Fakultät für Physik - News https://cms.univie.ac.at/ Feed für News der Fakultät für Physik, Universität Wien de Fakultät für Physik - News https://cms.univie.ac.at/typo3conf/ext/univie_ttnewsrss/rss_icon.gif https://cms.univie.ac.at/ 28 28 Feed für News der Fakultät für Physik, Universität Wien TYPO3 - get.content.right http://blogs.law.harvard.edu/tech/rss Mon, 06 Nov 2017 11:15:00 +0100 Lise Meitner Lecture - Nicola Spaldin: New Materials for a New Age https://cms.univie.ac.at//news/news-detailansicht/article/lise-meitner-lecture-nicola-spaldin-new-materials-for-a-new-age/?tx_ttnews%5BbackPid%5D=110280&cHash=cbb4808a68780040915b1b0a3eee8e5e Every advance in human civilization, from the Stone Age to today’s Silicon Age, has been driven by... Short Biography 

Nicola Spaldin is the Professor of Materials Theory at ETH Zurich. A native of the UK, she studied Natural Sciences at Churchill College, Cambridge and obtained her PhD in Chemistry from the University of California at Berkeley. After postdoctoral research in Applied Physics at Yale University she joined the Materials Department at University of California, Santa Barbara as Assistant, Associate then Full Professor before returning to Europe in 2010.

Spaldin developed the class of materials known as multiferroics, which combine simultaneous ferromagnetism and ferroelectricity, for which she has received the American Physical Society's McGroddy Prize for New Materials, the Körber European Science Prize and the L'Oréal-UNESCO For Women in Science Award, among others.

Spaldin is a passionate science educator, author of a popular text book on Magnetic Materials, director of her department’s study program, and holder of the ETH Golden Owl Award for excellence in teaching. When not trying to make a room-temperature superconductor, she can be found playing her clarinet, or skiing or climbing in the Alps.

Mon, 06 Nov 2017 11:15:00 +0100
Mag. Theodor Duenbostl (1946 - 2017) https://cms.univie.ac.at//news/news-detailansicht/article/mag-theodor-duenbostl-1946-2017/?tx_ttnews%5BbackPid%5D=110280&cHash=702bb43cb6b2013f827599f3755515ed Die Fakultät trauert um Herrn Mag. Theodor Duenbostl, der am 13. Oktober 2017 im 71ten Lebensjahr... Am 13. Oktober 2017 verstarb Mag. Theodor Duenbostl, Professor i.R. am BG und BRG Wien 10, langjähriger Betreuer der Studierenden im Praktikum für Schulversuche an der Fakultät für Physik der Universität Wien und langjähriger Leiter der Arbeitsgemeinschaft für Physiklehrerinnen und –lehrer an den Wiener AHS.
Er war Dozent am Pädagogischen Institut der Stadt Wien, Autor zahlreicher Lehrbücher und CD-ROM für den naturwissenschaftlichen Unterricht, Referent an den Pädagogischen Hochschulen Österreichs und Konsulent von Lehrmittelfirmen.
2006 erhielt Theodor Duenbostl den Roman Ulrich Sexl-Preis der ÖPG für besonders erfolgreiche und motivierende Lehre. Er ist auch Träger des Goldenen Ehrenzeichens für Verdienste um die Republik Österreich.

Theodor Duenbostl begann 1964 sein Studium an der Universität Wien für das Lehramt aus Physik und Mathematik nach Absolvierung der Matura an einem Humanistischen Gymnasium in Wien. Nach Abschluss des Studiums startete er seine Lehrtätigkeit am BG und BRG Wien 10 in der Ettenreichgasse, wo er bis zu seiner Pensionierung verblieb.

1974 wurde er vom Stadtschulrat Wien dem damaligen Institut für Experimentalphysik der Universität teilzugeteilt, wo er, neben seinen zahlreichen anderen Aktivitäten, als Betreuer der Studierenden im Praktikum für Schulversuche bis zu seiner Überleitung in den Ruhestand im Herbst 2009 tätig war.
Er selbst bezeichnete diesen neuen Abschnitt seines Lebens lieber als (Un-)Ruhestand, da er weiterhin als Lektor an der Universität Wien im Praktikum für Schulversuche und als Vortragender im In- und Ausland aktiv blieb.
In diesem Jahr arbeitete er z.B. noch intensiv an der Verfassung eines neuen Physik-Lehrbuches für die Unterstufe mit.

