de en · Collaborative Research Centers „Spin phenomena in reduced dimensions“ of the German Research Foundation, further corporate research activities ... this conference has

Preface

Switching with Coherent Spin StructuresChristian Back, Dieter Weiss, Joe Zweck

Quantum Interference of Electrons in Nano-structuresChristoph Strunk

Atomic Force Microscopy and Scanning Tunnel-ing MicroscopyFranz J. Gießibl, Jascha Repp

Semiconductor-Nanostructures (Epitaxy-Characterization-Application)Werner Wegscheider

Time-Resolved Spectroscopy of Semiconductor HeterostructuresChristian Schüller

Terahertz-Physics Sergey Ganichev

Linear and Nonlinear Optical Time-resolved SpectroscopyAlfons Penzkofer

Quantum Transport and SpintronicsMilena Grifoni, John Schliemann

Complex Quantum Systems and Spin ElectronicsKlaus Richter, Jaroslav Fabian

Quantum Chromodynamics - The Theory of Quarks und GluonsGunnar Bali, Vladimir Braun, Andreas Schäfer, Tilo Wettig

Didactics of PhysicsJosef Reisinger

Mechanical WorkshopNorbert Sommer, Johann Deinhart

Vorwort

Schalten mit kohärenten SpinstrukturenChristian Back, Dieter Weiss, Joe Zweck

Quanteninterferenz von Elektronen in Nano-strukturenChristoph Strunk

Rasterkraft- und RastertunnelmikroskopieFranz J. Gießibl, Jascha Repp

Halbleiter-Nanostrukturen (Herstellung-Charakterisierung-Anwendungen)Werner Wegscheider

Kurzzeitspektroskopie an Halbleiter-Hetero-strukturenChristian Schüller

Terahertz-Physik Sergey Ganichev

Lineare und nichtlineare zeitaufgelöste opti-sche SpektroskopieAlfons Penzkofer

Quantentransport und SpintronikMilena Grifoni, John Schliemann

Komplexe Quantensysteme und SpinelektronikKlaus Richter, Jaroslav Fabian

Quantenchromodynamik - die Theorie der Quarks und GluonenGunnar Bali, Vladimir Braun, Andreas Schäfer, Tilo Wettig

PhysikdidaktikJosef Reisinger

Mechanikwerkstatt Norbert Sommer, Johann Deinhart

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Department of Physics

In the winter term of 1970/71 the Department of Physics started lecturing at the University of Re-

gensburg. Today, 22 professors and 8 assistant pro-fessors operate at the faculty and educate approx-imately 500 physics “Diplom” students and some 350 physics-education students. In the course of a European-wide standardization, the “Diplom” degree will be converted to bachelor/master sys-tem starting with the winter term of 2007/08. New additional masters degrees („Master of Com-putational Science“, „Master of Nano Science“) are conceived, which will further strengthen the department‘s scientific profile. Particularly gifted students are able to enter an “elite-course” (ac-celerated program) with integrated doctoral work within the Élitenetzwerk Bayernánd thereby can be guided to their PhD within 6 years. The intense mentoring of the students in the various courses of study was awarded by the „Centrum für Hoch-schulentwicklung“ several times. The research in the workgroups of the Department of Physics is arranged around two main focuses, namely condensed matter with the focal point „Physics of Nanostructures/Nano-Science“, as well as theoretical particle physics, with the main topic of quantum chromodynam-ics. The consequent development of focus areas within the last ten years and the research expertise and international reputation which was acquired thereby are reflected in a multitude of coopera-tive projects by third-party funds. Apart from the Collaborative Research Centers „Spin phenomena in reduced dimensions“ of the German Research Foundation, further corporate research activities of the Department within the Research Unit „Lat-tice-Hadron-Phenomenology“, the two interdis-ciplinary Research Training Groups „Nonlinearity and Nonequilibrium in Condensed Matter“ and „Sensory Photoreceptors“, as well as our partici-pation in the Collaborative Research Center „Solid State Based Quantum Information Processing“ un-derline the Department‘s research potency. Approximately every three years, the De-partment of Physics hosts the spring meeting of the Condensed Matter Division of the German Physical Society (DPG) in Regensburg. With 4000-5000 participants, this conference has evolved to the largest physics conference within Europe. Numerous collaborations with other re-search establishments and industry form synergies and assure a continuous transfer of know-how between the University and the economy. Thus,

an implementation of new insights of fundamen-tal physical research can be enabled. Continuous-ly increasing third-party funds for the department partly testify to these fertile collaborations. Reg-ular excursions to industry and series of lectures, where physicists from the industry portray their companies and personal careers, facilitate grad-uates‘ choices for future employment and assist them in establishing initial contacts with industry.

City and University of Regensburg

The Department of Physics is one of four science faculties (mathematics, physics, biology, chem-

istry and pharmacy) at the University of Regens-burg. It was decided in 1962 by the Parliament of Bavaria that the University of Regensburg be the fourth full university in Bavaria. By the winter term of 1967/68, three faculties were able to give lec-tures. Today, 12 departments on the campus of-fer a broad spectrum of disciplines. An excellently equipped library places more than 3 million books at the students‘ and staff‘s disposal. Additionally, more than 650 ultra-modern desktop PCs in 33 computer labs are available for teaching activities and studies of the students and staff of the Uni-versity of Regensburg. Beyond specific areas of study, numer-ous cross-disciplinary features of the University help to nurture career-relevant expertise for more than 17000 undergraduates: For example, the computer center of the University provides pro-fessional courses for the procurement of skills in-volving information and communication technol-ogy. Usually, this particular option is demanded by science students. As another example, the Center for Speech and Communication facilitates not only further training in numerous foreign languages, but also participates in courses on rhetoric and moderation. Apart from the brilliant academic con-ditions of the University, the city also contributes to the attractiveness of Regensburg as a place to study. As it is sometimes known as the „north-ern-most town of Italy“, the charm of Regensburg fascinates students, as well as locals. The pictur-esque Old Town and its landmarks of the Stone Bridge and the Cathedral St. Peter were added to the UNESCO-World Heritage list in 2006. The eclectic cultural offerings and the settling of nu-merous high-tech companies favor the old Roman town as a lively place in an up-and-coming eco-nomic area.

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Preface

Introduction

The storage of data using ferromagnetic films and the reading of magnetic information via

the giant magneto-resistance effect or tunnelling magneto-resistance effect are the state-of-the-art. These effects are also envisioned for the realization of non-volatile storage media. Typical storage ele-ments require ferromagnetic contacts with physi-cal dimensions in the sub-micrometer range. The development of magnetic storage and switching elements which become smaller and faster ask for the use of fundamentally new physical pheno-mena on reduced length and time scales. With a further reduction of the physical dimensions fer-romagnetic systems with coherent spin structures like vortices or single domain structures become attractive possibilities.

Magnetic nano-disks: Vortices instead of do-mains

Magnetic Permalloy-disks (an Ni-Fe alloy) do not show complicated magnetic domains but show in-stead a coherent order of the magnetic moments depending on their size: they are arranged along concentric circles with north- and south-poles in the disk plane; only in the center the magnetic

moments point perpendicular to the disk. This ma-gnetic ground state was found in Regensburg and - independently and simultaneously - by a Japane-se group. The experimental information about the structure of the magnetic nano-vortices was ex-plored with the aid of the Lorentz-microscopy (see picture 1) and magnetic force microscopy. In order to experimentally analyze the magnetic switching of an individual nano-disk in an external magnetic field, micro-Hall magnetometry is used.

