Yearbook 2012

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Topological insulators from a chemical point of view

Max Planck Institute for Chemical Physics of Solids Felser, Claudia; Chadov, Stanislav; Müchler, Lukas; Yan, Binghai; Kübler, Jürgen; Zhang, Shou-Cheng1
Topological insulators (TIs) are a new quantum state of matter, which have attracted interest of condensed matter science. The materials are small band gap insulators with robust gapless surface states. Remarkable is that topological insulators can be predicted by ab initio theory and even understood from a chemist’s perspective. Herein, a simple recipe based on bonds, bands, symmetry, and nuclear charge will be given to motivate a systematic search for new topologically nontrivial materials. more

Novel quantum states in metals

Max Planck Institute for Chemical Physics of Solids Kirchner, Stefan; Wirth, Steffen; Pfau, Heike; Friedemann, Sven; Stockert, Oliver; Geibel, Christoph; Si, Qimao; Steglich, Frank
Quantum criticality is currently pursued across many areas of correlated matter. A particular focus is on quantum criticality in itinerant electron systems. It has been shown that the traditional theory of metals breaks down in the vicinity of a novel class of quantum critical points in metals. A better understanding of the physics of these novel quantum states yields new insights into the occurence of magnetism and superconductivity. more
The discovery of the accelerated expansion of the Universe has revolutionized the field of physical cosmology. Understanding the origin of this phenomenon is one of the most outstanding problems in physics today. This situation has led to the construction of a new generation of galaxy surveys, aimed at shedding light on this problem. The ongoing Baryon Oscillation Spectroscopic Survey (BOSS) is an example of these surveys. BOSS is probing the large-scale structure of the Universe with unprecedented precision, providing new insights on the physics behind cosmic acceleration. more

A gas cloud on its way towards the supermassive black hole at the Galactic Centre

Max Planck Institute for Extraterrestrial Physics Gillessen, Stefan; Genzel, Reinhard; Eisenhauer, Frank; Fritz, Tobias; Pfuhl, Oliver; Ott, Thomas; Schartmann, Marc; Alig, Christian; Burkert, Andreas
The black hole at the the centre of the Milky Way is – given its size – surprisingly quiet, because it is accreting only a small amount of matter currently. This may change in 2013 since a gas cloud is approaching it almost directly. In autumn 2013, the cloud will get too close to survive this fly by. The tidal forces as well as the atmosphere of the black hole will act on the gas cloud. If these interactions sufficiently slow down the gas, it can be accreted. We then may observe the „feeding“ of the black hole. more

Electroweak symmetry breaking and the search for the Higgs boson

Max Planck Institute for Physics Hollik, Wolfgang; Kortner, Sandra (für die ATLAS-Gruppe am Max-Planck-Institut für Physik)
The fundamental structures of matter and forces, according to our present knowledge, are successfully described in terms of the Standard Model of particle physics. Thereby, the Higgs boson plays a central role since it is responsible for the masses of the fundamental particles. In the search for this last bulding block of the Standard Model, the breakthrough was achieved in July 2012 by the discovery of a new fundamental particle with a mass of about 125 GeV by the experiments ATLAS and CMS  at the Large Hadron Collider (LHC) at CERN. more
Single organic molecules can not only generate single photons, but also be used as basic building blocks to manipulate light in photonic circuits. A molecule can, for example, attenuate a laser beam, act as a phase shifter or be used as an optical transistor. The principle behind these remarkable functionalities is the strong interaction of focused light with quantum emitters such as atoms, quantum dots, color centers, or molecules, whereby the latter offer exceptional opportunities. Experiments have reached a level where single molecules can communicate with each other using single photons. more

Ultrashort light propagation in hollow-core photonic crystal fibers: recent theoretical advances

Max Planck Institute for the Science of Light Biancalana, F.; Saleh, F. M.; Hölzer, P.; Chang, W.; Travers, J. C.; Joly, N. Y.; Nazarkin, A.; Russell, P. St.J.
Solid-core photonic crystal fibers have opened new possibilities in nonlinear fiber optics, due to the flexibility in engineering their dispersion properties by changing the cladding structure. However, in recent years, researchers are starting to explore the revolutionary properties of hollow-core photonic crystal fibers, which can be filled with a variety of gases to explore their molecular or atomic properties. Here we report on some recent theoretical advances in the description of intense and ultrashort light propagation in such media, leading to some beautiful and surprising physics. more
The mention of bacteria usually brings to mind the picture of a swimming cell, however, most bacteria on earth are stuck to surfaces and form complex communities – biofilms. Biofilms are responsible for myriad problems, including tooth decay and severe infections. Biofilms need food to grow and survive, but, as they expand, the diffusion of nutrients becomes too slow. Large organisms, such as humans, solve this problem by making blood vessels that rapidly carry food in our bodies.  We show that some biofilms form a similar network of channels which transport nutrients throughout the biofilm. more

Quantum electrodynamics put on a test bench

Max Planck Institute for Nuclear Physics Sturm, Sven; Blaum, Klaus; Harman, Zoltán; Keitel, Christoph H.; Köhler, Florian; Wagner, Anke; Zatorski, Jacek
The validity of the standard model of physics, even in extreme environments, can be tested by high precision measurements of values that are predicted by theory. For a single 28Si13+ ion, stored for several months in a Penning trap, the magnetic moment of the electron bound to the nucleus was measured to 11 digits precision, confirming the corresponding calculations. This constitutes to date the most stringent test of quantum electrodynamics of bound states. more

Why doesn’t iron glow as predicted?