Theodor Duenbostl wird vielen Kollegen als angenehmer, lustiger Mensch und den Studierenden als inspirierender Lehrer in Erinnerung bleiben.

Mon, 06 Nov 2017 11:00:00 +0100
Greenberger-Horne-Zeilinger’s have only one twin! https://cms.univie.ac.at//news/news-detailansicht/article/greenberger-horne-zeilingers-have-only-one-twin/?tx_ttnews%5BbackPid%5D=110280&cHash=9b100a5fdf5fbf6b2c7131a1ca7da402 Beatrix Hiesmayr (Theory, Faculty of Physics) initiated an experiment now put to reality at the... For four qubits (=two-level systems) one can find a basis of 16 GHZ states (GHZ...Greenberger-Horne-Zeilinger). Surprisingly, choosing one GHZ state one always finds a twin state such that an equal mixing results in a separable state, the genuinely multipartite entanglement property is fully lost. If, however, one mixes with another GHZ state in the basis set, the resulting state does not lose all entanglement properties. This has been observed with two physical photons entangled in their polarisation and angular momentum degree of freedom (published in [1])

This system of two physical photons can be considered as a four particles system with two degrees of freedoms (=4 qubits).  Mixing GHZ states unmasks different entanglement features based on their particular local geometrical connectedness. In detail, the geometry of GHZ basis states is described by ``Schön ist so ein Ringelspiel’’) (Merry Go Round) [famous Viennese song by Hermann Leopoldi about the pleasure of using the Carousel in the Viennese Prater]. Exploiting these local geometrical relations provides a toolbox for generating specific types of multipartite entanglement, each providing different benefits in outperforming classical devices. Controlling the different types of entanglement properties of the finally generated state will be the key for novel applications.

[1] G. Carvacho, F. Graffitti, V. D’Ambrosio, B. C. Hiesmayr & F. Sciarrino, Scientific Reports 7, Article number: 13265 (2017); https://www.nature.com/articles/s41598-017-13124-6

Fri, 27 Oct 2017 11:56:00 +0200
The Faculty of Physics congratulates Philip Walther on his promotion to full professor https://cms.univie.ac.at//news/news-detailansicht/article/the-faculty-of-physics-congratulates-philip-walther-on-their-promotion-to-full-professors/?tx_ttnews%5BbackPid%5D=110280&cHash=bf431bd5a3c6aeaaf87f7aab3f795087 Philip Walther from the research group “Quantum Optics, Quantum Nanophysics and Quantum... Univ.-Prof. Dr. Philip Walther

Quantum information sciences and quantum computation:

The research of the group of Philip Walther focuses on the development of advanced photonic quantum technology for applications in quantum information processing and for investigations in quantum science. The fact that photons have an intrinsic lack of decoherence and that they can be conveniently manipulated with high precision, makes them attractive for many applications. The photons’ inherent advantage of being mobile provides a unique opportunity of transmitting and processing quantum information by using the same physical system.

Our current activities are centered on secure quantum cloud computing and quantum-secure classical computers on one hand, quantum computation and quantum simulation on the other hand. Apart from that the research projects also focus on quantum foundations and indefinite causal structures as well as nonlinear photonic quantum gates and cluster state generation using solid-state single-photon sources as well as measurement of weak gravitational effects on single photons.

About Philip Walther:

Philip Walther was born 1978 in Vienna, Austria.


2012      Habilitation in Quantum Optics, Faculty of Physics, University of Vienna, Austria

2005      PhD (Dr. rer. nat.) in Physics; University of Vienna, Austria (with A. Zeilinger)

2002      Diploma (Dipl-Ing.) in Chemistry, Vienna University of Technology, Austria (with K. Schwarz)

Current Positions

01/2017 –            Speaker of Research Platform TURIS, Faculty of Physics, University of Vienna

10/2015 –            Professor of Physics, Faculty of Physics, University of Vienna

10/2014 –            Vice-Dean of the Faculty of Physics, University of Vienna

07/2013 –            Speaker of the Quantum Optics, Quantum Nanophysics, Quantum Information Group, Faculty of Physics, University of Vienna