Prof. Dr. Christian BackMagnetism and Magneto-electronics

Contact:Phone: ++49 (0)941 943 2621Email: [email protected]

Switching with Coherent Spin StructuresProf. Dr. Christian Back, Prof. Dr. Dieter Weiss, Prof. Dr. Josef Zweck

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Fig. 1. Experimental verification of „in-plane“ magnetic vortices in co-balt nanostructures using Lorentz-microscopy. The disks, which are placed on a 15nm thin membrane using electron beam lithography and other nanostructuring techniques (see picture below on the left side), are irradiated with a parallel electron beam in a transmission electron microscope. In the case of a magnetic vortex, the electron beam, as shown in the right picture, is deflected by the Lorentz force such that - depending on the direction of rotation of the vortex - a bright or dark area arises in the center of the figure. This structure can again be detected in the experiment and prove the existence of ‚in-plane‘ vortices in nano-disks.

Micro-Hall magnetometry: Disks and perforated disks

The principle of micro-Hall magnetometry is shown in picture 2. Using nano-structuring the nano-disk which is to be analyzed is placed on a cross which contains a two-dimensional electron gas beyond the surface. The magnetic stray-field of the disk can be determined as a function of the magnetic field using the Hall-effect. As a result, hysteresis curves can be obtained which provide detailed in-formation about the switching of the magnetizati-on and about the motion of the vortices. The switching process was analyzed for various disk sizes and artificially introduced pin-

ning sites both experimentally and theoretically. It could be shown that the switching fields could be regulated quite precisely and that a multi-valued output signal could be achieved by bringing in se-veral defects.

Fig. 2. Principle of the micro-Hall magnetometry: The object which is to be examined (here we use a disk) is placed above the surface of a two-dimensional electron gas (2DEG) using nanostructuring on a cross-shaped-structure (schematic sketch above, image of an elec-tron microscope below on the left side). The component of the ma-gnetic stray-field which emerges from the ferromagnetic disk and is perpendicular to the 2DEG can be electrically measured via the Hall effect. The Hall voltage - measured as a function of the applied in-plane magnetic field H (below on the right side) reflects the hystere-sis curve of an individual nano-disk.

shown in figure 3: in the hysteresis loops a well-defined switching field is observed, where the par-ticle changes its direction of magnetization. In the lower image row it becomes evident that the dis-tribution of magnetization can be directly measu-red within particles of a diameter of approxima-tely 150nm. Thus, it is obvious that between the measurements indicated with c) and d) the ma-gnetization of the particle has abruptly changed by 180°.

Time-resolved Kerr-microscopy: The dynamics of a magnetic vortex state

The dynamics of the switching of simple micro-magnetic structures is of large interest. These pro-totypical structures may shed light on the possible magnetic excitations and the complex switching behavior of tiny magnetic storage cells. Within this context, the possibility to switch two stable mag-netic states via a precession of the magnetization is of particular interest. Today it is possible to ex-amine switching processes on short time scales in the laboratory. For this, the time-resolved magne-tic Kerr microscopy acts as basic principle. The ma-gneto-optic Kerr effect describes the interaction of light with magnetic material. For a polarised laser beam which is reflected on a magnetic surface, in-formation about the magnetic state can be gained by the analysis of the rotation of the polarization direction. In time-resolved Kerr-microscopy, pulsed laser beams are focused on magnetic elements. In order to analyze magnetic excitations in the pico-second regime, a magnetic field pulse which dis-turbs the equilibrium magnetization has to be syn-chronized with the probing laser pulse. Therefore, a fraction of the laser pulse is used to close an op-tical switch and which induces a current in a mic-rowave guide or micro-coil which in turn causes a magnetic field pulse at the location of the sample (see figure 4). The time resolution can be achieved in this stroboscopic experiment by the displace-ment of an optical delay line. Magnetic movies with a spatial resolution of 300nm and an image rate up to 1 picosecond (figure 4) can be obtained by the moving the delay line. The magnetic disk in figure 4 responds similarly to the membrane of a drum: by disturbing the ground state with a drum-beat, certain frequencies - i.e. notes - can generate vibration modes which correspond to the eigen-frequencies of the membrane.

Prof. Dr. Josef Zweck

Contact:Phone: ++49 (0)941 943 2590Email:[email protected]

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Micromagnetic characterization of single nanoparticles in the transmission electron microscope

Since for technological and physical reasons the examined coherent spin structures have to be smaller than 1µm, it is imperative to use methods which allow meaningful measurements at this sca-le. These measurements can be carried out using Lorentz transmission electron microscopy. There-by, on the one hand, there is the advantage of the capability of a transmission electron microsope to image small particles with a high magnification and resolution, while on the other hand, the ma-gnetic induction in the elements leads to a deflec-ting force on the electron beam of the illuminating system - the so-called Lorentz force. The strength of the Lorentz force depends on the strength and the direction of the magnetization of the sample. A simple example can be seen on the right side of figure 1: the disks shown as a cross-section pos-sess a flux closure which differs with respect to the sense of circulation. This leads to the effect that the illuminating electron beam leaves the sample

either convergent or divergent, which leads to an increase (bright) or decrease (dark) of the electron intensity. Thus, the sense of circulation of the ma-gnetization in the magnetic vortices can be easily distinguished by Lorentz microscopy. With the ap-proach of differential phase contrast and electron-beam holography, micromagnetic structures may be imaged in detail. It is even possible to determi-ne the hysteresis curves of single particles. This is

Fig. 3. In the upper half of the picture, the magnetic induction B is displayed depending on an external magnetic field. The very steep switching events, which are indicated with arrows in the right branch of the hysteresis curve, are of importance. These steps demonstrate that during the switching process of the particle no intermediate sta-tes are taken up and hence a single-domain switching is existent. In the lower half of the picture, the geometric structure of the exami-ned alloys is shown in part a). In addition, pictures, which are recor-ded via electron beam holography, of the same sample are displayed, which make obvious by the sequence of the different colors that the induction of the sample in its interior is always homogeneous, and thus of a single-domain. The frames c) and d) differ by the sequence of the colors. Here, the particle changes completely and thus causes the steep jumps in the hysteresis loops, indicated with arrows.

Prof. Dr. Dieter WeissPhysics of Micro- and Nano-structures

Contact:Phone:++49 (0)941 943 3197Email: [email protected]

The research interests of Prof. Weiss‘ team in general focus on the topic of nano-structured

semiconductors, ferromagnets, and superconduc-tors. Apart from transport investigations of low dimensional electron systems (quantum-Hall-sys-tems), the emphasis at the moment lies in the field of “spintronics”. Thereby we analyze the spin-dependent electrical transport through epitaxially grown Fe/GaAs heterostructures. A highly resolved recording of a transmission electron microscope as displayed in figure 5b shows the atom rows of GaAs and the lattice of one of our Fe/GaAs mono-crystals. The typical geometry of the assay with a Fe/GaAs boundary layer, where the resistance is analyzed depending on the direction of magneti-zation of the iron, is presented in figure 5a.

Another interesting research topic are ferromag-netic semiconductors; for example, GaMnAs. Phase coherent electric transport, in particular, which is caused by the interference of the charge carriers, is a highly topical subject. An appropriate assay with 25 switched GaMnAs wires with only ~40nm of thickness, where we look for the so-called weak localization, is shown in figure 6. Modern equip-ment for clean rooms and a laboratory for reach-ing the lowest temperatures, enabling the analysis of matter under most extreme conditions, allows such research at an international level. Our work is mainly embedded in the Collaborative Research Center „Spin phenomena in reduced dimensions“, which is sponsored by the DFG.

4. Time-resolved Kerr microscopy: magnetic disks with a vortex struc-ture are placed with lithographic methods onto a microwave guide (above left(?)). A short current pulse (black) generates a short mag-netic field pulse in the plane of the elements which excites the mag-netization (blue). With a time delay, a laser pulse records the state of the magnetization at a location on the sample (red). On top of the right side, a microscopic image of a magnetic disk in a micro-coil is shown. In this coil the field pulse is perpendicular to the surface of the sample. The sequence of images below displays the evolution of the perpendicular component of the magnetization of a cobalt disk with vortex structure after being excited by a perpendicular mag-netic field pulse.

