Yearbook 2015

In recent years, theoretical physicists discovered that the topology of a material can lead to interesting new quantum properties. This simple concept can be applied to the electronic structure of semiconducting materials in which relativistic effects are important. In 2015, several materials like NbP, NbAs, TaP, TaAs, und MoTe₂ have been suggested by theoreticians as promissing, so-called Weyl semimetals, and have been physically characterized just a bit later. The special feature is that Weyl fermions, which occur in these materials as quasiparticles, exist in two chiralities. more

The Milky Way is a barred spiral galaxy whose central part, the rotating bulge, must have mostly formed from the Galactic disk. With new infrared data the spatial structure of the Galactic bar and bulge could be determined for the first time. This makes it possible to predict the orbits of stars in the inner Galaxy and to link these with their chemical properties. With dynamical models we investigate the present-day structure and evolutionary history of our Galaxy. more

The precise measurement of the fluctuations in the cosmic microwave background confirms the model that in the early universe a period of rapid expansion of its todays visible part has taken place. The detection of remnant gravitational waves from this period would be another milestone of experimental cosmology and would have important theoretical consequences. The theoretical department of the Max-Planck-Institut für Physik is working on building theoretical models of inflation that are based on string theory, the candidate for a theory of quantum gravity. more

Nanoscopic solid-state quantum systems are gaining significant momentum in quantum optics. Their ability to integrate into photonic nanostructures makes them promising candidates for the realization of future quantum networks. Efficient coupling of single molecules to photonic waveguide structures was recently demonstrated as an elementary building block. It should be possible to investigate the optical coupling between individual quantum systems by employing novel microresonator architectures. In the meantime, single ions in a crystal also find their application in nano-quantum optics. more

Phases of matter are usually characterized by their symmetry breaking. With the Quantum Hall Effect, a completely new class of topological phases was discovered, which cannot be characterized by symmetry breaking. These phases have highly non-local excitations that could serve as ideal building blocks for a fault-tolerant quantum computer. To understand topological phases in realistic model systems, complicated quantum-many body systems have to be solved. This can be achieved by using new efficient algorithms based on insights from the field of quantum information. more

Using the intense and ultrashort light pulses provided by the free-electron laser FLASH at DESY in Hamburg, it has been possible for the first time to observe fast dynamical processes in individual highly excited molecules as a function of time. By means of the pump-probe technique, where a molecule is excited by a first pulse and subsequently probed by a second delayed pulse, the mechanisms can be uncovered that proceed within a molecule or during its break-up [1] more

By comparing the revolution frequencies of antiprotons and negatively charged hydrogen ions in a strong magnetic field, the to date most precise mass comparison could be performed and thus the most precise direct test of the matter/antimatter symmetry with baryons, particles consisting of each three quarks. The result: the charge-to-mass ratios of protons and antiprotons are identical to the eleventh digit. more

During cell division, from each chromosome, the carriers of a cell's genome, identical copies are made in the mother cell. These are later transmitted to the two daughter cells in a process called chromosome “segregation”. Chromosome segregation requires specialized structures named kinetochores, which are established on a specialized region of each chromosome named the centromere. Kinetochores are multi-protein assemblies, and they are required to connect the chromosomes to a dynamic structure, the mitotic spindle, whose main function is to separate the replicated chromosomes. more

Plants sense microbial molecules to trigger innate immunity for protection from pathogens. However, microbes have evolved broad virulence factors that interfere with plant immune components. Therefore, immune mechanisms must be robust to cope with microbial perturbations. In addition, since too much immune response is detrimental for plant fitness, plant immune responses need to be tuned. The scientists study how plant immune signaling networks achieve the properties robustness and tunability using molecular genetics, genomics and computational modeling. more

Plants need to precisely adjust the capacity of photosynthetic electron transport to produce ATP and NADPH to their consumption by the Calvin cycle. Otherwise, an overcapacity of electron transport would lead to an increased production of reactive oxygen species and the destruction of the photosynthetic apparatus. To avoid this, the electron transport capacity is regulated by adjustments of the rate-limiting cytochrome b₆f complex. We have analyzed the contribution of complex biogenesis versus degradation to this adjustment. more

Many properties of a plasma that are not, or not in detail, experimentally accessible can be systematically investigated only in computer simulations. Many codes, however, use numerical methods that insufficiently take into account important properties of mathematical equations. This results in important phenomena not being reproduced in simulations. So-called structure-preserving integration methods could be the remedy. These combine ideas from numerics, physics, and geometry and allow more realistic simulations than classical methods. more

Following nine years of construction work and one year of technical preparations and tests on 10 December 2015 the first helium plasma was produced in the Wendelstein 7-X fusion device at the Max Planck Institute for Plasma Physics (IPP) in Greifswald. The first hydrogen plasma was to follow on 3 February 2016, this marking the start of scientific operation. Wendelstein 7-X, the world’s largest fusion device of the stellarator type, is to investigate this configuration’s suitability for use in a power plant. more

Conjugated polymers can be processed from solution; this attractive feature opens up the realization of roll-to-roll based production processes. Yet commercial success has been hindered. The MPI-P recently demonstrated that the intrinsic properties of conjugated polymers have been masked by defects and therefore have not been fully exploited so far. Our aim is to uncover and characterize these intrinsic properties and improve them further. Using polymer blends, novel properties and nanostructures are realized by controlling the phase separation between various functional polymers. more

The economic losses due to corrosion in industrialized countries can represent up to 6% of gross national product. This explains the emphasis placed on the research dealing with corrosion protection. As part of a collaboration with the Max Planck Institute for Iron Research in Düsseldorf, we have produced new coatings for an adequate corrosion protection. We studied corrosion attacks and clarified the fundamental aspects of self-healing and anti-corrosion mechanisms. more

Psychiatric disorders can affect our ability to successfully and enjoyably interact with others. The neural mechanisms of social interaction and transdiagnostic social impairments are only now beginning to be studied thanks to methodological developments. In the future, interaction-based functional neuroimaging, used by scientists at the MPI of Psychiatry, may help in the selection and refinement of treatment options for psychiatric disorders. more

The hypothesis that our native language influences our perception of the world has fascinated scientists for decades. Using neuroscientific methods, researchers at the MPI for psycholinguistics are investigating to what extent and under what conditions this hypothesis can be confirmed, by means of within- and across-language comparisons. It could be shown that the language system is automatically involved in the perception of both simple as well as more complex scenes (depicting objects or motion events). These effects occur very rapidly and thus operate almost unconsciously. more