Career History

2013 – 2015        Associate Professor (tenured), Faculty of Physics, University of Vienna

2011 – 2012        Assistant Professor (tenure-track), Faculty of Physics, University of Vienna

2008 – 2011        Assistant Professor (Univ.-Ass.) Faculty of Physics, University of Vienna

2005 – 2008        Postdoctoral Researcher, Department of Physics, Harvard University, USA (with M. Lukin)

Honors and Awards

2014                      Recognition Award for Science 2014 by Lower State Austria

2014                      Visiting Professor Fellowship by the Brazilian Federal Government

2011                      Vienna Funding Award in Science (Förderungspreis der Stadt Wien)

2011                      START Prize, Austrian Ministry of Science and Education (BMWF)

2009                      Fresnel Prize, European Physical Society (EPS)

2006                      Prize for outstanding academic performance, University of Vienna

2005                      Loschmidt Prize, Chemical-Physical Society of Vienna


2015                      American Physical Society, Fellow

2014                      Austrian Academy of Sciences - "Junge Akademie" (Young Academy), Member

2012                      The Global Young Academy, Member

2007 – 2012        The German Young Academy at the Berlin-Brandenburg Academy of Sciences and the German Academy of Natural Scientists Leopoldina, Alumni Member

Further information:




Fri, 27 Oct 2017 11:38:00 +0200
The Faculty of Physics congratulates Cesare Franchini on his promotion to full professor https://cms.univie.ac.at//news/news-detailansicht/article/the-faculty-of-physics-congratulates-cesare-franchini-on-their-promotion-to-full-professors/?tx_ttnews%5BbackPid%5D=110280&cHash=35e85a4a5bc603e8821d45f3ee1de1bf Cesare Franchini from the research group “Computational Materials Physics” has been appointed full... Univ.-Prof. Dr. Cesare Franchini

Quantum modelling of materials using first principles computational methods:

The research work of the group of Cesare Franchini is concerned with the theoretical understanding and computational modelling of quantum materials (bulk and surfaces) using first principles methods. Quantum materials are systems with many interacting degrees of freedom (lattice, spin and electron orbital) that represent a rich platform for the discovery of novel electronic and magnetic phases with fundamental and applicative interest. Specific topics include: Metal-insulator transitions, Polaron physics (electron-phonon interactions), non-collinear spin orderings, topological Dirac/Weyl phases, multiferroism and superconductivity; number of publications: ~100, h-index: 28.

About Cesare Franchini:

Born 1975 in Modena, Italy


1999            MSc in Physics, University of Cagliari (Italy)
2002            PhD in Physics, Technical University of Vienna (Austria)

Current Position

2017-           Full Professor “Quantum Materials Modelling”, University of Vienna

Career History

2002-2004   Postdoc, University of Cagliari, Italy
2004-2007   Postdoc, University of Vienna, Austria
2007-2012   University Assistant, University of Vienna, Austria
2012-2014   Assistant Professor (Tenure Track), University of Vienna
2013            Parental Leave
2013            National Scientific Habilitation in Theoretical physics of matter, Italy
2014-2017   Associate Professor, University of Vienna

Honors and Awards

2010            Young International Scientist Fellowship, Chinese Academy of Sciences

2015            Outstanding Referee for the journals of the American Physical Society

2017            Shield of honor, Abbottabad University, Pakistan

Further information:



Fri, 27 Oct 2017 11:34:00 +0200
Nanopartikel: Physiker bestätigten fast 80 Jahre alte Vorhersage https://cms.univie.ac.at//news/news-detailansicht/article/nanopartikel-physiker-bestaetigten-fast-80-jahre-alte-vorhersage/?tx_ttnews%5BbackPid%5D=110280&cHash=ea8e02f901940a3c17f8d38fc61d933b Forscher der Universität Wien (Christoph Dellago, Computational Physics) sowie aus der Schweiz und... Betrachtet man kleinste Partikel in Flüssigkeiten oder Gasen unter einem Mikroskop, dann sieht es aus, als ob sie sich wie von Geisterhand bewegen. Nach ihrem Entdecker, dem schottischen Botaniker Robert Brown, wurde der Effekt als "Brownsche Bewegung" bekannt. Ausgelöst wird sie von der ungeordneten Wärmebewegung der umgebenden Moleküle, welche das Brownsche Teilchen sozusagen ständig anrempeln.