GaAs GaAs3 nm 3 nmGaAs

epoxy

Fe

Fe

Co

ti

bi

GaAs-barrier

(a) (b)

AlGaAs

Fe Fe Fe

Abbildung 1

Abbildung 2

5µm

Fe

GaAs 3 nm

a) b)

Fig.5: (a) Schematic sample layout to measure the tunnelling mag-netoresistance of a Fe/GaAs/Fe/Co sandwich system. The resistance measured across the sandwich depends on the relative orientation of the magnetization in both iron layers. The quality of the Fe/GaAs interface is of crucial importance for such experiments. The trans-mission electron micrograph in (b) displays an epitaxial Fe/GaAs in-terface. The atom rows of GaAs as well as lattice planes in the iron layers can be seen. The transition from iron to GaAs takes place with-in an atomic layer.

GaAs GaAs3 nm 3 nmGaAs

epoxy

Fe

Fe

Co

ti

bi

GaAs-barrier

(a) (b)

AlGaAs

Fe Fe Fe

Abbildung 1

Abbildung 2

5µm

Fe

GaAs 3 nm

Fig. 6: The centre of the electron micrograph shows 25 nanowires in parallel, made of the ferromagnetic semiconductor material GaMnAs by means of high-resolution lithographic techniques. The width of an individual wire is only 40 nanometers. Transport experiments carried out on these ferromagnetic wire arrays a few thousandths degree above zero temperature exhibit quantum mechanical corrections to the resistance (weak localization). This effect allows determining the phase coherence length of the charge carriers along which the phase information of the quantum mechanical wave function is preserved.

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Modern electronics is based mainly on the clas-sical particle properties of an electron. The

other side of the electron’s behavior – its wave-like character – cannot be observed at room tem-perature because the electron wave’s coherence is disturbed by the motion of the crystal lattice. To unravel the dark side of the electrons – and maybe make later to make use of it – experiments must be performed at temperatures so low and inter-ferometers must be so small in dimension that the electron phase coherence time is sufficient to make it pass through that interferometer undis-turbed.

Fig. 1: a) Schematic of such an interferometer in which semitranspa-rent mirrors split and then rejoin an incident beam. b) Scanning electron micrograph of a GaAs/AlGaAs heterostructure in which, with an external magnetic field of 6 Tesla, two edge chan-nels (waveguides) form. The semitransparent mirrors are implemen-ted with quantum point contacts with a transmission for the one edge channel (red) adjusted to 50%, whereas there is total reflection in the other one (blue). c) Electron interferogram where the gate electrode (see b) was used to vary the retardation of the electron waves between first and se-cond channel. The measured detector voltage is a gauge for the cur-rent in the leftward edge channel.

Interferometers in Nano-Scale Semiconductor Heterostructures

Ultra-clean crystals produced by semiconductor epitaxy are particularly suitable to fabricate

electron interferometers. For the first time, our goal is to realize a two-beam interferometer –which is more difficult than it may appear due to the fact that an electron has a wavelength about ten times shorter than light. As electrons are also electrical-ly charged, and thus repel each other, their ma-nipulation requires waveguides, like optical glass fibre cables for light. A particularly elegant way to obtain such a waveguide is to use high mag-netic fields, as the Lorentz force lets the electrons run along the border of the interferometer with-out them undergoing any scattering events. This is the regime of the Quantum Hall Effect which is characterized (among other things) by the forma-tion of an electron waveguide along the borders of a two-dimensional electron gas. The number of electron states is, in this setting, inversely propor-tional to the strength of the magnetic field.

Electron Interference in Superconductors

Figure 2 shows how electron interference can oc-cur in the example of a superconducting loop.

Within such a loop, as within atoms, only certain circular currents are allowed, which can be deter-mined from discrete quantum numbers, name-ly the number of magnetic flux quanta F0=h/2e within the loop. By means of an underlying Hall bar made of an AlGaAs heterostructure, the classi-cal Hall effect allows one to determine the loop’s magnetic moment. The superconducting niobium ring measures 10 µm in diameter and has a ring

segment made of normal-conducting silver. This ‘weak link’ determines the critical current. Such a ring can be switched back and forth between two states, differing in the number of flux quanta, and can therefore be used to implement a ‘bit’ for information technology. In particular, they allow the realization of quantum bits which require the quantum-mechanical superposition of states with different quantum numbers.

a) b) c)

Fig. 2: Niobium ring (10 m diameter) with a micro bridge 500 nm long, on a Hall bar made of GaAs/AlGaAs heterostructure as a lo-cal magnetometer. The ring current can be adjusted via two sup-ply lines.

Prof. Dr. Christoph Strunk


Quantum Interference of Electrons in NanostructuresProf. Christoph Strunk

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The success in understanding the physics of sol-ids and their resulting applications (e.g., tran-

sistors, integrated circuits, computers, laser, mo-bile telephones...) can mainly be traced back to the fact, that solid states are crystalline for the most part and thus consist of a quasi-infinite periodic sequence of unit cells. Even so, the probes used for the experimental analysis of the properties of the solids are themselves made of many (of the or-der of 10^23) single atoms. Due to the increasing miniaturization of modules and also because of the interest in the electronic and mechanical prop-erties of single molecules, an experimental ap-proach to the world of single atoms is necessary. This access is achieved by atomic force microscopy and scanning tunneling microscopy. In contrast to optical or electron micros-copy, in the case of atomic force microscopy, the surface is not imaged by photons or electrons but by the frontal atom of a sharp tip, shown in the pic-ture below. In tunneling microscopy, a quantum mechanical tunneling current is measured, where-as in atomic force microscopy, the chemical bond-ing force between tip and surface is measured. For

a long time, scanning tunneling microscopy out-matched atomic force microscopy with respect to the spatial resolution. Today, this relationship has changed. The following picture (Science 305, 380, 2004) shows simultaneously recorded images using tunneling current (left column) and atom-ic force (right column) microscopy of a surface of graphite, where a tungsten tip was used. The sub-atomic symmetries within the force channel arise from the angle dependency of the chemical forc-es between the frontal atom and the surface. The tunneling current and the acting forces produce complementary information about the electronic and chemical structure of solid states at atomic scales. Modern sensors allow us to gain this infor-mation simultaneously. A field of activity of the chair is to further enhance the force sensor‘s sensitivity and to pro-duce tips who’s chemical and structural properties are engineered in a well-defined manner down to

the atomic scale. For this, microscopes with three different settings are deployed: ambient environ-ment (i.e., room temperature, air), vacuum, and vacuum at low temperatures. Up to now, the high-est spatial resolutions have been obtained in vac-uum at low temperatures. Therefore, at our chair we aim to establish these techniques even at room temperature under normal conditions. Moreover, a microscope for applications in vacuum at low temperatures is also being constructed. We have collaborations with the University of Augsburg (Prof. Dr. Jochen Mannhart) and the low-tempera-ture laboratory of IBM Research Division at the Al-maden Research Center in California (Dr. Andreas Heinrich and coworkers).

