Kolloquium der Theoretischen Physik

From Institute for Theoretical Physics II / University of Erlangen-Nuremberg

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approximately every second Tuesday from 16:15 to 17:15 in Lecture Hall F

  • 13.06.2017 Ferdinand Evers (Uni Regensburg) Correlation effects in disordered and molecular quantum wires

In the absence of interactions between the charge carriers, metallic quantum wires do not exist due to the phenomenon of Anderson localization irrespective of the carrier temperature. With the discovery of many-body localization (MBL) we have learned that the wire remains insulating even in the presence of interactions, unless the interaction strength exceeds a critical threshold. The first part of the talk will present a brief overview about the phenomenology of MBL with an emphasis on recent discoveries concerning the long-time dynamics that remain to be understood. The second part of the presentation is devoted to molecular wires in the oligoacene family, i.e. benzene, naphthalene, antracene etc.. Calculations based on the density-functional theory (DFT) predict a lowest excitation gap that is an oscillating function of the wire length. Unlike it is the case for graphene nano-ribbons, the oscillation period is not fixed by the molecular geometry and therefore can be extremely large, of the order of 10 rings and more. As we verify by DMRG-calculations, the basic predictions of DFT remain valid even in the presence of strong (1D-typical) quantum fluctuations that are not included in available DFT functionals.

  • 19.06.2017 Matthew Turner (Uni Warwick) Membranes, active matter and collective motion

I will present an overview of our recent research on the physics of membranes, active materials and collective motion, highlighting where these three themes overlap. Membranes are ubiquitous in living cells but many questions remain outstanding. These include how membrane proteins insert, how to characterise a membrane’s material properties and how membrane microphase separation might be controlled. Living membranes are generically out of equilibrium and I will discuss our work to understand the regulation of organelles, which are membrane bound machines within cells that are essential for life and are implicated in numerous diseases. Recently there has been an explosion of interest in so-called “active matter”, systems that harness energy from external fields (concentration, temperature etc) or chemical fuel (hydrogen peroxide ATP or GTP etc). They offer access to a greatly expanded class of materials that have novel properties related to their self-motility and ability to sense their surroundings and undergo active assembly (potentially with error correction). I will give examples ranging from molecular motors and active membrane pumps to collective motion in animal systems (swarms), concluding with our recent attempts to connect swarming with a principle that might underlie general AI.

  • 18.07.2017 André Eckard (MPIPKS Dresden) Time-periodically driven quantum gases: From dynamic localization to quantum Hall physics

Time periodic forcing in the form of coherent radiation is a standard tool for the coherent control of small quantum systems like single atoms. In the last years, periodic driving has more and more also been considered as a means for the coherent manipulation of many-body systems. In particular, experiments with atomic quantum gases in optical lattices subjected to driving in the lower kilohertz regime have attracted a lot of attention [see, e.g., RMP 89, 011004 (2017)]. Milestones include, i.a., the observation of dynamic localization, the coherent control of quantum phase transitions, and the realization of artificial gauge fields and topological band structures for charge-neutral atoms. It is the fact that atomic quantum gases are very well isolated from their environment and highly controllable in a time-dependent fashion that allowed for these recent advances. I will give an introduction to the concept of Floquet engineering, which underlies these experiments, present various examples like the realization of artificial magnetic fields fields and the coherent control of interactions, and discuss also challenges related to interaction-induced heating.