Zwei gegensätzliche Effekte steuern Bewegung

Wie stark die Bewegung ausfällt, wird von zwei widerstreitenden Effekten bestimmt: Einerseits erzeugen die Zusammenstöße mit den umgebenden Molekülen Reibung, die die Nanopartikel verlangsamt, andererseits treibt die bei steigender Umgebungstemperatur zunehmende Unruhe die Bewegung an.

Dieses Gegenspiel von Reibung und Wärmebewegung beeinflusst auch Übergänge zwischen unterschiedlichen Zuständen eines Systems, etwa bei chemischen Reaktionen. Damit ein solcher Wechsel stattfinden kann, muss oft eine gewisse Energiebarriere überwunden werden, welche schnelle Wechsel zwischen den Zuständen verhindert. Ist ein Teilchen sozusagen über den Berg, vollzieht sich die Veränderung sprunghaft. Wie die Übergänge aber genau von Statten gehen bzw. unter welchen Umständen Partikel wie wechselfreudig sind, ist für Phasenübergänge, den Ablauf von chemischen Reaktionen oder die Faltung von Proteinen von Bedeutung.

Höchste Übergangsrate bei mittlerer Reibung

Der niederländische Physiker Kramers zeigte einerseits, dass die Übergangsrate sinkt, je höher die Barriere zwischen beiden Zuständen ist, was so weit logisch ist. Betrachtet man jedoch den Einfluss der Reibung auf die Übergangsrate, ist der Zusammenhang weniger einfach: Gibt es geringe Reibung, sind demnach die Übergänge selten, weil das System nur langsam Energie aus der Umgebung ziehen kann, um die Barriere zu überspringen. Interessanterweise sind solche Sprünge bei großer Reibung ebenso selten, weil dann die Bewegung des Systems selbst sehr langsam ist. Am höchsten ist die Übergangsrate bei mittlerer Reibung, weil dann wieder Schwung hineinkommt und ein Partikel genug Energie sammeln kann, um die Barriere zu überwinden. Den Punkt mit der höchsten Sprung-Wahrscheinlichkeit bezeichnet man als "Kramers Turnover" (Kramers Wendepunkt).

"Kramers Turnover" exakt vorhergesagt

Die Wissenschaftergruppe um Lukas Novotny (ETH Zürich), der auch der Physiker Christoph Dellago von der Universität Wien angehörte, hat sich mit einem Experiment an die Fersen dieses ominösen Punktes geheftet. Dazu hielten sie ein frei schwebendes Nanopartikel in einer Laserfalle fest. Diese war so aufgebaut, dass sozusagen zwei Töpfe entstanden, die von einer Energiebarriere getrennt waren. Das Teilchen in der Falle stieß immer wieder mit den Gasmolekülen in seiner Umgebung zusammen. Die Wissenschafter regulierten die Reibung, indem sie den Druck des Gases exakt variierten, und zeichneten auf, unter welchen Bedingungen das Nanoteilchen wie häufig den Topf wechselte. Tatsächlich fanden die Wissenschafter "Kramers Turnover" genau dort, wo der Physiker ihn in seinen theoretischen Berechnungen vor 77 Jahren vorhergesagt hat. (APA/red)

Die Publikation "Direct measurement of Kramers turnover with a levitated nanoparticle" (Autoren:
Loïc Rondin, Jan Gieseler, Francesco Ricci, Romain Quidant, Christoph Dellago and Lukas Novotny) erschien im Oktober 2017 in der Fachzeitschrift "Nature Nanotechnology".