Max Planck Institute for Nuclear Physics Bernitt, Sven; Crespo López-Urrutia, José Ramón; Harman, Zoltán
There is a large number of X-ray sources in outer space, like active galactic nuclei or our own sun. In these objects, highly charged iron ions, i.e., iron atoms with most of their electrons stripped off, play a major role. To understand the processes in space, a precise knowledge of the electronic structure of these ions is necessary. Therefore, they are prepared in the laboratory with an electron beam ion trap, and investigated with X-ray photons from synchrotrons or free-electron lasers. By this means, discrepancies between experiments and theoretical predictions are found. more
Intracellular signaling pathways reacting to outside influences decide the fate of cells. These pathways are constructed from convoluted networks of interactions amongst proteins, the properties of which define those interactions, but conversely are continuously changed by these interactions. Computer aided modeling of the dynamics of the proteins involved allows the researcher to monitor the emerging patterns in the macroscopic behavior of cells stemming from these molecular scale interactions. more
The development of novel efficient synthetic methods is a subject of great importance. Scientists of the MPI for Molecular Physiology describe new approaches for the rapid access to chemical entries. Those methods are based on mild, metal-free and environment benign processes. more
RNA polymerase II transcribes protein coding and several classes of regulatory RNAs in multicellular organisms. The C-terminal domain of the RNAPII largest subunit, RNAPII-CTD, carries conserved heptapeptide repeats that are phosphorylated at different residues by a protein kinase cascade in Arabidopsis. Recent studies start to reveal how phosphorylation of the RNAPII-CTD by TFIIH-associated protein kinases regulates growth and development via coordinated control of transcription, cell cycle and biogenesis of microRNAs and small silencing siRNAs. more
New plant diseases emerge regularly being a threat for food security. Some pathogens cause epidemics on living plants only and are called biotrophs. Comparative genomics revealed a loss of essential metabolic pathways leading to biotrophy. However, gene loss is only possible due to the ability to suppress host defense. Defense suppression and adaptability requires a large gene pool that is acquired by sexual recombination or interaction with other organisms. To get a comprehensive view on how new pathogens emerge it is important to dissect their interaction within natural habitats. more
Naturally occurring variation in wild species can be used to enhance the genetic diversity of cultivated crops and improve agronomic value. Understanding metabolic pathways and the interactions between genes, phenotype and environment is fundamental to influence crop quality. Metabolic profiling is a rapidly expanding technology for the evaluation of natural variance of metabolite content when carried out alongside nutritional and taste studies and represents a powerful approach for delineating the genetic determinants of plant chemical composition. more
In the high temperature plasmas of tokamak fusion devices, the radial transport is produced by micro-turbulence, at ion and electron Larmor radius scales. An essential element of the physical understanding of the turbulent transport is the identification of the relationship between theoretically predicted turbulent transport mechanisms and the macroscopically observed behaviors of the plasma profiles. The main results of this theoretical and experimental research performed at the Max-Planck-Institut für Plasmaphysik are presented. more
A new class of tungsten materials – tungsten fibre reinforced tungsten – is developed and investigated in the division „Plasma Edge and Wall“ of the MPI für Plasmaphysik. Tungsten fibres are combined with a tungsten matrix. Extrinsic mechanisms of energy dissipation in combination with a high ductility of the fibres lead to a strong toughness enhancement. A new method of chemical vapour infiltration for tungsten allows for the first time the fabrication of such material. The toughening mechanisms are shown by means of advanced experimental techniques such as x-ray microtomography. more
Glasses, windscreens and windows have one thing in common: They become dirty. In the field of photovoltaic we are fighting against dirt adhering to solar cells as well. Meanwhile, there are coatings on which water drops hardly adhere. However, this does not apply to organic liquids. Coatings are rather seldom repelling oils, water, soapy and protein solutions at the same time. Not only oils but red wine would roll off these surfaces without leaving stains. An almost fractal structure consisting of silica spheres unveils new opportunities in this area. more
Controlled management of thermal energy by material design is an important step in the quest of clean and renewable energies. Predictive atomistic simulations unravel the details of heat transport in nanostructures and pave the way to engineer materials at the nanoscale. Here we illustrate applications of atomistic simulation tools to the study of heat transport in silicon-based thermoelectric materials and nano-devices and in carbon nanostructures. more
Depression is a complex psychiatric disorder that is thought to develop due to a combination of genetic risk factors with exposure to aversive environments. FKBP5, a co-chaperone of stress hormone receptors, seems to be a key mediator of depression, as polymorphisms in the gene encoding FKBP5 can increase the likelihood to develop this disease. By investigating the molecular, structural, physiological and behavioral function of FKBP5 we can support the central role of this co-chaperone in stress and depression, and pave the way for the development of novel antidepressant treatment strategies. more
Words evolve not as blobs of ink on paper but in face to face interaction. The nature of language as fundamentally interactive and multimodal is shown by the study of ideophones, vivid sensory words that thrive in conversations around the world. The ways in which these Lautbilder enable precise communication about sensory knowledge has for the first time been studied in detail. It turns out that we can paint with language, and that the onomatopoeia we sometimes classify as childish might be a subset of a much richer toolkit for depiction in speech, available to us all. more
In everyday conversations, we often begin to speak before we fully determined what we are going to say and how we are going to say it. But how are speaking and thinking coordinated in time? How far do speakers think ahead? Scientists at the MPI for Psycholinguistics illustrate how analyses of the speakers' eye movements can be used to assess this question. Their studies show how the time course of sentence preparation is shaped by the content and form of the utterance that speakers produce. These findings suggest new perspectives on the relationship between thought and language. more
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