Institut für Theoretische Physik und Astrophysik (ITAP)

Welcome to the web page of the Institute of Theoretical Physics and Astrophysics (ITAP) of Kiel University. Theoretical physics in Kiel has a long tradition. Among former members are Max Planck (founder of quantum theory and Nobel laureat), Heinrich Hertz and Albrecht Unsöld.

Today ITAP has two divisions: Astrophysics and Theoretical Physics. Undergraduate and graduate education covers the full spectrum of this fields. Research at ITAP is focused on extragalactic astrophysics, planet and star formation, plasma physics, many-body theory, nanoscience, spintronics, density functional theory and surface physics. We use state of the art methods including large-scale simulations on supercomputers and observations on large telescopes worldwide.

For more details on teaching and research, please, visit the web pages of the division of Astrophysics and Theoretical Physics or of the research groups.

Discovery of a spontaneous atomic-scale magnetic skyrmion lattice in two dimensions

Skyrmions are topologically protected field configurations with particle-like properties which play an import ant role in various fields of science ranging from elementary particles to condensed matter physics. Particularly excit ing was the recent discovery of skyrmions in magnetism observed in a special class of magnetic bulk alloys: MnSi, FeGe, and CoFeSi. In these systems a lattice of skyrmions on the scale of 20 to 90 nm was induced by an external magnetic fiel d. In contrast, the group of Stefan Heinze in collaboratio n with colleagues from the University of Hamburg and the Forschungszentrum Jülich now reports in Nature Physics the observation of an atomic-scale magne tic skyrmion lattice as the spontaneous ground state of an ultra-thin film on a surface. This discovery opens new vistas to locally probe and manipulate the static, dynamic, and spin transport properties of topologically protected spin text ures at surfaces or interfaces.
Image: Courtesy of M. Menzel (Univ. Hamburg).

Superfluidity of nonideal bosons with dipole interaction

A many-particle system of Bose particles is known to form a superfluid state below a critical temperature which is characterized by a loss of the viscosity of the system (similar to superconductivity in fermionic systems). This has been well studied for weakly interacting systems. In case of strong interaction, which is currently becoming of increasing interest for ultracold atoms and molecules, the properties of this phase transition are still poorly understood. Now a work led by Priv.-Doz. Alexei Filinov (ITAP), performed together with Prof. Michael Bonitz (ITAP) and Nikolay Prokof'ev (Massachusetts), answers many of the open questions. In a paper published in Physical Review Letters they reported first principle quantum Monte Carlo results for the phase diagram and single-particle energy spectrum of nonideal dipolar bosons in two dimensions and predict the experimental parameters where to observe the normal to superfluid transition.

Nichtlineare Magnetoplasmonen in stark korrelierten Yukawa Plasmen

Das Eigenmoden-Spektrum ist eine wichtige Eigenschaft eines Vielteilchensystems, insbesondere bei Vorliegen starker Korrelationen. Für magnetisierte Yukawa-Systeme wurde es bereits vor einigen Jahren theoretisch und mit Simulationen bestimmt. Genauere first principle Molekulardynamik-Simulationen haben aber jetzt gezeigt, dass im Spektrum zusätzliche Moden existieren - höhere Harmonische des Magnetoplasmons. Die neue Veröffentlichung in Physical Review Letters beschreibt diese Moden, die an die bereits 1958 vorhergesagten klassichen Bernsteinmoden erinnern. Im Gegensatz zu letzteren, die für ein schwach korreliertes Plasma gültig sind und bei Vielfachen der Zyklotronfrequenz auftreten, zeigen die neuen Dispersionsüste aber unmittelbar den Einfluss von Korrelationen - ihre Frequenz ist eine Kombination aus Zyklotron- und Einsteinfrequenz. Die Resultate sind relevant für Laborplasmen (staubige Plasmen) und astrophysikalische Plasmen in kompakten Sternen. Die Abbildung zeigt das Frequenzspektrum (Strukturfaktor) mit 3 Harmonischen des Magnetoplasmons.

Millionenzusage für Forschung mit Synchrotronstrahlung

Arbeitsgruppen der Kieler Physik erhalten in den nächsten drei Jahren ca. 3 Mio. Euro Fördergelder für Projekte zur Forschung mit den neuen Röntgenstrahlungsquellen am DESY in Hamburg. Die geförderten Vorhaben starten am 1. Juli und werden innovative Instrumentierungen für den Freie-Elektronen-Laser in Hamburg (FLASH) und die neue Synchrotronstrahlungsquelle PETRA III entwickeln und aufbauen sowie rechnergestützte Simulationen durchführen. Vom ITAP ist die Arbeitgsruppe von Prof. Bonitz beteiligt:
Theoretische Untersuchung und Simulation der Photoionisation kleiner Atome und Moleküle durch UV-Strahlung und Erarbeitung theoretischer Vorhersagen als Grundlage für aktuelle und künftige Experimente bei FLASH, PETRA III und XFEL (Prof. Bonitz).

Links:

Artikel der AG Bonitz am 5.01.2010 in Physical Review Letters erschienen.

"How Spherical Plasma Crystals Form"

Three-dimensional plasma crystals consisting of charged particles arranged on concentric spherical shells have been observed in a variety of systems, including laser-cooled neutral plasmas, ions in traps or dusty plasmas. Whereas in the former case it was observed that shell formation starts in the center of the plasma cloud, in the latter two systems shells always emerge at the outer plasma boundary. The present paper explains the origin of these differences. It presents a full time-dependent analysis of the crystallization process for the example of a confined dusty plasma and studies the influence of the particle interaction (Coulomb or Yukawa) and of the trapping potential. The authors demonstrate that 1) in a harmonic confinement shell formation always begins at the boundary and 2) screening of the Coulomb interaction leads to a more rapid formation of inner shells. The shell formation dynamics is shown in the figure where the interaction changes from Coulomb (e.g. trapped ions, top figure) to weak and strong screening (e.g. dusty plasmas, middle and lower part of the figure). Finally the crystallization direction was found to be governed by the shape of the confinement potential. It is shown how this knowledge can be used to control the crystallization direction in a dusty plasma.