Tue, 24 Oct 2017 14:14:00 +0200
Boltzmann Lecture - Lisa Randall: The Nature of Dark Matter https://cms.univie.ac.at//news/news-detailansicht/article/boltzmann-lecture-lisa-randall-the-nature-of-dark-matter/?tx_ttnews%5BbackPid%5D=110280&cHash=c159def69ee8907d4b176a08f716df27 Professor Lisa Randall (Harvard University) will discuss possibilities for dark matter, focusing on... Short Biography

Professor Lisa Randall studied theoretical particle physics and cosmology at Harvard University. Her research connects theoretical insights addressing puzzles in our understanding of the properties of matter, the universe, and space. Randall has developed and studied a wide variety of ideas that could take us beyond our current understanding of particle physics and cosmology, the most prominent involving extra dimensions of space. Randall’s current research focus is dark matter and her latest book, /Dark Matter and the Dinosaurs, /is asweeping overview of the evolution of the Universe, the Milky Way, the Solar System, and life. Randall’s books, /Warped Passages/ (2005), and /Knocking on Heaven’s Door/ (2011), were featured on the New York Times’ lists of “100 Notable Books.” Her e-book, /Higgs Discovery: The Power of Empty Space/, was published in 2012.

Professor Randall’s studies have made her among the most cited and influential theoretical physicists. In 2016, she received the Julius Wess Prize, from the Karlsruhe Institute of Technology. In 2013, she received the Andrew Gemant Award from the American Institute of Physics and in 2007 she received the Julius Lilienfeld Prize from the American Physical Society for her work on elementary particle physics and cosmology and for communicating this work to the public. Professor Randall was on the list of Time Magazine's "100 Most Influential People" of 2007 and was one of 40 people featured in The Rolling Stone 40th Anniversary issue that year and was featured in Newsweek's "Who's Next in 2006" as "one of the most promising theoretical physicists of her generation" and in Seed Magazine's "2005 Year in Science Icons.

Professor Randall earned her PhD from Harvard University and held professorships at MIT and Princeton University before returning to Harvard in 2001. Randall is a member of the National Academy of Sciences, the American Philosophical Society, the American Academy of Arts and Sciences, was a fellow of the American Physical Society, and is a past winner of an Alfred P. Sloan Foundation Research Fellowship, a National Science Foundation Young Investigator Award, and a DOE Outstanding Junior Investigator Award. She is an Honorary Member of the Royal Irish Academy and an Honorary Fellow of the British Institute of Physics. She is also the recipient of honorary degrees from Brown University, Duke University, Bard College, and the University of Antwerp.


Thu, 19 Oct 2017 15:00:00 +0200
Gregor Leuthner and Maximilian Liebetreu receive prestigious uni:docs Fellowships 2017 https://cms.univie.ac.at//news/news-detailansicht/article/gregor-leuthner-and-maximilian-liebetreu-receive-prestigious-unidocs-fellowships-2017/?tx_ttnews%5BbackPid%5D=110280&cHash=3c3900ac2bca11d4f52be070efa79301 At the Faculty of Physics we welcome Gregor Leuthner (Physics of Nanostructured Materials) and... Gregor Thomas Leuthner will conduct his research on "Spatially Localized Chemistry in the Electron Microscope" in the research group "Physics of Nanostructured Materials" under the supervision of Jani Kotakoski. Before working on his master project "Electron Beam Induced Chemical Etching at Graphene Edges" with Jani Kotakoski he was involved in electron microscopy and data analysis which lead to a co-authorship of the article "Isotope analysis in the transmission electron microscope" by T. Susi et al published in "Nature Communications" in 2016.

Maximilian Liebetreu will study the "Influence of Polymer Topology on Polymer Rheology" in the research team headed by Christos Likos of the "Computational Physics" group. In 2017, he presented the results of his master thesis "Conformations and dynamics of polymers of different topologies under shear" supervised by Christos Likos at the "DPG Spring Meeting" (Dresden, Germany) and the international conference "Liquids" (Ljubljana, Slovenia).

Uni:docs Research Project "Spatially Localized Chemistry in the Electron Microscope" - Gregor Thomas Leuthner
Two-dimensional (2D) materials have gained much attention in research and media in the recent years. They consist only of one or a few atomic layers (like graphene or molybdenum disulfide, MoS2, respectively) leading to interesting properties through the confinement of the electronic wavefunctions. Due to the promising properties, these materials have been proposed for many applications. Since most material properties can be modified by defects, defect-engineering is of high importance for tailoring the 2D materials specifically, e.g., for next generation integrated circuits or ultimately thin membranes for filtration and sensing applications.
One of the most important characterization methods for 2D materials is transmission electron microscopy (TEM), in which energetic electrons are used to form an image of the atomic structure. However, the electrons can also damage the specimen. When properly understood, this effect may be used for defect-engineering.
Currently, especially chemical processes that occur during TEM investigations are not fully utilized, because they have not been studied in detail. In this project, using the unique experimental equipment (Nion UltraSTEM100 modified specifically to allow non-standard in situ experimentation) available at the University of Vienna, I will focus specifically on this topic by controlling the gas pressure and composition in the sample chamber while exposing only one atom at a time to the electron irradiation.
With the available setup, I can control the gas composition in the column via a leak valve system over a range of pressures ranging from ultra high vacuum to values four orders of magnitude higher (1e-10 - 1e-6 mbar) during imaging. After improving the understanding of the role of the chemical composition of the atmosphere during electron irradiation on the atomic structure of 2D materials, I will focus on utilizing this knowledge to establish efficient ways to defect-engineer them for future applications.