Atomic Force Microscopy and Scanning Tunneling MicroscopyProf. Dr. Franz J. Gießibl

Prof. Dr. Franz J. GießiblExperimental Nanophysics

Contact: Phone.: ++49 (0)941 943 2105Email: [email protected]

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The group was established in March 2007 by the hiring of Jascha Repp on a Lichtenberg-profes-

sorship, sponsored by the Volkswagenstiftung. The objective of the team is to study the physical and chemical properties of single ad-sorbates and adsorbate structures on insulating films on the atomic length scale. The technique of choice is low-temperature scanning tunnel-ing microscopy (STM), which in the past has been used to study metal and semiconducting surfaces with great success. Similar studies on insulating surfaces still are rare, but at the same time very promising. Most importantly, many physical and chemical properties are not only quantitatively but also qualitatively different on an insulating sur-face from those on a (semi-)conducting surface. Hence, it becomes of supreme importance to the scope of science, as it advances to the atomic length scale, to include insulating materials. New experimental possibilities which are to be exam-ined comprise (meta-)stable charging processes of individual adsorbates and STM-induced chemis-try of single molecules on insulators. Furthermore, these investigations shall open new research ave-

nues in molecular electronics, as they combine the following two elements: the electronic decoupling of an adsorbate provided by the insulator and the ability of STM to analyze the structural envi-ronment of an adsorbed molecule on the atomic length-scale and to probe the electronic proper-ties of this individual, well-characterized structure. With this, it will be possible to investigate elec-tron transport through adsorbates and adsorbate structures in a large variety of aspects, while hav-ing exact knowledge and control of the atomistic structure including the coupling to the leads. It is projected to install two scanning tunneling micro-scopes capable of working at low temperatures in ultra-high vacuum. In the first instance, one is con-structed which works at 5K. In the following years, a second is planned which allows measurements at even lower temperatures (0.3K) and in strong magnetic fields (up to about 14T). We have external collaborations with the experimental workgroup of Gerhard Meyer (IBM Zurich Research Laboratory), as well as with Mats Persson and his staff (University Liverpool) with re-spect to theoretical topics.

Prof. Dr. Jascha Repp

Prof. Dr. Jascha Repp


Structure model (in front) and measured electron distribution(background) of an individual molecule.

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Epitaxy of semiconductor heterostructures

The epitaxy of semiconductor heterostructures is one of the core competences of the chair of

Prof. Wegscheider. The main focus rests on mo-lecular beam epitaxy of III-IV semiconductor-het-erostructures and particularly of materials based on the material system GaAs-AlGaAs. Two growth chambers, connected by an ultra high vacuum transfer channel, are available for the epitaxy of these structures. While one of these chambers is designed particularly for the growth of electron or hole systems with ultra-high mobilities, the sec-ond growth chamber holds a Mn-source for the fabrication of ferromagnetic semiconductor lay-ers based on GaMnAs for spintronic applications. Since both MBE chambers are capable of growth on in-situ cleaved substrates (Cleaved Edge Over-growth, CEO), a large variety of high quality het-

erostructures for spintronic, magneto transport, and optic experiments can be grown thanks to this unique configuration:

• two-dimensional electron- and hole-systems with highest mobilities (µ > 107 cm2/Vs for electrons and µ > 106 cm2/Vs in hole systems) • electron- and hole-systems with high mobilities on cleaved surfaces • quantum wires and quantum dots grown by CEO • ferromagnetic GaMnAs layers together with high mobility electron systems and on cleaved surfaces• devices for spintronic applications

Research on semiconductor nanostructures grown by epitaxy

In our group, installations for measurements of magnetotransport in fields up to 16T and at tem-

peratures as low as 350mK are available, as well as for micro-photoluminescence experiments with a spatial resolution of less than 0.9µm. Apart from the efficient identification of relevant properties - e.g., charge carrier density and mobility of charge carrier systems with ultra-high mobilities or thick-

ness and quality of layers with quantum films, quantum wires or quantum dots for optical ex-periments - of the fabricated semiconductor het-erostructures, examination of more sophisticated physical problems is possible. Thus, at the moment the question of spin properties in reduced dimen-sions of these materials is up-to-date, as well as their applications in potential devices.Besides the research activities in our group, many layered structures of high quality are produced for the analysis of other national and internation-al groups, mainly sponsored by the embedding in Research Associations (SFB 631, SFB 689, BMBF-‘NanoQuit‘, DFG SPP ‚Spintronics‘).

Prof. Dr. Werner WegscheiderSemiconductor-Nanostruc-tures


Detail of the MBE labora-tory: Samples prepared for further processing.

Raughness of a epitaxially grown Quantumwell, mea-sured by confocal micros-copy and spectroscopy. The colour represents the energy of the photolumi-nescence signal of a Quan-tumwell at different posi-tions on the sample. The large variations observed in the left picture are due to thickness fluctuations in the Quantumwell. An ad-ditional annealing step dur-ing sample growth reduces these fluctuations drastical-ly (right picture).

Details of the MBE laboratory:Top: One of both chambers for epitaxy.Down: Inside the UHV transfer channel.

Semiconductor-Nanostructures (Epitaxy-Characterization-Application)Prof. Dr. Werner Wegscheider

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The workgroup of Christian Schüller, which was established in October 2004, investigates the

spin and charge-carrier dynamics in semiconduc-tor heterostructures, which are manufactured in the MBE of the chair Wegscheider. One main focus of research is the spin dynamics in high-mobility 2D hole systems, which is supported by the Pri-ority Program „Semiconductor Spintronics“ of the DFG. Furthermore, heterostructures of non-mag-netic and ferromagnetic III-IV semiconductors are analyzed within the scope of the Collaborative Re-search Centre 689 „Spin phenomena in reduced dimensions“. Therefore, a 3He Split-Coil cryostat (base temperature 500 mK, magnetic field 11.5 T, optical access) and a microscope cryostat are avail-able. The applied methods of measurement are time-resolved pump-probe spectroscopy, time-re-solved Faraday rotation, time-, spatial- and polar-ization-resolved photoluminescence with a streak-camera system, as well as Kerr-magnetometry. A pulsed Titanium-Sapphire laser with a pulse length of 500 fs is used for excitation.

In the Raman laboratory, which is cur-rently set up, electronic excitations in semiconduc-tor heterostructures are analyzed using resonant Raman scattering. In addition, the installation of a system for time-resolved Raman spectroscopy is planned. For this laboratory, a microscope cryostat with a magnet system, a triple Raman spectrome-ter, as well as a CW and ps Titanium-Sapphire laser systems, are going to be procured.

Fig. 1: time- and polariza-tion-resolved photolumi-nescence measurement on a semiconductor hetero-structure taken with the streak camera. The sample consists of two nonmagnet-ic quantum wells (QW) and a ferromagnetic Ga(Mn)As top layer. In the measure-ment performed at 4 Kel-vin with an applied in-plane magnetic field of 6 Tesla, the decay of the PL intensi-ty oscillations clearly shows that the spin lifetime in the upper QW, close to the Ga(Mn)As layer, is increased by a factor of 3.

Fig. 2: A photograph taken in the ultrafast spectrosco-py lab. In the foreground, the 3He cryostat is visible, the spectrometer is on theright-hand side of the op-tical table. A green solid-state laser is used to excite a sample for photolumines-cence experiments..

