Program winter term 2015/2016

Monday, November 16, 2015, 4:15pm, Hörsaal 28 D 001

Prof. Christian Pfleiderer (TU Munich)

Condensed Matter Particle Physics in Chiral Magnets


In condensed matter physics and particle physics analogies exist
between large scale effects of local quantum degrees of freedom. An
example par excellence is the emergence, stability and decay of
skyrmions in chiral magnets and their emergent
electrodynamics. Characterised by a non-zero topological winding,
which corresponds to precisely one quantum of emergent magnetic flux,
skyrmions exhibit an extremely efficient coupling between the
conduction electrons and the magnetic properties that generates a
topological Hall signal, spin transfer torques at ultra-low current
densities and emergent electric fields. Additionally skyrmions display
an exceptional stability, which cannot be simply suppressed under
hydrostatic pressure or doping. Taken together, the unusual properties
of skyrmions in chiral magnets promise major progress in spintronics
applications, thereby opening an unexpected avenue of condensed matter
particle physics in chiral magnets.


Markus Morgenstern


Monday, November 30, 2015, 4:15pm, Hörsaal 28 D 001

Prof. Herbi Dreiner (University of Bonn)

The Bonn Physics Show


We present a novel activity in Bonn, which is both educational and an effective form of outreach. Each year, since 2002, we have a new physics show in Bonn which is developed and presented by a new class of Bonn physics students. It is thus an educational project. The show is directed at kids aged 10-99 and is thus also an outreach project. We show how combining the two aspects lead to a fruitful endeavor, which has also lead to many spin-offs, including most recently a 2 hr show on modern particle physics, with which we have travelled to Oxford, London, Padua and Trieste ... and maybe Aachen in the future. To give you a flavor of the show we include an extensive presentation of some fun experiments.

Michael Kraemer


Monday, December 14, 2015, 4:15pm, Hörsaal 28 D 001

Prof. Klaus Schulten (University of Illinois)

Title: Towards an Atomic Level Description of a Living Cell - The Photosynthetic Chromatophore of Purple Bacteria, a Milestone 


Living systems, down to their smallest, truly living components — cells — are made up of a huge number of molecules. Resolving a cell molecule-by-molecule, namely at the level of chemistry and physics, is a long-held dream, as this feat would link the life sciences with the physical sciences at the most basic level. Can such a highly resolving microscope ever be realized? The answer seems to be yes, however, this microscope will take the form of a computer. Such computational microscope is already being developed, programmed to build on biological data, as well as on chemical and physical knowledge. When can we expect to look through such a microscope and see a cell in all its molecular detail? There is a good chance it will be around the year 2022, when the first ever exascale computer is supposed to become available. This computer will be a hundred times more powerful than today's greatest machines. The optimism for soon resolving a whole cell with the computational microscope derives from a breakthrough project already achieved on present day computers, namely, the molecule-by-molecule view of a so-called cellular organelle, the photosynthetic chromatophore. This organelle is about 100 nm in size and, in volume, is about a hundredth of a very small living cell; exascale computing should enable accordingly the study of a whole, yet small, cell. The view of the chromatophore through the computational microscope, realized in full only this year, is amazing and beautiful. One sees a clockwork of linked, mostly rather elementary processes: light absorption producing optically excited chlorophyll molecules; chlorophyll excitation spreading through the entire chromatophore, inducing electron and proton transfer at certain centers; electrons being moved around by different charge carriers;protons being pumped into the chromatophores until the protons' pressure becomes high enough that they mechanically drive synthesis of molecules of ATP, a fuel that provides energy for most cellular activities. With the computational microscopy of the chromatophore, a major part of a biological cell has been resolved, for the first time in its entirety, at the level of truly basic chemistry and physics, showcasing how Angstrom-scale processes lead to 100-nm-scale overall function of solar energy harnessed to make ATP. Reaching the same detailed view for an entire living cell in 2022 promises an even better basic understanding of life in general, and human health in particular. 

Host: Paolo Carloni 


Monday, January 11, 2016, 4:15pm, Hörsaal 28 D 001

Prof. Thomas Bretz (RWTH Aachen)

Cherenkov astronomy through the ages - Silicon makes the difference


Astronomy started already thousands of years ago with the observation
of the night sky by the naked eye. Since the invention of the first
optical telescope by Galileo, knowledge of the night sky
significantly increased. But visible light is only a very small
fraction of the electromagnetic spectrum and many interesting features
reveal themselves only at other wavelengths. With modern astronomy it
became possible to observe the electromagnetic spectrum over more than
15 orders of magnitude from radio waves to TeV energies. At these very
high energies, currently the highest known emission from astrophysical
sources is detected. For this, an indirect detection method is used,
the so-called imaging air-Cherenkov technique. A recent improvement has
been the application of semi-conductor based photo sensors, so called
SiPMs replacing the classical PMTs for photon detection. They feature
an extended duty cycle and improved long-term stability which allows
for unbiased long-term monitoring of, amongst others, the brightest
known active galactic nuclei, one of the most astonishing phenomena in
the universe. Investigating their violent temporal behaviour over long
time scales promises a better understanding of their nature by
providing additional constraints on their emission processes.

This presentation will contain an introduction to the imaging-air
Cherenkov technique with an emphasize on monitoring of active galactic
nuclei and the application of semi-conductor based photo sensors.

Thomas Hebbeker


Monday, January 25, 2016, 4:15pm, Hörsaal 28 D 001

Prof. Jan Conrad (Stockholm University)

Searches for particle dark matter – in the sky and in the laboratory

The nature of particle dark matter is one of the most important questions in modern physics. World-wide efforts to find signals of dark matter particles are ongoing, mostly focusing on Weakly Interacting Massive Particles (WIMPs), which can be seen as the current paradigm. In my talk I will review the evidence for existence of particle dark matter and then focus on two exceptionally exciting venues for WIMP detection: "direct detection", the attempt to detect the very rare interaction of dark matter particles with low-background detectors in underground laboratories and "indirect detection", i.e. the attempt to detect WIMPs and learn about their nature via detecting their annihilation or decay products. In both cases, I will concentrate on the current frontier in terms of sensitivity. I will argue that during the next decade, we are on the verge of either detecting WIMPs or being forced to abandon WIMPs as the paradigm.

Julien Lesgourgues