Scientific Highlights 2012

16. October 2012

X-rays provide insights into volcanic processes

Experiments performed at the Paul Scherrer Institute (PSI) investigate processes inside volcanic materials that determine whether a volcano will erupt violently or mildly.

In the experiments, an international team of scientists used a laser-based heating system to heat small pieces of volcanic material similarly to conditions present at the beginning of a volcanic eruption. They used X-rays from the Swiss Light Source (SLS) at the Paul Scherrer Institute (PSI) to observe, in real time, what happens to the rock as it goes from the solid to the molten state. A determining factor to the type of eruption that occurs is how fast gas bubbles form inside the material. These studies indicate that the type of eruption taking place may be established as early as the first few seconds of bubble growth. The researchers have published their results in the online journal Nature Communications.

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Reference
A 4D x-ray tomographic microscopy study of bubble growth in basaltic foam
Don R. Baker, Francesco Brun, Cedrick O'Shaughnessy, Lucia Mancini, Julie L. Fife, Mark Rivers
Nature Communications , 16 October 2012 DOI: 10.1038/ncomms2134
Contact
Don R. Baker, Earth and Planetary Sciences
McGill University, Montreal QC, H3A2A7, Canada
Phone: +1 514 398 7485; E-mail: don.baker@mcgill.ca

Julie L. Fife, Swiss Light Source
Paul Scherrer Institute, 5232 Villigen PSI, Switzerland,
Phone: +41 56 310 58 40; E-mail: julie.fife@psi.ch

2. September 2012

New Insights into Superconducting Materials

An American-Swiss research team has used a new X-ray technique at Swiss Light Source (SLS) of the Paul Scherrer Institute (PSI) to investigate the magnetic properties of atomically thin layers of a parent compound of a high-temperature superconductor. It turns out that the magnetic properties of such thin films differ by only a surprisingly small degree from those of macroscopically thick samples. In their experiment, the researchers investigated the material using X-ray light from the SLS and found out how the energy of the light changed as it passed through the sample. The “RIXS” technique that is available at PSI is the first of its kind that is sensitive enough to enable investigations on such thin films. At the present time, superconducting materials are already being studied by this technique. In the future, it could be used for studying the processes occurring in very thin superconductors and contribute to an understanding of the fascinating phenomenon of high-temperature superconductivity. The results of the present work have recently appeared in the journal Nature Materials.

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Contact
Dr. Thorsten Schmitt; Laboratory of Condensed Matter Physics, Research Division Synchrotron Radiation and Nanotechnology
Paul Scherrer Institut, 5232 Villigen PSI, Schweiz
Telephone: +41 56 310 37 62, E-mail: thorsten.schmitt@psi.ch
http://www.psi.ch/sls/adress/
Original publication
Spin excitations in a single La2CuO4 layer
M. P. M. Dean, R. S. Springell, C. Monney, K. J. Zhou, J. Pereiro, I. Božović, B. Dalla Piazza, H. M. Rønnow, E. Morenzoni, J. van den Brink, T. Schmitt & J. P. Hill
Nature Materials (2012); doi:10.1038/nmat3409; Published online 02 September 2012

20. August 2012

Three-Dimensional Electron Realm in Crystalline Solids Revealed with Soft-X-Rays

The electronic band structure E(k) as energy E of the electrons depending on its wavevector k is the cornerstone concept of the quantum solid state theory. The main experimental method to investigate E(k) is the angle-resolved photoelectron spectroscopy (ARPES). However, a small photoelectron escape depth of a few Å largely restricts the applications of ARPES to two-dimensonal crystals. A team of SLS scientists working at the ADRESS beamline have recently extended this technique to the much wider world of three-dimensional (3D) crystalline systems. They used soft-X-ray synchrotron radiation in the soft-X-ray photon energy range around 1 keV, where the photoelectron escape depth and concomitantly the 3D k-vector definition increase by a factor of 3-5. The problem of a dramatic loss of the photoexcitation cross-section by a few orders of magnitude in this energy range has been overpowered with ADRESS beamline, which delivers high photon flux exceeding that of the closest competitors by up to 2 orders of magnitude. The pilot soft-X-ray ARPES research has been carried out on the paradigm transition-metal-dichalcogenide VSe2. Unparalleled definition of the 3D k-vector has allowed the scientists to explore in 3D the Fermi surface of VSe2 determining the whole host of its unusual macroscopic properties including the electric conductivity anomalies. The textbook calrity of the experimental FS (figure) manifests excellent definition of the 3D k vector and regular photoexcitation matrix elements achieved at soft-X-ray energies. Autocorrelation analysis of 3D warping of the experimental Fermi surface has revealed its nesting as the precursor for the exotic 3D charge density waves in VSe2. This pilot research has been followed in the last year by a plethora of other breakthrough experiments exploiting the advantages of soft-X-ray ARPES on the probing depth and 3D k-vector definition, such as the electronic structure of Mn ferromagnetic impurities in the paradigm spintronic material GaMnAs, buried 2D electron gas in LaAlO3/SrTiO3 hererostructures, standing X ray waves excited ARPES of multilayer heterostructures allowing depth resolved electronic structure profiling, etc.

