Research Areas in the Department Physics and Astronomy
The Department Physics and Astronomy at the University of Bochum offers a wide range of research fields.
Astronomy & Astrophysics
Hadron Physics
Solid State Physics/Material Sciences
Plasma Physics
Didactics
Interdisciplinary research and investments
Plasma Physics
Experimental physics of reactive plasmas
The main focus of the research activity is the fundamental understanding of plasma-surface interaction. For this purpose, numerous experiments are performed in reactive plasmas to identify the prevailing reactive particle fluxes as well as the resulting surface processes. In many cases, optical in-situ diagnostics in the visible and infrared as well as mass spectroscopy are used as diagnostics. The analysis is completed by a worldwide unique particle beam experiment, which allows the direct study of heterogeneous surface reactions.
Topics include the understanding of pulsed magnetized high power plasmas for the synthesis of oxides and nitrides and the plasma assisted fabrication of barriers and membranes. A large field is also the analysis of non-equilibrium processes in atmospheric pressure plasmas as they can be used for plasma catalysis and plasma assisted electrolysis.
Experimental Plasma and Atomic Physics
The research interest focuses on the physics of plasmas far from thermodynamic equilibrium. This includes questions on ohmic and shock-free heating, transport and distribution of charged and uncharged particles or propagation of electromagnetic fields as well as related aspects of atomic and molecular physics.
The application and development of new diagnostic methods is of particular importance in this context. In general, a very broad spectrum of different optical and electrical techniques is used, with a focus on laser spectroscopy. Basically, the combination of experiment, simulation and analytical modeling is used to try to achieve an understanding of the underlying physical laws and processes.
Theoretical plasma, laser and atomic physics
We deal with questions of turbulence and reconnection in plasma-physical flows. Depending on the application, the plasmas are described by kinetic or fluid dynamic models and the approach to understanding these systems is both analytical and numerical. The main tools used to investigate MHD-type systems are the racoon framework based on adaptive grid refinement and the cudaHYPE framework for parallel calculations on a cluster of graphics cards. The FlareLab experiment is accompanied by simulations with racoon and experiments on magnetic dynamos are simulated with the spectral code LaTu. Both racoon and LaTu scale linearly up to 262144 cores. Kinetic simulations are performed with the Vlasov solver DSDV.
Institute for Energy and Climate Research (Forschungszentrum Jülich)
Our focus is on energy extraction from fusion reactor combustion chambers. Extremely high thermal loads occur here, which future power plants will have to withstand in continuous load operation in order to be economical. We are researching the materials suitable for this and analyzing their plasma-wall interaction. A new research focus is the investigation of neutron-damaged fusion materials.
To this end, we also use linear plasma systems to simulate wall loading in fusion reactors. The aim is to understand the influence of the damage on the lifetime of the wall components and the incorporation of the fusion fuels deuterium and tritium in the wall material. We are developing measurement methods to characterize the plasma and the surfaces and new concepts to optimize the wall components.
Hadron Physics
Experimental Hadron Physics
Shortly after the Big Bang, the universe consisted only of the fundamental building blocks of matter. Quarks and gluons came together in a fraction of a second to form the protons and neutrons, or hadrons, as the generic term for these composite particles is called. Why we do not observe individual quarks and gluons and why the properties of hadrons are not just the sum of the properties of the building blocks is one of the main questions of hadron physics.
In order to uncover these secrets of nature, we are searching for ever new combinations of the fundamental building blocks in hadrons in experiments at large accelerator centers around the world, in order to achieve a description of the world observed today and its laws from these puzzle pieces. The state-of-the-art detector technologies we have developed in the process allow students to be trained in experimental physics at the highest technological level.
Experimental physics of hadrons and nuclei
One of the central questions of physics is the composition of matter. Especially in the field of hadrons, which includes protons and neutrons, some phenomena are still unexplained. Quantum chromodynamics (QCD), the theoretical description of the strong interaction, is in good agreement with most of the measurement results. However, neither QCD itself nor effective theories or calculations within the framework of lattice QCD are able to assign all the states found so far and to elucidate their internal structure.