Prof. Dr. Christian Schüller

Contact:Phone: ++49 (0)941 943 2078Email:[email protected]

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Time-Resolved Spectroscopy of Semiconductor HeterostructuresProf. Dr. Christian Schüller

The research activity in the workgroup of Prof. Ganichev is focused on the terahertz frequency

range, which may loosely be defined by the limit-ing frequencies 0.2 THz and 30 THz correspond-ing to wavelengths extending from 1500 µm to 10 µm. This field is one of the frontiers of phys-ics, holding great promise for progress in diverse fields like solid state physics, astrophysics, plasma physics and others as well as having a wide ap-plication potential in medicine, environment mon-itoring, spectroscopy of different kinds of mate-rials, including explosives e.g. for inspections of content of containers, for point-to-point commu-nication, etc. The leading topics in the workgroup of Prof. Ganichev are fundamentals of spintronics, generation and detection as well as the modifica-tion of terahertz radiation. The analysis of tunnel-ing phenomena and non-linear optical effects in solids, the development of new methods for ma-terials research, imaging techniques for medicine and investigation of the interaction of terahertz radiation with biological substances are also some of the group’s research interests. The terahertz laboratories of the team of Prof. Ganichev allow experiments in a spectral range which stretches from the near- to far-infra-red over three decades, including the whole tera-hertz range. A total of eight lasers and spectro-scopic systems provides from small to the world‘s highest intensities which are used in the spec-troscopy of solids. In the terahertz range high-ra-diation intensity is of particular interest because it gives rise to a variety of nonlinear phenomena whose characteristic features are basically differ-

ent from the corresponding effects at microwave frequencies as well as in the range of visible radi-ation. This is due to the fact that in the electron-photon interaction the transition from semiclassi-cal physics with a classical field amplitude to the fully quantized limit with photons occurs at tera-hertz frequencies. The possibility to vary both the

frequency and the intensity of high-power radia-tion sources in a wide range yields the unique op-portunity to study the same physical phenomenon in both limits. By that one can achieve that either the discrete properties of light quanta or the wave character of the radiation field dominates the radi-ation-matter interaction. In general, the research with terahertz excitation is supposed to determine the limits of the actual high-frequency electronics and uncover new physical phenomena which en-able future electronics at terahertz frequencies.

Several projects aimed to different topics are car-ried out in this group. In particular, those being advanced in several research teams throughout Germany are:a. „Spin phenomena in reduced dimensions“, Col-laborative Research Centre 689/1 of the DFG (Ger-man Research Foundation)b. „Non-linearity and non-equilibrium in con-densed matter“, Research Training Group GK638 of the DFG

Besides the research within the department in co-operation with the groups of D. Weiss, W. Weg-scheider, C. Schüller, U. Rößler, and C. Back, there are intensive international collaborations with the A.F. Ioffe Institute, St. Petersburg, Russia; Walter Schottky Institut, Garching, Germany; Universität Linz, Austria; Herriot Watt University, Edinburgh, UK; Universities of Surrey and Bath, UK; University of Berkeley and University of Purdue, USA; Trinity College, Dublin, Ireland; Free Electron Laser FELIX, Netherlands; Technion, Haifa, Israel; Elektrotechni-cal Institute, Prag, Czech Republic; Tohoku Univer-sity, Japan; Hong Kong University, China, and sev-eral other institutions.

Prof. Dr. Sergey D. Ganichev


One of the THz labs

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Terahertz-Physics Prof. Dr. Sergey D. Ganichev

Large laboratory hall

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Aim of the chair is to investigate properties of complex quantum systems with main focus on

charge and spin transport as well as on the effects of the interaction of the relevant quantum system with its surroundings. Specifically, we investigate transport through interacting molecules and car-bon nanotubes, spin-orbit effects in semiconduc-tors, properties of dilute magnetic semiconduc-tors, relaxation and dephasing in qubit systems, quantum information theory or directed transport in ratchet structures. The chair is presently supported by the Deutsche Forschungsgemeinschaft under the programs SFB 631 “Solid state quantum information process-ing”, SFB 689 “Spin-phenomena in reduced di-mension”, GRK638 “Nonlinearity and non-equi-librium in condensed matter physics”, SPP 1243 “Quantum transport at the molecular scale”.

Workgroup Grifoni

Focus of the workgroup is the investigation of physical properties of many-body systems,

where the many-body problem arises either due to the presence of electron-electron interactions, or to the interaction of the relevant quantum sys-tem with the many-degrees of freedom of an envi-ronment, or both together. Specifically, spin and charge transport in inter-acting nano and mesoscopic systems, as organic single molecules or carbon nanotubes, is investi-gated. Aim of our research is in particular to inves-tigate how the underlying microscopic structure of the system is to be observed in the current-voltage characteristics, and hence also be exper-imentally measured. For example, due to the lin-ear character of the electronic bands of metallic single-walled nanotubes (SWNT) at low energies, such systems exhibit non-Fermi liquid properties which might lead to a power-law behaviour of var-ious transport quantities and spin-charge separa-tion. Moreover, the presence of two Fermi-points yields a characteristic four-electron periodicity of the current vs. gate voltage (see Figure 1) in SWNT quantum dots. Bosonic reservoirs are instead considered e.g. when analyzing dissipation and dephasing ef-fects on the dynamics of quantum particles mov-ing in a given single particle potential. This situ-ation mimics e.g. the problem of evaluating the dephasing times in (realistic) flux qubits devices,

in spin-chains or for particles moving in period-ic structures. Recent focus of the group is e.g. in calculating the dissipative dynamics of a two-level particle in the presence of non trivial environments (see Figure 2.) as e.g. the one seen by a flux qubit due to the presence of the SQUID detector, and to develop dynamical equations valid over the whole

regime of temperatures and coupling strengths to the bath. The possibility of directed spin-transport in dissipative periodic structures due to the pres-ence of spin-orbit coupling is also a present topic of research.

Prof. Dr. Milena GrifoniQuantum Transport and Dissipation


Prof. Dr. John Schliemann


Workgroup Schliemann

Research of the workgroup chiefly includes the-oretical investigations on the following topics

- Spintronics, spin dynamics in semiconductors - Ferromagnetic semiconductors - Quantum computing in solid state systems - Quantum information theory - Bilayer quantum Hall systems

The field of spin electronics, or for short spintronics, is one of the most active and rapidly growing areas of today’s solid state research, both from an experimental and a theoretical point of view. It comprises the whole plethora of efforts and proposals towards using the spin of electrons instead of, or in combination with, its charge for information processing, or, even more ambitious, quantum information processing. Therefore spin-tronics deals with the hardware of possible future computer systems. From a materials aspect, it has close connections to field of ferromagnetic semi-conductors with manganese-doped gallium arse-nide being a paradigmatic example. Here the goal is to combine the magnetic properties of metals with the transport properties of semiconductors in one and the same material at room temperature. Another active field of semiconductor research are bilayer quantum Hall systems which have also been investigated in this group. Moreover, the field of spintronics is also related to research in quantum information processing is solid state sys-tems. Finally, this group is also actively working on more abstract questions of quantum information theory, touching issues in the realm of mathemati-cal physics.

Fig. 2: The environment induces nonlocal in time correlations between tunnelling transitions of a two-level particle occurring at times t1, t2, ... (Nesi, Paladino, Thorwart, Grifoni (2007))

Fig. 1: Conductance as a function of gate voltage in a SWNT wea-kly contacted to leads. Resonance peaks are found whenever the electrochemical potential allignes the ground state energies of two neighbouring charge states. The characteristic shell structure of SWNTs causes the fourfold periodicity (from Mayrhofer and Grifoni, PRB 74 R121403 (2006)).

Ferromagnetic Semiconductors

Solid state quantum information processing

Quantum Transport and SpintronicsProf. Dr. Milena Grifoni, Prof. Dr. John Schliemann

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Aim of the chair is to investigate properties of complex quantum systems with main focus on

charge and spin transport as well as on the effects of the interaction of the relevant quantum system with its surroundings. Specifically, we investigate transport through interacting molecules and car-bon nanotubes, spin-orbit effects in semiconduc-tors, properties of dilute magnetic semiconduc-tors, relaxation and dephasing in qubit systems, quantum information theory or directed transport in ratchet structures. The chair is presently supported by the Deutsche Forschungsgemeinschaft under the programs SFB 631 “Solid state quantum information process-ing”, SFB 689 “Spin-phenomena in reduced di-mension”, GRK638 “Nonlinearity and non-equi-librium in condensed matter physics”, SPP 1243 “Quantum transport at the molecular scale”.