Uni:docs Research Project "Influence of Polymer Topology on Polymer Rheology"- Maximilian Liebetreu
Understanding polymer dynamics and topological effects on rheological properties has been an increasingly important topic in computational soft matter research in recent years. Studies on knotted ring polymers, characteristics of polymer melts and polymers under confinement have all been performed before, but the effects of hydrodynamics and shear on such systems remain unclear.
We present three sub-projects to shed more light on the influence of planar Couette flow on a variety of systems. This research project is purely computational and employs a variety of different simulation techniques.
The first sub-project builds on my Master's thesis' results on 31-knots under shear. We will extend these studies to other topological states such as 41- and 51-knots to check for common behavior. We will also study tumblingand tank-treading frequencies in the presence of a knot.
The second sub-project builds on studies suggesting shear thinning for polymer suspensions. For a concentrated solution of semiflexible ring polymers, stacking is known to occur. We will compute the system's viscosity and check whether stacking is still observable under shear. Recent experimental evidence predicts strong influence of the cutting of some of the rings on the system's viscosity, so we aim at reproducing and quantifying this behavior. The third sub-project deals with ultrasoft disc-shaped nanoparticles, which are known to exhibit a densityinduced anchoring transition under confinement. We will study the influence of increasing Weissenberg number on anchoring.
Each sub-part of the Doctoral thesis investigation is connected to each other via a hierarchy of complexity (from single molecule to collective behavior to confined geometries) as well as by the use of related methods, hoping to gain novel insights into the role of topological constraints on flow behavior of macromolecules.

Information for potential applicants to the uni:docs fellowship programme:
The uni:docs fellowship programme offers individual scholarships for highly qualified doctoral candidates at the University of Vienna. On the following days, info-sessions for applicants will take place:

  • 27 November 2017, 15:00-17:00 (in German)
  • 28 November 2017, 10:00-12:00 (in English)

Registration: please send an email to event.doktorat@univie.ac.at
Location: Center for Doctoral Studies, Berggasse 7, 1090 Vienna, seminar room 2

Thu, 19 Oct 2017 13:28:00 +0200
Nobel Prize in Physics 2017: The observation of gravitational waves https://cms.univie.ac.at//news/news-detailansicht/article/nobel-prize-in-physics-2017-the-observation-of-gravitational-waves/?tx_ttnews%5BbackPid%5D=110280&cHash=2557294caa01f134da7b1f7b52a76b3b The Nobel Prize in Physics 2017 was awarded to Rainer Weiss, Barry C. Barish and Kip S. Thorne for... uni:view: Mister Chruściel, what is your reaction to the Nobel Prize in physics awarded to the three scientists Rainer Weiss, Barry C. Barish and Kip S. Thorne?
Piotr Chruściel: I cannot think of a Nobel Prize in physics more deserved than this one. The direct observation of gravitational waves provides the most beautiful confirmation so far of Einstein's theory of general relativity. The discovery is a monument to Einstein, to the power of the human brain, to our ingenuity in pushing technology to unprecedented limits: the precision required in the measurement of the gravitational waves is identical to that needed to detect the change of distance of Saturn from our sun by the diameter of a hydrogen atom.

When Einstein discovered that his theory predicts gravitational waves, he calculated their intensity and wrote that we will never be able to measure them. Well, the Laser Interferometric Gravitational Observatory (LIGO) did it. And without Barish, Thorne, and Weiss, there would have never been a LIGO.

uni:view: What is the scientific significance of the research of Rainer Weiss, Barry C. Barish und Kip S. Thorne – and the importance for humans?
Chruściel: Detection of gravitational waves will not affect our everyday life in a foreseeable future. This is similar to most results in basic science, which provide the background for our understanding of the world. One can think here of foundations of a house: they are rarely seen, but houses without foundations will topple before long.