Besides the improvement of the theoretical description on the part of theoretical physics, it is important, on the one hand, to search for new predicted or non-predicted states. On the other hand, in order to confirm or exclude theoretical descriptions, it is necessary to precisely measure the states that are found. Energy scan measurements allow the precise determination of the mass and width of states, while partial wave analysis enables the extraction of additional properties such as spin and parity.
In order to improve the database, I have joined forces with colleagues worldwide to set up the PANDA experiment in Darmstadt and, in parallel, to analyse the data from the BESIII experiment in Beijing.
Theoretical hadron and particle physics
We are engaged in the study of the properties of strongly interacting matter. The focus is on elucidating the internal structure and dynamics of hadrons and atomic nuclei composed of quarks and gluons - the fundamental building blocks of our matter. The particular challenge here is the strength of the interaction between quarks and gluons described by quantum chromodynamics, which leads to the failure of the usual approximation methods.
For the theoretical study of such strongly interacting hadronic systems, effective field theories are applied at the chair, in particular, which exploit certain symmetry properties of quantum chromodynamics and provide a systematic and model-independent access to hadronic observables. These analytical methods are combined with numerical techniques such as Monte Carlo simulations of hadrons placed on a lattice to analyze properties and dynamics of few-baryon systems and baryon matter.
Other research topics include quark mass dependence of hadronic observables and its implications for cosmology, electroweak processes and pion production at the nucleon and light nuclei, quantum field theory treatment of spin-3/2- fields, isospin-violating effects, hyperon-nucleon interaction and properties of hypernuclei, and charmonium physics.
Theoretical Hadron Physics
The group conducts research in various branches of theoretical high-energy physics: from quantum chromodynamics (QCD) as the theory of hadrons to models of fundamental interactions. The focus of our current research is on the study of non-perturbative effects of QCD. Due to a mysterious property of color-confinement, QCD is one of the most intriguing and dynamical theories ever. There are extremely numerous significant non-perturbative phenomena in QCD. To understand these, we use various methods of quantum field theory.
In particular, we deal with topologically non-trivial field configurations such as solitons and instantons. Currently, we are interested in the possibility that protons and neutrons represent solitons of chiral fields in QCD. Such a picture of the basic building blocks of matter around us allows us to predict a new type of baryon - the Ө+ pentaquark.
Another topic that currently fascinates us is the application of tomographic methods in hadron physics. It seems that these methods can pave the way for us to obtain three-dimensional images of hadrons.
Solid State Physics
Applied solid state physics
We are engaged in the research of semiconductors both in terms of fundamental physical phenomena and the development of innovative devices in two main areas of work:
Molecular Beam Epitaxy (MBE) for the fabrication of semiconductor heterostructures and Focused Ion Beam Implantation (FIB) for material processing.
By "band-gap-engineering", low-dimensional semiconductors of high quality with monolayer resolution are realized in AlInGaAs by means of MBE. These are two-dimensional electron layers, as they occur in every field-effect transistor, one-dimensional quantum wires or even zero-dimensional quantum dots, which will form elementary functional units of future supercomputers.
The spatial limitations lead to quantum phenomena, such as the quantum Hall effect and conductivity quantization. We measure our semiconductors optically and electrically - even at low temperatures. These serve as the basis for cutting-edge research in worldwide collaborations. Since the limits of today's lithography processes are foreseeable, we have implemented a maskless patterning technique using FIB, which does not require any chemistry at all. This technique allows to create lateral structures down to the NANOmeter range. Individual novel devices (e.g. in-plane-gate transistors) and NANO structures for the exploration of quantum phenomena become possible.
Experimental surface physics
We investigate the geometrical, electronic, vibronic and magnetic structure of nanostructures and thin film systems on semiconductor or oxide surfaces. Of particular interest are the dynamics of the formation processes of the structures, growth, adsorption and diffusion processes.
The technological objective here is to produce layers or nanostructures with specified structural, magnetic or chemical properties. The main measurement method is scanning tunneling microscopy (STM). Imaging of the samples with atomic resolution is performed in ultra-high vacuum during the formation of the nanostructures or ultrathin films. Directly during growth, the surface is observed with time resolution, allowing one to follow the growth and structure formation processes.
