Experimental Physics V
Chair News
Universalities at the glass transition
In a recently published article in the leading physics journal "Nature Physics", PD Dr. Peter Lunkenheimer and Prof. Dr. Alois Loidl, together with colleagues from Göttingen, Berlin and Milan, report about unexpectedly universal correlations between the thermal expansion and the glass-transition temperature of glass-forming materials, providing new insights into the complex nature of the glass transition.
Although glasses belong to the oldest materials used by mankind, the microscopic processes at the transition of a glass into a liquid (or vice versa) are not well understood. By analysing the thermal expansion and the glass-transition temperatures of more than 200 glasses and liquids, the physicists now found evidence that the solid-liquid transition of glasses is strongly influenced by the fact that the motion of the atoms or molecules in a glass-forming liquid typically is "cooperative" (i.e., the particles do not move independently). This can lead to a significant increase of the energy needed to liquefy a glass. Moreover, the researchers find another, surprisingly universal correlation: The thermal expansion in the liquid state is by a universal factor of about 3 larger than in the glassy state of a material, although the expansion in both states of matter is commonly believed to be governed by fundamentally different mechanisms.
Overall, the found universalities will significantly contribute to a better understanding of such different materials as silicate-based everyday glasses, polymers, and metallic glasses.
More info (press release of the University of Augsburg)
Geladene ferroelektrische Domänenwände als Schaltelement für die Nanoelektronik
Domänenwände für die Nanoelektronik
Ferroelektrische Domänenwände sind im Forschungsfokus der Nanoelektronik für „schlanke“ Bauteile. Die elektronisch funktionalen Wände erlauben es miniaturisierte Komponenten für Schaltkreise, wie Schalter, Dioden oder Kondensatoren, in einem „einzigen“ Material zu designen.
Die neuesten Forschungsergebnisse der Forschungskooperation zwischen Physikern und Materialwissenschaftlern der Universität Augsburg und der Norwegian University of Science and Technology (NTNU) in Trondheim zeigen nun auch, dass, so Prof. Dr. Dennis Meier „neben klassischen DC (direct current) Komponenten auch AC (alternating current) Bauteile, wie Thyrectoren oder Dioden mit funktionalen Wänden realisiert werden können.“ Dies stellt so nach PD Dr. Stephan Krohns „einen wichtigen Schritt dar, um eine Verbindung zwischen aktiven und passiven Komponenten mit diesen ferroelektrischen Domänenwände zu erstellen.
Neue Messmethode
Zu diesen Erkenntnissen gelangte das internationale Team durch Untersuchungen an dem hexagonalen Manganat ErMnO3 mithilfe der erst kürzlich entwickelten Mikroskopie Methode AC-cAFM. „Es handelt sich hierbei um eine Weiterentwicklung der Standard-Mikroskopie-Technik Conductive Atomic Force Microscopy, bei der eine AC Spannung an die Probe angelegt wird, während das zur DC Komponente gehörende Stromsignal gemessen wird.“ berichtet Dr. Jan Schultheiß. „Durch Kombination spannungsabhängiger spektroskopischer Messungen auf makroskopischer und lokaler Skala zeigen wir ein ausgeprägtes nicht-lineares Verhalten am Elektroden-Wand-Übergang, das mit dem Domänenwand-Ladungszustand korreliert.“ berichtet Lukas Puntigam.
Vielseitige Anwendungsbereiche
Die Arbeit „Charged Ferroelectric Domain Walls for Deterministic ac Signal Control at the Nanoscale“ erschien kürzlich im Journal Nano Letters. Basierend auf diesen Ergebnissen scheinen vielseitige Anwendungsbereiche für Domänenwände für elektronische AC Bauelemente im Kilo- bis Megahertz Bereich möglichen zu werden. Dies stellt einen weiteren wichtigen Schritt in der Charakterisierung der elektronischen Eigenschaften und ihrer Transportphänomene in ErMnO3 im Hinblick auf das Anwendungsgebiet der Nanoelektronik dar.
Malaria: Physiker entwickeln neue Diagnose-Methode
„Augsburg/FL/MH – Physiker der Universität Augsburg haben mit Kollegen von der australischen James Cook University eine neue Diagnose-Methode auf Malaria entwickelt. In einer Feldstudie in Papua-Neuguinea haben sie das Verfahren nun an rund 1000 Personen getestet. Demnach ist es ähnlich treffsicher wie etablierte Ansätze und zugleich sowohl kostengünstig als auch einfach in der Handhabung. Die Studie ist nun im renommierten Fachjournal Nature Communications erschienen.“
KI bringt Materialforschung für Nanoelektronik voran
„Die zukünftige Elektronik benötigt miniaturisierte und multifunktionale elektronische Bauteile, die ohne komplexe Materialkombinationen realisiert werden können. Domänenwände stehen hierbei im Fokus der Materialforschung, da diese Wände Grenzflächen auf Nanometerskala zwischen Bereichen gleichmäßiger Orientierungen, z.B. ferroelektrische Polarisation, darstellen.“
Mehr Infos
Projekt „Pawsthesis“
„Augsburg/BB – Wenn dem „besten Freund des Menschen“ eine Pfote oder gar ein ganzes Bein fehlt, ist das eine Qual für Tier – und auch für die Halter. Zwei Studierende der Universität Augsburg entwickeln im Rahmen des Projekts „Pawsthesis“ Prototypen von Beinprothesen. Dies könnte mittelfristig eine gute Lösung für derart gehandicapte Hunde werden.“
Mehr Infos
Dielectric ordering of water molecules arranged in a dipolar lattice
In a recently published paper in "Nature Communications", together with scientists from Moscow, Novosibirsk, Prague, and Stuttgart, we solve the long-standing question whether the dipolar water molecules can spontaneously order parallel, thus forming a ferroelectric state. Such an exotic state of water is thought to be of high relevance in various natural systems and also might enable future applications in biocompatible nanoelectronics. In a joint experimental effort, we could show that separate H2O molecules, enclosed within nanosized channels in a crystal of the beryl family, indeed can form such a state.