Did the discovery of the Higgs boson, a few years back, change our life? It did not, but without it we wouldn't be sure that the standard model of particle physics is correct.

We have been confident, since the late 1980's, that gravitational waves exist. The Nobel Prize in 1993 has been awarded to Hulse and Taylor, the discoverers of a pulsar whose motion was witness to existence of waves as predicted by Einstein's theory of gravitation.  This gave us an indirect confirmation, now we have a direct one.

But this is only the tip of the iceberg. The first detection provided us with three new black holes for the price of one: two black holes before merger, and a post-collision one. The masses of these black holes, about 30 and 35 solar masses before the collision, and about 60 solar masses for the final black hole, were larger than any other stellar-size black holes observed, and predicted to exist. The subsequent observations of black hole collisions (and we have four up-to-date) confirmed the existence of many such black holes. This is a revolution in astrophysics, where we can now observe the sky using gravitational waves, and see things that are undreamed-of with optical or X-ray astronomy. And we are discovering new objects in the sky as we go.

There is of course the vertiginous question, are there limits to our understanding of nature, of physics, of the universe? The LIGO detections are pushing the boundaries of human vanity further than ever.

uni:view: Have there been – former – scientists of the University of Vienna involved?
Chruściel: LIGO has two faces. The first one is the instruments themselves, which provide the data. The second is the LIGO Consortium, consisting of about 1.000 scientists worldwide, whose task is to analyze the data. University of Vienna has indirect ties to the Consortium, through former students: Sacha Husa, a PhD graduate from University of Vienna and currently Professor at the Universitat de les Illes Balears, has helped to develop numerical tools needed to analyze and interpret the huge stream of data flowing out of the LIGO detectors.

Similarly for Michael Puerrer, who is currently working at the Albert Einstein Institute for Gravitational Physics in Potsdam. We are further very happy that another of our students, Patricia Schmidt, currently at Radboud University in Nijmegen, has actively participated in the analysis of the LIGO data. Sascha, Michael and Patricia are co-authors of the landmark papers announcing and describing all four gravitational wave detections so far.

In this context one should not forget about Sir Hermann Bondi, born in Vienna in 1919, who passed away in 2005 after an illustrious scientific career amongst the spires of Cambridge Colleges. He is widely recognized as the researcher who set the ground for the theoretical understanding of gravitational radiation, and would have been one of the recipients of the prize if still alive.

YouTube "LIGO"

uni:view: You yourself are an expert in the field of Gravitational waves. What does this Nobel Prize mean for your own research?
Chruściel: General relativity (GR) is a demanding subject, drawing on all of physics, and on many mathematical tools. As a consequence, not many physicists have a working knowledge of the field, and therefore the GR community is (relatively) small. LIGO and other GR achievements (e.g., the discovery of the accelerated expansion of the universe) are arousing interest in the field, and so one can hope for more academic positions for young colleagues interested in GR.

I was very pleased to see last year the doubling of the number of students attending my lectures on general relativity. This was without doubt related to the LIGO observations. There is clearly a need amongst students to be introduced to the field, and I together with the members of my group will be happy to provide. Needless to say, the associated teaching load further increases the pressure on the number of academic jobs.

Big science needs big funding, and the LIGO observations should bring new financial life to projects such as the Einstein telescope, a proposed third-generation ground-based gravitational wave detector, currently under study, which will push further the detectability limits for the waves. Similarly we hope that the plans to build a new detector in Australia will be revived. A new detector in Australia will increase dramatically our ability to localize the origin of the signals.

uni:view: What are the differences and the similarities of your personal research from those of the Nobelprize winners?
Chruściel: The strength of the Vienna gravitational physics group is, and always was, the mathematical aspects of Einstein's theory of relativity. I and my colleagues, Peter Aichelburg, Bobby Beig, Walter Simon from the Physics department, or Michael Eichmair  from the Department of Mathematics, to name a few, have clarified many aspects of black holes, gravitational waves, general relativistic stars, energy in general relativity, or the behaviour of gravitational fields in various regimes. These are paper-and-pencil studies, which provide solid mathematical foundations to experiments such as LIGO. But we stay away from the tremendous experimental efforts involved in setting-up the experiments, and running them, or the incredibly sophisticated numerical simulations needed to analyze and interpret the stream of data pouring-out of the detectors.