Chemical information about the state of the surface is obtained using high-resolution electron spectroscopy methods. Vibrational modes from molecules bound to the surface together with scanning tunneling microscopy results allow accurate characterization of the binding relationships of molecular layers on surfaces. Magnetic properties of nanostructures are studied directly during fabrication using the magneto-optical Kerr effect (MOKE). This also allows the behavior of magnetic domains to be observed on a sub-micrometer scale.
Experimental spectroscopy of condensed matter.
In solid state materials, a large number of physical processes take place within only a few nanoseconds or picoseconds. Examples are the recombination of charge carriers, magnetization dynamics or spin relaxation. The working group Spectroscopy of Condensed Matter makes such processes visible with laser spectroscopic techniques. Short pulse lasers allow the investigation of such fast phenomena with a time resolution of about 100 fs.
One focus of our experimental work is the development of materials and structures that exhibit long spin lifetimes and can be used for semiconductor spin electronics. The group also contributes to the growing field of fluctuation spectroscopy. Methods are being developed to measure and meaningfully characterize the random thermal movement of e.g. electron spins in solids or the stochastic transport of charge carriers in resistors. For this purpose, a system was developed that processes data streams of approx. 0.4 GByte/s in real time and uncovers regularities (correlations) that are hidden in the noise.
Correlation spectroscopy is used, among other things, to investigate critical dynamics at phase transitions, the quantum dynamics of mesoscopic systems and the detection of systematic sources of interference in highly sensitive measurements.
Theoretical solid state physics
The theoretical physics of condensed matter owes its richness and complexity to the fact that it deals with the quantum theory of many-particle systems. This theory describes a very large number of atoms or ions and their mutual interactions (or correlations), with phenomena that have a pure quantum mechanical origin.
In our group, we use various theoretical methods to study the electronic and magnetic properties of strongly correlated low-dimensional systems, including the unconventional high-temperature superconductivity that arises in many such systems. The peculiarity of these systems is that the electron-electron correlations are significantly enhanced by the effect of low dimensionality and the competition of spin, charge, and orbital degrees of freedom. Moreover, in such cases, it must be taken into account that the ground state of such systems can change drastically as a function of a single parameter.
In addition, our group is concerned with low-dimensional strongly correlated systems that exhibit geometric frustration of magnetic order and are responsible for many exotic quantum states of matter.
Experimental Solid State Physics
We deal with quantum materials whose properties are determined to a large extent by quantum mechanical effects. Here, for example, the interaction between electrons among themselves and between electrons and ions of the crystal lattice leads to diverse phenomena, such as magnetic order, charge density waves or superconductivity.
We produce these, often intermetallic compounds as single crystals ourselves by flux growth. We investigate their, often still unknown, structural and chemical properties with various methods. This ranges from structure determination and chemical analysis, electrical transport and thermodynamic properties to X-ray and neutron diffraction. We consider a wide temperature range of about 1 K - 400 K and high magnetic fields of up to 17 T. A special role is played by the investigation of effects caused by uniaxial pressure and strain, which we elucidate by means of high-resolution measurement of thermal expansion, elastic moduli and elastotransport.
Our goal is to understand the properties of complex materials and to learn how to control them in a targeted manner. For example, changes in composition or (anisotropic) pressure can induce new phases and achieve functional properties. In particular, we are looking for new quantum materials with exotic properties using material design methods.
Materials Science
Interdisciplinary Centre for Advanced Materials Simulation (ICAMS)
Interdisciplinary Centre for Advanced Materials Simulation (ICAMS)
Our work focuses on the theoretical characterization of the interatomic interaction and the application of models of the interatomic interaction in atomistic simulations.
The goal is to use these simulations to achieve an improved understanding of atomic properties of materials and to apply this understanding to the design of new, improved materials. Current examples are simulations for the improvement of high-temperature alloys as used in aircraft turbines, atomistic modeling of steel, in particular the embrittlement of modern ultra-high-strength steels, as well as the modeling of materials for spin electronics, thermoelectric materials for the recovery of electric energy from waste heat, etc.
The chair is embedded in the Interdisciplinary Centre for Advanced Materials Simulation (ICAMS), which deals with the modeling and simulation of materials over all length scales - from the electron to the component.