Workgroup Grifoni

Focus of the workgroup is the investigation of physical properties of many-body systems,

where the many-body problem arises either due to the presence of electron-electron interactions, or to the interaction of the relevant quantum sys-tem with the many-degrees of freedom of an envi-ronment, or both together. Specifically, spin and charge transport in inter-acting nano and mesoscopic systems, as organic single molecules or carbon nanotubes, is investi-gated. Aim of our research is in particular to inves-tigate how the underlying microscopic structure of the system is to be observed in the current-voltage characteristics, and hence also be exper-imentally measured. For example, due to the lin-ear character of the electronic bands of metallic single-walled nanotubes (SWNT) at low energies, such systems exhibit non-Fermi liquid properties which might lead to a power-law behaviour of var-ious transport quantities and spin-charge separa-tion. Moreover, the presence of two Fermi-points yields a characteristic four-electron periodicity of the current vs. gate voltage (see Figure 1) in SWNT quantum dots. Bosonic reservoirs are instead considered e.g. when analyzing dissipation and dephasing ef-fects on the dynamics of quantum particles mov-ing in a given single particle potential. This situ-ation mimics e.g. the problem of evaluating the dephasing times in (realistic) flux qubits devices,

in spin-chains or for particles moving in period-ic structures. Recent focus of the group is e.g. in calculating the dissipative dynamics of a two-level particle in the presence of non trivial environments (see Figure 2.) as e.g. the one seen by a flux qubit due to the presence of the SQUID detector, and to develop dynamical equations valid over the whole

regime of temperatures and coupling strengths to the bath. The possibility of directed spin-transport in dissipative periodic structures due to the pres-ence of spin-orbit coupling is also a present topic of research.

Prof. Dr. Milena GrifoniQuantum Transport and Dissipation


Prof. Dr. John Schliemann


Workgroup Schliemann

Research of the workgroup chiefly includes the-oretical investigations on the following topics

- Spintronics, spin dynamics in semiconductors - Ferromagnetic semiconductors - Quantum computing in solid state systems - Quantum information theory - Bilayer quantum Hall systems

The field of spin electronics, or for short spintronics, is one of the most active and rapidly growing areas of today’s solid state research, both from an experimental and a theoretical point of view. It comprises the whole plethora of efforts and proposals towards using the spin of electrons instead of, or in combination with, its charge for information processing, or, even more ambitious, quantum information processing. Therefore spin-tronics deals with the hardware of possible future computer systems. From a materials aspect, it has close connections to field of ferromagnetic semi-conductors with manganese-doped gallium arse-nide being a paradigmatic example. Here the goal is to combine the magnetic properties of metals with the transport properties of semiconductors in one and the same material at room temperature. Another active field of semiconductor research are bilayer quantum Hall systems which have also been investigated in this group. Moreover, the field of spintronics is also related to research in quantum information processing is solid state sys-tems. Finally, this group is also actively working on more abstract questions of quantum information theory, touching issues in the realm of mathemati-cal physics.

Fig. 2: The environment induces nonlocal in time correlations between tunnelling transitions of a two-level particle occurring at times t1, t2, ... (Nesi, Paladino, Thorwart, Grifoni (2007))

Fig. 1: Conductance as a function of gate voltage in a SWNT wea-kly contacted to leads. Resonance peaks are found whenever the electrochemical potential allignes the ground state energies of two neighbouring charge states. The characteristic shell structure of SWNTs causes the fourfold periodicity (from Mayrhofer and Grifoni, PRB 74 R121403 (2006)).

Ferromagnetic Semiconductors

Solid state quantum information processing

Quantum Transport and SpintronicsProf. Dr. Milena Grifoni, Prof. Dr. John Schliemann

Prof. Dr. Klaus RichterTheoretical Physics


Complex Quantum Systems and Spin Electronics Prof. Dr. Klaus Richter, Prof. Dr. Jaroslav Fabian

The main research focus of our groups is in the area condensed matter theory. More specifical-

ly, the work ranges from molecular electronics to spin electronics, from mesoscopic physics of elec-tronic and atomic systems to the topic of chaos in quantum systems. Transport phenomena (con-ductance in nanostructures and single molecules, spin-dependent transport, propagation of cold atom gases) are in the foreground and provide the mutual theme and methodical framework. Quan-tum coherence together with the influences of re-duced dimensions of nanosystems, as well as with disorder-, spin- and interaction-effects lead to a multitude of novel quantum phenomena.

Working group Klaus Richter

Charge transport through complex quantum systems of mesoscopic to molecular scales – in

particular, ballistic nanostructures (see Figure 1), quantum dots and single molecules – is the focus of our research. In the context of semiconductor-based spin-electronics, we are interested in spin effects in coherent charge transport under the influence of inhomogeneous magnetic fields or spin-orbit interactions. The coupling of orbital and spin de-grees of freedom, combined with effects due to the finite system geometry, leads to novel effects in spin dynamics and relaxation: recently, we have demonstrated that the combination of a superlat-tice and spin-orbit interactions in mesoscopic con-ductors with AC voltage provides spin-polarized currents, thus acting as a ”spin ratchet”. We also investigate the charge transport through single-molecule bridges between macro-scopic conductors to learn how genuine molecular properties, such as vibrational degrees of freedom of the molecules, as well as interaction effects (Coulomb blockade), modify the conductance of molecular bridges. Our quantum transport calcu-lations are carried out mostly in the context of the Landauer and Keldysh formalism with the aid of Green function methods. At the gateway between atomic and me-soscopic physics we investigate the propagation of ultracold atoms and Bose-Einstein condensates through artificial atomic wave guides and cavities (“atom on a chip”). Nonlinearities in the equations describing the condensate dynamics lead to spe-cific effects; for example, the “atom blockade” in the transmission through double-barriers, which was discovered by our group (see Figure 2). Mesoscopic systems in the intermediate regime between micro- and macrophysics are ide-al candidates for studying the interplay between classical and quantum mechanics; in particular, signatures of chaotic classical dynamics in the cor-responding quantum system. By developing ad-vanced semiclassical methods we managed to de-tect subtle correlations in classical dynamics (see Figure 3) which proved to be of key importance for the explanation of statistical properties of energy levels, as well as allow for a consistent formula-tion of a semiclassical theory of ballistic quantum transport.

Fig. 1: Computed electron density in a quantum dot

Fig. 2: Bose-Einstein condensate in a wave guide with double barrier

Fig. 3: Pair of ćorrelated´ classical trajectories, where the right loop is traversed in the same, the left loop is traversed in the opposite di-rection.

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Prof. Dr. Jaroslav Fabian

Contact:Phone.: ++49 (0)941 943 2031Email: [email protected]

Working group Jaroslav Fabian

The main focus of our group is “spintronics”, an emerging branch of electronics in which the

electron spin degree of freedom is employed, in addition to the electron charge, to manipulate and store information. We deal with various aspects, both fundamental and applied, of spintronics.

On the fundamental side, we study spin-polarized transport and spin-polarized tunneling in metals and semiconductors, spin relaxation and spin dynamics in bulk systems, as well as in quan-tum dots, and coherent transport of spin-entan-gled states in systems such as quantum dots.In quantum dots, we have proposed spin-to-charge conversion based on spin-dependent inter-dot tunneling, or a way to produce or detect spin entanglement with adiabatic passage schemes – the so-called entanglement distillation by adiabat-ic passage (EDAP). Finally, we have looked at spin relaxation in single and coupled lateral quantum dots and discovered geometries for robust spin-based quantum information processing. Our plans

also include ab initio and Monte Carlo investiga-tions of ferromagnetism of semiconductor quan-tum wells and interface systems, quantum trans-port through magnetic structures. On the applied side, we develop and sim-ulate novel schemes for spintronic devices, such as magnetic diodes, magnetic bipolar transistors, magnetic resonant tunneling diodes, m-MOBILEs, digital magnetoresistance, etc. We have discov-ered a new magnetoresistance principle – what we call digital magnetoresistance (DMR) – in which re-sistance of a device changes digitally (by a jump) if an applied magnetic field changes (continuously) through a certain threshold value.

