantum dynamics involves high-energy excitations, associated with the usual short-wavelength limit, where wave mechanics approaches the limit of classical particles; alternatively, the thermodynamic limit of large particle numbers N can also be regarded as semiclassical, governed by an effective Planck constant 1/N.
Our research addresses fundamental questions that emerge at these complementary interfaces between the classical and quantum many-particle world. Thereby, lifting concepts from single-particle to many-body physics, semiclassical path integral techniques that are devised to bridge both realms, play a particular role in our research. The notion of “semiclassical” is meant here in the original sense of the limit of small Planck’s constant, hence clearly beyond classical physics.