Interdisciplinary Centre for Advanced Materials Simulation (ICAMS) II
Interdisciplinary Centre for Advanced Materials Simulation (ICAMS)
Phase transformations, besides their fundamental importance for condensed matter physics, play an important role in all areas of materials physics. They determine the microstructure of materials and thus their mechanical and functional properties. The research of the chair is focused on the mesoscopic scale of heterogeneous microstructures.We develop theoretical tools to study constitutive laws of microstructure evolution at different stages. In a cross-scale approach, we combine "first-principles" calculations of phase stability with transport processes in the microstructure to infer the macroscopic and functional properties of the materials.
Institute for Materials Physics in Space - German Aerospace Center
Institute for Materials Physics in Space - German Aerospace Center
The Institute of Materials Physics in Space of the German Aerospace Center in Cologne-Porz researches properties of melts and their solidification on all length scales using theoretical and experimental methods. The aim is to predict the properties of materials from this knowledge and thus enable material design from the melt. Through comparative experiments in space and on Earth, gravity-driven phenomena such as convection, sedimentation and buoyancy become accessible to experimental determination, a prerequisite for the development of physical models to quantitatively describe solidification processes.
Scale-bridging simulation of functional composites (ICAMS).
Scale-bridging simulation of functional composites (ICAMS).
The goal of the group is the design of ferroelectric composites with superior functional properties. At the same time, we optimize several reactions with high technological importance for the extraction of electrical energy from temperature fluctuations or stress and cooling by the electrocaloric effect. Our approach is to optimize composite systems with different morphologies across scales: Superlattices, columns, and inclusions, combining the advantages of material selection, controlled inhomogeneities, domain structure, and boundary conditions at the interfaces. Our methods are scale-bridging simulations based on ab-initio parameterization with high predictive power, allowing us to fundamentally understand and design the properties of material systems.
Astronomy and astrophysics
Astronomy
The research focus of the Chair of Astronomy is extragalactic astronomy.
The goal is to better understand the process of structure formation as a constant compression of matter since the Big Bang under the influence of so-called "dark matter" by studying galaxies. The release of energy from active galactic nuclei and stars through their radiation, stellar winds and supernova explosions plays just as important a role as the interaction of outflowing gas with freshly infalling gas from intergalactic space.
These processes influence the distribution, composition and kinematics of the interstellar gas and thus the subsequent generation of stars as well as the overall appearance of galaxies. Observations with radio telescopes, such as the Very Large Array (VLA) in New Mexico (USA) or the novel Low Frequency Array (LOFAR) in Europe, are used for these investigations, as well as measurements from research satellites (e.g. Hubble or XMM/Newton telescopes of ESA) or the European large telescopes of ESO in Chile. As part of a German consortium, we are also working on a camera for the world's largest optical telescope, the Large Binocular Telescope (LBT) on Mt. Graham in Arizona. Our studies of the distribution of cosmic magnetic fields are an important link to high-energy astrophysics.
Astrophysics
Telescope time is precious and is available to the astronomer - if he is lucky - only for a few hours per year at one of the world's major observatories. Detailed long-term observations of variable objects or even spontaneous measurements are thus practically impossible. Therefore, the Chair of Astrophysics has built an observatory in the Chilean Atacama Desert at an altitude of 2,800 m, where he can carry out his own projects for about 350 nights per year at one of the best locations in the world. Three fields of work are in the foreground:
1. the formation of stars,
2. the search for extrasolar planets,
3. the structure of active galactic nuclei.
All of these areas are variable phenomena that can only be studied and understood through months of observations. Also, the physical structure of the objects is similar - albeit on different size scales. Young stars as well as black holes in galaxy centers collect matter from their surroundings and grow thereby. The matter does not flow directly, but rather via a disk of gas and dust onto the central object. In the case of young stars, planets practically always form in this disk. With five telescopes that can be remotely controlled via the Internet, students at the RUB and partners in Germany and abroad are carrying out joint projects in visible and infrared light.
Observational cosmology
One of the biggest questions in cosmology today is the cause of the accelerated expansion of the universe. Is this surprising property of the cosmos an indication of a cosmological constant? Is a new form of energy, often called dark energy, or a new, as yet unobserved particle/field responsible? Or is our theory of gravity, Einstein's general theory of relativity, incomplete? With the help of a wide variety of observational techniques, cosmologists today are trying to answer these questions.