More info
Macroscopic manifestation of domain-wall magnetism and magnetoelectric effect in a Néel-type skyrmion host
Geometrical or dimensional constraints can promote the formation of new quantum phases which are absent in bulk systems. Such constraints can be imposed naturally via mesoscale domain patterns or topological defects on the atomic scale. By combination of detailed magnetoelectric and magnetic torque measurement and supported by neutron scattering and real space imaging experiments we found an additional magnetic state in Skyrmion host material GaV4Se8 which emerges at polar domain walls. A clear anomaly in the magneto-current indicates that the DW confined magnetic states also have strong contributions to the magnetoelectric response. We expect polar domain walls to commonly host such confined magnetic edge states and, thus, offer a fertile ground to explore novel forms of magnetism.
Magnetoelectric spectroscopy of spin excitations in LiCoPO4
Magnetoelectric spectroscopy is a powerful tool to determine all off-diagonal elements of the magnetoelectric tensor in a contactless fashion. Our colleagues demonstrate the efficiency of this optical method by measuring the off-diagonal magnetoelectric response of LiCoPO4 in the GHz-THz regime. According to their finding, the magnetoelectric effect in this antiferromagnet is dominated by the symmetric (quadrupolar) part of the magnetoelectric tensor.
Ferroelectricity in vectorchiral phases
Chirality, that is the handedness of objects is acknowledged for its great importance in many fields of biology and chemistry. However, chirality also plays a huge role in physical phenomena, e. g. symmetry aspects of frustrated magnets. In case of noncollinear magnetic ground states, spin-spirals may emerge. It is predicted for these states, that even above the magnetic ordering temperature, so-called vectorchiral phases emerge, which feature an ordered spin rotation (either of clockwise or anticlockwise fashion) between neighbouring spins, still there is no explicit relation concerning the angle spanned by neighbouring spins. By means of magnetic field dependent polarization measurements, we are the first to provide proof for the emergence of this phenomenon in LiCuVO4, a one dimensional quantum magnet with concurrent ferromagnetic and antiferromagnetic exchange interactions (marked as "VC" in the attached phase diagram). This proof relies on the fact that the vectorchiral state implies a finite ferroelectric polarization at temperatures above the ordering of the three dimensional spin-spirals.
Optical pumping of magnetic skyrmions
GaV4S8 is a multiferroic semiconductor hosting magnetic cycloid (Cyc) and Néel-type skyrmion lattice (SkL) phases with a broad region of thermal and magnetic stability. Here, we use time-resolved magneto-optical Kerr spectroscopy to show the coherent generation of collective spin excitations in the Cyc and SkL phases. Our micromagnetic simulations reveal that these are driven by an optically induced modulation of uniaxial anisotropy. Our results shed light on spin dynamics in anisotropic materials hosting skyrmions and pave a new pathway for the optical manipulation of their magnetic order.
Research Topics
Our group covers a broad field of investigations in condensed matter physics. We focus on new materials for future electronics, on unconventional ground states, superconductors, the dynamics of disordered matter and biological materials.
Experimental Methods
Aside of a large number of sample characterization methods, a strong point of our group is the combination of a variety of spectroscopic methods enabling deep insight into the microscopic properties of condensed matter. This not only includes dielectric, THz, and optical spectroscopy but also electron and nuclear magnetic resonance techniques.
National and International Collaborative Research Projects
Our group participates in several specially funded collaborative research projects:
Sino-German Cooperation on Emergent Correlated Materials
The Sino-German Center for Research Promotion (SGC) is funding a cooperation project on electronically highly correlated materials, which is conducted by Zhejiang University (Hangzhou) and the University of Augsburg.
Ressourcenstrategische Konzepte für zukunftsfähige Energiesysteme
The graduate school "Ressourcenstrategische Konzepte für zukunftsfähige Energiesysteme" provides funding for PhD students, who carry out research on essential topics regarding future energy and supply systems.
Contact
General Contact Information:
Address (Secretary Office):
Christine Mayr
(Room 308, 3rd floor)
Universitätsstrasse 1
D-86159 Augsburg
Germany
Telefon: +49 821 598 -3602
Fax: +49 821 598 -3649
E-Mail: christine.mayr@uni-a.de
Mailing Address:
Experimentalphysik V
Institut für Physik
Universität Augsburg
Universitätsstrasse 2
D-86135 Augsburg
Germany
Delivery Address:
Experimentalphysik V
Institut für Physik
Universität Augsburg
Universitätsstrasse 1
D-86159 Augsburg
Germany
Map and Directions:
The Department of Experimental Physics V is located in the building S of the Institute of Physics at the University of Augsburg. The secretary's office is in room 308 on the 3rd floor.
How to reach us with public transportation:
From Munich Airport take the city train S8 or the
Airport Bus to reach "München Hauptbahnhof". Then take the
train to "Augsburg Hauptbahnhof".
From "Augsburg Hauptbahnhof" take
tram route 3 in the direction of "Haunstetten West". The tram stop "BBW/Institut für Physik" is located directly in front of the building.
How to reach us by car:
Leave the B17 at exit "Messe/Universität" and turn right into Universitätsstraße directly afterwards. After about 1 kilometer turn right into Hertha-Sponer-Weg between the buildings T and R.
Parking spaces are located along the buildings R and S as well as at the end of the street (P9).