The University of Vienna has a contribution to future gravitational wave detectors through the discovery of new mirror coatings by Markus Aspelmeyer and his group. These low-noise reflective coatings will be used in the next upgrade of the LIGO instruments.

uni:view: What will the future hold in this field?
Chruściel: The LIGO and VIRGO instruments are there, new instruments are being built, and all those will be observing the sky for years to come. A satellite mission, the Laser Interferometric Space Antena, which will be observing gravitational waves in a different frequency band, is being prepared for launch by the European Space Agency. We have to be able to develop methods to analyze and interpret the resulting streams of data faster and better than what we can do today.

On the theory side, many mathematical aspects of gravitational waves beg further understanding. A seemingly simple question, such as stability of black holes under small perturbation, has been occupying tens of mathematical relativists for years, with a proof remaining elusive. Questions such as the change of gravitational wave forms under small changes of initial configurations of the gravitating systems are mathematical terra incognita, and need to be answered to obtain a satisfactory understanding of sources of gravitational waves.

I could add many further problems to the above, so please rest reassured that both experimentalists and mathematical relativists will have plenty to do in the coming years.

Last, but not least, astrophysicists have  to explain now how black holes of 35 solar masses came to life. This is not an easy task within the existing scenarios of stellar evolution, which did not anticipate such a possibility.

uni:view: Thank you for the interview! (red)

Since April 2010, Piotr Chruściel holds the professorship for Gravitational Physics at the Faculty of Physics. Prior to his affiliation with the University of Vienna he carried out research and taught in renowned institutions such as the University of Oxford and the Max Planck Institute for Gravitational Physics. (Photo: MFO)




Thu, 05 Oct 2017 09:12:00 +0200
Polaron Bricklayers at Work on Surfaces https://cms.univie.ac.at//news/news-detailansicht/article/polaron-bricklayers-at-work-on-surfaces/?tx_ttnews%5BbackPid%5D=110280&cHash=27f9f791ebd43d439e131c600e38d87f A joint theoretical and experimental work led by the University of Vienna (Computational Materials... When a crystal is cleaved, a new surface forms that interrupts the regular distribution of ions within the material. The breaking of surface bonds and the alteration of interatomic forces increase the surface stress and reduce the stability of the fresh surface. To overcome this instability, the majority of surfaces undergo a spontaneous geometrical reconstruction, which is generally associated with charge transfer between surface atoms. Unraveling the mechanism responsible for such reconstructions is essential to understanding properties of surfaces, and it helps optimize materials performance in applications such as microelectronics and fuel cells. By combining first principles calculations (University of Vienna, group Cesare Franchini) and surface sensitive experiments (TU Wien, group Ulrike Diebold), an alternative and radically different mechanism for surface reconstructions was found based on charge trapping.

Polarons play a pivotal role in this process. These quasiparticles, which form via the coupling between excess charges and the lattice phonon field, are ubiquitous in polar semiconductors such as oxides. We studied an archetypal polaron material, rutile titanium dioxide, and varied the polaron density at the surface by introducing an increasing number of surface oxygen vacancies. Owing to the repulsive interaction between the polarons, the surface free energy increases until, at a critical amount, the surface transforms.

This polaron-mediated mechanism is likely to be a pervasive phenomenon that could explain structural, electronic, and magnetic reconstructions at surfaces and interfaces of ionic materials. Besides the fundamental interest, surface polarons could be employed to tune surface properties, control surface geometries, and provide a way to facilitate charge transfer in catalytic processes.

Michele Reticcioli, Martin Setvin, Xianfeng Hao, Peter Flauger, Georg Kresse, Michael Schmid, Ulrike Diebold, and Cesare Franchini, "Polaron-Driven Surface Reconstructions",

Phys. Rev. X 7, 031053 (2017)

DOI: doi.org/10.1103/PhysRevX.7.031053

Tue, 03 Oct 2017 13:12:00 +0200