Research funding and collaborations

The main part of the scientific staff is support-ed by the DFG in the framework of the Col-

laborative Research Centers “Spin phenomena in reduced dimensions” and “Solid state based quan-tum information processing”, the Research Train-ing Groups “Nonlinearity and nonequilibrium in condensed matter”, as well as through partici-pating in the priority programs “Quantum trans-port at the molecular scale” and “Semiconductor spintronics”. We receive additional support from US ONR, as well as through scholarships from the Alexander von Humboldt Foundation and oth-er foundations specialized for the promotion of young scientists.

The groups at our chair maintain extensive col-laborations with theory groups in the State Uni-

versity of New York in Buffalo, the Duke University, Harvard University, University of Maryland, College Park, Université Louis Pasteur in Strasbourg, Uni-versité Paris-Sud in Orsay, Karl-Frenzens University in Graz, University of Leoben, the University Cata-nia and the Hefei Institute of Technology in China.

Further information regard-ing research, publications, and participating staff can be found at:

http://www.physik.uni-regensburg.de/forschung/fabian/

http://www.physik.uni-regensburg.de/forschung/richter/richter/

Tunneling anisotropic magnetoresistance: experiment group of D. Weiss and our theory

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Calculated spin relaxation in coupled quantum dots

Consistent calculation of the local density of state of a three barrier magnetic resonant tunnel diode at an applied bias.

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The fundamental theoretical concepts of parti-cle physics are based on Quantum Field Theo-

ries (QFT) (see for example the article ‚Quanten-feldtheorie - Was ist das?‘ at the internet portal of the Federal Ministry: http://www.weltderphysik.de,search item ́ Quantenfeldtheorie´). QFTs enable us to relate most basic facts of our world to some-times rather subtle experimental observations, ranging from the smallest length scales to cosmo-logical ones. A prominent example led to the 2006 Nobel prize award: From tiny fluctuations in the 3K-cosmic background radiation one could derive that the mass density of our universe is dominat-ed by exotic forms of energy/mass associated with a non-trivial vacuum structure of the type which is quite typical for unified QFTs. In perturbation theory, QFTs are well understood and, for all ef-fects which can be described perturbatively, future progress lies in the continuous and systematic im-provement of this technique. This progress also improves the chance of finding ńew physics´, re-lated to new and even more fundamental levels of our ´Grand Picture´ of the world. (Basically, the theoretical uncertainties have to be smaller than the magnitude of the observable effects.) There-fore, the so-called ´High-Energy Frontier´ is at the same time also a ´High-Precision Frontier´. However, although there is no doubt about the fundamental relevance of perturbative QFT, the plethora of non-perturbative phenome-na exerts the greatest fascination. In particular, in quark-gluon physics, or Quantum Chromodynam-ics (QCD), there still exist many unsolved puzzles and mysteries. QCD has a very complex phenom-enology because the relevant coupling constant as is large (typically as(Q2) = 0.2 - 0.3 instead of, e.g., a(Q2) = 1/137 - 1/120 for the electromag-netic interaction) and because the theory is funda-mentally non-linear. Within this general setting, our group works primarily on problems of non-perturbative QCD, complemented by a number of activities in perturbative QCD. By far the most universal and most well-defined non-perturbative approach to QFTs is lattice QFT, especially lattice QCD. Here, a finite space-time volume is discretized as a lattice of points. In this approximation most of the infor-mation which characterizes the inner structure of bound states, e.g., the proton, can be calculated numerically. However, for this task one needs the most powerful computers in the world. Therefore, our group is also involved in the development of new cheap and far more powerful generations of computers. At the moment, we put much hope in a project concerning a Petaflop/s computer, which we pursue in collaboration with IBM Germany, the research center Jülich, DESY, and the Univer-sity of Wuppertal. Regensburg is the seat of a non-regional DFG-Forschergruppe. Together with the University of Wuppertal, we have also applied for a Sonder-

forschungsbereich (Transregio) (spokesperson A. Schäfer). We are involved in EU projects (I3HP within FP-6) and work closely together with ex-periments at international research centers (DESY, CERN, GSI, JLab, BNL). Let us end this short sketch with just two concrete examples for our research. Unfortunately, to fully appreciate these results re-quires a certain familiarity with particle physics. (Again, we refer the interested reader to the inter-net portal of the BMBF, where a number of articles for the general public can be found.)

The first example concerns what is called GPDs (Generalised Parton Distributions).

Protons have spin 1/2 and, to a good ap-proximation, they consist of two up quarks and one down quark, which also have spin 1/2. When the three quark spins couple to an overall spin 1/2, their relative angular momenta result in a non-triv-ial spatial distribution of the quarks. This can be

computed making use of nothing but the funda-mental equations of QCD. On the left hand side, the predicted density distribution of the quarks in the transverse plane is plotted for a proton, which flies towards you and whose spin points to the right. On the right hand side, however, the spin of the observed quark points to the right, while there is no restriction concerning the direction of the proton spin. The second example concerns confine-ment, i.e., the fact that quarks and gluons can-not exist as free particles, but only as ćolorless´ bound states. If one tries, for example, to separate a quark and an antiquark, a so-called string of glu-ons forms, which breaks at larger separations and generates a new quark-antiquark pair. Also this ef-fect can be calculated in detail free of any assump-tions. Fig.2 shows a resulting ´snapshot´.

Prof. Dr. Vladimir BraunHadron- and Particle Physics


Prof. Dr. Tilo Wettig


Fig. 1: GPDsDistribution of quarks in a transversely polarized (left) and unpolari-

zed (right) proton.

Quantum Chromodynamics - The Theory of Quarks und Gluons Professors: Dr. Gunnar Bali, Dr. Vladimir Braun, Dr. Andreas Schäfer, Dr. Tilo Wettig

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Figure 3 shows the Regensburg QCDOC computer, which has been developed by IBM, BNL, RIKEN, Columbia University, and the British na-tional lattice collaboration, and by T. Wettig, who was a professor at Yale/RIKEN-BNL at the time. The computer in Regensburg is hardly larger than a workstation but provides 0.4 Teraflop/s. (Its ´big-ger brothers´ in the US and in the UK have typical-ly 10 Teraflop/s.) Meanwhile, we work on a succes-sor with a price-performance ratio which will be better by more than one order of magnitude and which should have an especially low energy con-sumption per Teraflop/s.

Prof. Dr. Andreas SchäferHadron- and Particle Physics


Prof. Dr. Gunnar Bali


Fig. 2: String-Breaking The gluon string between a quark and an antiquark just before it breaks to generate a new quark-antiquark pair.

Fig. 3: QCDOC The Regensburg QCDOC-computer

Akad. Dir. Josef Reisinger


Didactics of PhysicsAkad. Dir. Josef Reisinger

“Man kann einem Menschen nichts lernen, man kann ihm nur hel-fen, es für sich selbst herauszufinden.“ Galileo Galilei

The didactics of physics not only represents an independent subject. Above all, it provides

the scientific component of the profession of the physics teacher. As a matter of course, a physics teacher must have a well-founded knowledge in this special branch of science. For the required in-terdisciplinary education, additional knowledge in the fields of other scientific disciplines and tech-nology is indispensable. And of course, they also require the relevant knowledge of the education-al, humane, and social disciplines. Anyway, the doctrine of teaching and learning physics - which represents the core activity in the physics lesson - is the didactics of physics.