The research activities in the Observational Cosmology group focus on exploiting the weak gravitational lensing effect, potentially the most accurate observational method for studying the accelerated expansion. Masses in the universe, such as galaxies or clusters of galaxies, affect the propagation of light and thus act similarly to optical lenses. This property leads to tiny distortions in the images of background galaxies that we take with large telescopes. The measurement of these distortions in combination with a measurement of the distance (redshift) of the background galaxies then allows to measure masses in the universe, i.e. to weigh cosmic objects.
These measurements are taken with large-format cameras on special wide-field telescopes. Since the effect is very small, large areas of the sky must be imaged in order to have enough galaxies (many millions) available for a significant measurement. Currently, the working group mainly uses data from the European projects KiDS (Kilo-Degree Survey; http://kids.strw.leidenuniv.nl/) and VIKING (VISTA Kilo-Degree Infrared Galaxy Survey). In the future, data from the LSST (Large Synoptic Survey Telescope) large telescope as well as the ESA/NASA Euclid satellite mission will be used.
Plasma Astroparticle Physics
In high-energy particle astrophysics, we are concerned with the search for the sources of cosmic rays. Although it has been known for 100 years that a continuous stream of charged particles is impacting the Earth, the mystery of its origin has still not been solved. Problems are caused by the magnetic fields that pervade the universe: They deflect the charged particles from their original path, so that the particles arriving on Earth arrive from all directions and no longer point back to their sources.
In Bochum, we deal specifically with the theoretical description of interaction and propagation of cosmic rays. In interactions of energetic particles with matter or photon fields neutral particles - neutrinos and photons - are produced. These, by being neutral, fly straight through the universe and they can therefore help to identify the origin of cosmic rays.
The cosmic rays themselves can be studied by simulating the propagation through the cosmic magnetic fields and comparing it with the observed particle distribution. The theoretically elaborated results are compared with current measurement results from large-scale astroparticle physics instruments. Leading experiments are among others the IceCube telescope at the geographic South Pole and the H.E.S.S. experiment in Namibia, in which the group is involved.
Multi-wavelength astrophysics
At the Chair of Multiwavelength Astronomy we observe sources in the Universe with light at different wavelengths from radio to gamma rays. In addition, we open new windows to the universe by doing astronomy with messengers other than light, namely with high-energy particles. Of particular interest are neutrinos: weakly interacting particles, without charge and with tiny mass. Neutrinos give us clues to the most energetic sources in the universe, capable of accelerating protons to energies 100 million times greater than the maximum particle energies in the LHC at CERN.
To better understand these sources, we are combining observations from the IceCube Neutrino Telescope at the South Pole, with optical data from the Zwicky Transient Facility (ZTF) in California, the Fermi Gamma-ray Space Telescope, and in the future, the Cherekov Telescope Array (CTA) on La Palma. In addition, we are building an optical telescope consisting of about 30 small telescopes to sample the sky in polarized light. We describe the acquired data with theoretical models to better understand the responsible physical processes in the sources.
The first source candidates we are now investigating in more detail are super-massive black holes that shred entire stars in so-called tidal disruption events or spew out relativistic jets of matter in our direction (so-called blazars).
Didactics
Have you ever wondered why you did very specific experiments on individual physics questions in school?
We explore what makes physics classes more interesting!
Our field of work comprises the planning, implementation and scientific evaluation of the success of learning processes in physics. We investigate and develop both subject-specific approaches, which are dedicated to very special topics in physics, and interdisciplinary contributions to general educational research, which are also related to physics. The focus of our investigations is on experimentation in physics education, especially on student experiments. To this end, we investigate open-ended experimentation, scientific knowledge about the properties of the scientific object in terms of possible scientific experiments, the role of measurement uncertainties in experimentation, optimal learning support in experimentation, and the development of new experiments.
The student lab as a key element
The student laboratory at our university plays a key role in this. Here we carry out the projects, take up current topics and competences of the research areas, use modern and high-quality equipment and pursue special didactic goals. This offers our research the opportunity to develop and try out new teaching concepts for the subject of physics in cooperation with schools and to test their success.
Conclusion: Our physics didactic research is more than just training physics teachers.
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