The multidisciplinary science of teaching and learning methods for physics (didactics of phys-

ics) is still quite young. It has only been represent-ed as a research discipline at German Universities since the 70‘s. In contrast to physics itself, it can-not profit from a long tradition. Thus, it is under-standable that, so far, no uniform and indepen-dent scientific paradigm has emerged. Primarily, the didactics of physics deals with the question of what to communicate in physics lessons (aims/targets and legitimation of physics in school) and, regarding all aspects of the issue, how these aims can be achieved. This in-cludes, among other things, the analysis of learn-ing processes, surveying the imagination of pupils, the development of concepts/models which re-spect pupils potentials and scientific accuracy, the setup of teaching units, the design of material for experiments and teaching media, along with their testing and scientific evaluation. Roughly speaking, two different direc-tions of the didactics of physics can be distin-guished: the physics, focusing on the scientific subject, and the didactics of physics, emphasizing the empirical research in the field of teaching and learning. In Regensburg mainly teaching tasks are part of the didac-tics of physics. Apart from the theoretical and practical education of the students in spe-cialized didactics within the scope of the courses for primary and second-ary schools, the organi-zation and realization of advanced trainings for teaching staff, as well as the collaboration with schools, form the core themes. During the prep-aration for their final examinations, the students deal with the decomposition of the subject matter, the construction of teaching units, as well as the development of learning material and media for the classes. These are tested in practice and evalu-ated with respect to their usability.

pedagogicsgeneral didactics

psychologysociology

(natural-) philosophyscience theory

theory of cognition...

physicschemistrybiologytechncs

technology...

didacticsof

physics

physicslessons

Model experiment for an uncon-trolled chain reaction (matches, stick to a metal plate)

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The courses offered for the students include

• introduction to school physics, taking into ac-count specialized didactical aspects for an educa-tion concerning certain branches of science• the lecture „Introduction to didactics of phys-ics“ (procurement of theoretical basics of special-ized didactics)• a lecture focusing on the introduction of ba-sic physical terms (for example, the terms of force, energy, ...); this is particularly about the subject- and pupil-suitable simplification/visualization of central physical concepts• experimental seminars for the planning, set-up, performance, and presentation of physical ex-periments in school, as well as their reflection with respect to a specialized didactical point of view• seminars for the analysis and planning of lec-tures, particularly in combination with classroom experience• a seminar to prepare for the written final ex-aminations

In many activities video recordings are used as a basis for the reflection.

The organizational structures of the didactics of physics are geared to the ideal of learning work-shops. Rooms for seminars, labs and experimen-tal equipment, a reference library, working mate-rial, media, a room for communication, and open doors shall setup an environment for learning which encourages independent learning. The reflection on classes using video re-cordings gains more and more importance for specialized didactical research and development. Currently, a continuing education for teachers is carried out in collaboration with the Institute for

Science Education (IPN) in Kiel, where teachers are instructed to reflect upon their own lessons with the assistance of video recordings. The intention of the intervention is to assist the teachers in mak-ing themselves aware of their patterns of thoughts about physics lessons and in sustainably control-ling them. The main challenge for the instruction in school physics is not to turn pupils into little physi-cists or even more to advance physics. In fact, pu-

pils should get an idea of what physicists do and how physics evolves. They can only do so when the physics lessons are aimed for comprehensible learning. Therefore, some basics of physics have to be learnt. However, already Max Planck realized: „It‘s not a matter of fact what is learnt in school, but how it is learnt. A single mathematical theo-rem, which really is understood by a pupil, is of more value for him than ten formula which he has learnt by heart and which he can apply according to the rules, without understanding their intrinsic meaning.“ For the physics lessons as well, the most exclusive and important task is to accompany young people during their personal development. Therefore, the specialized didactical training deals not only with the optimization of all proper phys-ics lessons, but also with the discussion of ques-tions about norms and values. Apart from the con-tents, the physics teacher always has to keep an eye on pupils who wish to engage in constructive discussion about the material. Therefore, to incite a new spirit in connection with the term “physics lessons” actually means to gear lessons towards pupils at large.

Hands-free experiment for the expansion of gases at heating. At the same time, the trial demonstrates the transformation of thermal into mechanical energy.

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Norbert SommerWorkshop supervisor


Johann DeinhartAssistant workshop super-visor


Mechanical Workshop

Norbert Sommer, Johann Deinhart

The mechanical workshop is of utmost impor-tance for the experimental physicist. During the

PhD work in particular, but also during the masters thesis, often completely new apparatus have to be set up in order to be able to perform the planned experiments (Fig. 1 and 2). Therefore, frequently non-customary gadgets and components are nec-essary which have to be developed and construct-ed in collaboration with the mechanical workshop. Furthermore, there is hardware which sooner or later “gives up the ghost” and necessitates repair. The mechanical workshop provides stores for raw material, screws, elements for machines and so on, which are shared with all students.

We are the technical service providers for the experimental research in the physics de-

partment. Most technical problems can be solved quickly and without bureaucracy due to the close vicinity of the mechanical workshop to the labora-tories. The direct contact between scientists and mechanics works to the advantage of both. For larger projects, it is necessary to charge the chair technician with the planning. With the aid of modern CAD systems, the com-pleted model can be inspected on the computer and possible motion sequences can be simulated. Errors can easily be detected and corrected before-hand. For 2D drawing we are in favor of AutoCAD, for 3D models we use Inventor, both products of the Autodesk company. The instrumentations and size of the me-chanical workshop are geared to the requirements of the research. At the moment, two foremen, two craftsmen and six apprentices are contracted.

The workshop is subdivided in the following work spaces:

General workshop area:• Manufacturing of elementary components from various substances with conventional machine-tools (Fig. 3). • Assembly and repair of machines and gadgets• Apprenticeship training positions for industry mechanics (Fig. 4)

Locksmith - Welding shop• Manufacturing of fixtures (racks, chassis, tables, shields) of steel, aluminum, wood and synthetic material• Welding of vacuum chambers, muffs, tubes and accessories

CNC Center• Computer-controlled lathe and milling machine for the fabrication of complex mechanical components, as well as for mass-production (Fig. 5). • Computer-controlled wire erosion machine for contour cutting and for dividing of all types of metal substances with a cutting clearance of 0.2 to 0.4 nm Superfinishing of components with high dimension accuracy and surface finish/roughness

Surface engineering• drum grinding: deburring, grinding and polishing of metal bits and pieces• anodizing: purifying of surfaces of aluminum (possible with various colorings)• browning: nigrification of the surface of brazen pieces• varnishing of sheet metal components up to a size of about 1m^2 (Fig. 6)

Fig. 2

Fig. 1

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Organization of trainings for pupils and students• for pupils: work experience week • for students: instruction in the basics of metal machining (lathing, milling, sawing, drilling, tapping, among others)

Fig. 5

Fig. 4

Fig. 3

Fig. 6

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Naturwissenschaftliche Fakultät IIPhysikUniversität Regensburg

93040 Regensbug

Telefon: ++49 (0) 941 943 2023Telefax: ++49 (0) 941 943 2021

Internet: http://www.physik.uni-regensburg.de

Impressum

HerausgeberNaturwissenschaftliche Fakultät II - PhysikUniversität Regensburg

VerantwortlichProf. Dr. Klaus Richter, Dekan

Redaktion / TextBeiträge der Arbeitsgruppen

ÜbersetzungTommy Burch, Christoph Bauer

GestaltungFranz Stadler, Universität Regensburg

FotosBeiträge der Arbeitsgruppen, Christoph Bauer

© 2007, Naturwissenschaftliche Fakultät II - PhysikUniversität Regensburg

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de en · Collaborative Research Centers „Spin phenomena in reduced dimensions“ of the German Research Foundation, further corporate research activities ... this conference has