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Reference
Three-Dimensional Electron Realm in VSe2 by Soft-X-Ray Photoelectron Spectroscopy: Origin of Charge-Density Waves
V.N. Strocov, M. Shi, M. Kobayashi, C. Monney, X. Wang, J. Krempasky, T. Schmitt, L. Patthey, H. Berger and P. Blaha, Physical Review Letters 109 (2012) 086401
DOI: 10.1103/PhysRevLett.109.086401
Contact
Dr. Vladimir N. Strocov, Swiss Light Source
Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
Tel. +41 56 310 5311, email vladimir.strocov@psi.ch

12. July 2012

Ultra-short X-ray laser pulses precisely surveyed for the first time

X-ray lasers belong to a modern generation of light sources from which scientists in widely different disciplines expect to obtain new knowledge about the structure and function of materials at the atomic level. On the basis of this new knowledge, it could then be possible one day to develop better medicines, more powerful computers or more efficient catalysts for energy transformation. The scientific value of an X-ray laser stands or falls on the quality of the ultra-short X-ray pulses it produces and which researchers use to illuminate their samples. An international team led by scientists from the Paul Scherer Institute, PSI, has now precisely measured these pulses. In so doing, they have laid the foundation for a scientifically optimal utilisation of X-ray lasers – not least, of the planned SwissFEL at PSI. The results of this work have recently been published in the scientific journal Nature Communications.

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Reference
Exploring the wavefront of hard X-ray free electron laser radiation
Simon Rutishauser, Liubov Samoylova, Jacek Krzywinski, Oliver Bunk, Jan Grünert, Harald Sinn, Marco Cammarata, David M. Fritz, Christian David
Nature Communications: DOI: doi:10.1038/ncomms1950
Contact
Simon Rutishauser, Laboratory for Micro- and Nanotechnology
Paul Scherrer Institute, 5232 Villigen, Switzerland;
Telephone: +41 56 310 25 02, E-Mail: simon.rutishauser@psi.ch

Dr. Christian David, Group Leader X-ray optics and applications
Laboratory for Micro- and Technology
Paul Scherrer Institute, 5232 Villigen, Switzerland;
Telephone: +41 56 310 37 53, E-Mail: christian.david@psi.ch

3. July 2012

Controversy clarified: Why two insulators together can transport electricity

How can two materials which do not conduct electricity create an electrically conducting layer when they are joined together? Since this effect was discovered in 2004, researchers have developed various hypotheses to answer this question – each with its own advocates, who defend it and try to prove its validity. Now, an international team under the leadership of researchers at the Paul Scherrer Institute has probably settled the controversy. They have shown that it is the combination of the properties of both materials that produces the effect, and therefore disproved an alternative hypothesis, which proposes that the materials mix at the interface to create a new, conducting material. The materials under study are so-called perovskites, members of a large class of materials with interesting electrical or magnetic properties that could play a significant role in electronics and computing in the future. The results have been published in the scientific journal Nature Communications.

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Facility: SLS
Reference
Tunable conductivity threshold at polar oxide interfaces
M.L. Reinle-Schmitt, C. Cancellieri, D. Li, D. Fontaine, M. Medarde, E. Pomjakushina, C.W. Schneider,S. Gariglio, Ph. Ghosez, J.-M- Triscone, P.R. Willmott;
Nature Communications: DOI: 10.1038/ncomms1936
Contact
Prof. Philip Willmott, Laboratory for Synchrotron Radiation – Condensed Matter Physics;
Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
Phone: +41 56 310 51 26; E-mail: philip.willmott@psi.ch

Prof. Jean-Marc Triscone, DPMC, Université de Genève
24, quai Ernest-Ansermet, CH-1211 Genève 4
Phone: +41 22 379 66 55; E-mail: Jean-Marc.Triscone@unige.ch;

Prof. Philippe Ghosez, Université de Liège, Institut de Physique, B5a
Allée du 6 août, 17, B-4000 Sart Tilman, Belgium
Phone: +32 43 66 36 11; E-mail: Philippe.Ghosez@ulg.ac.be

30. April 2012

Three-Dimensional Spin Rotations in a Monolayer Electron System

In the emerging field of spintronics, the generation, injection, and in particular the control of highly spin polarized currents are main issues to be solved. Lifting of spin degeneracy by the spin-orbit interaction at surfaces, known as Rashba effect, represents a promising approach, since it generates two spin-polarized bands without the necessity of an external field. In our recent study, we realize such a system for a metallic surface layer on a semiconductor: Au/Ge(111). Based on a combination of spin-resolved photoemission with 3D detection and advanced density functional calculations, we have unveiled the complex spin texture at the Fermi surface. Due to the heavy atoms involved, this surface system shows a significant band splitting related to the spin-orbit interaction. Importantly, strong deviations from conventional Rashba physics occur. This pertains most prominently to a strong out-of-plane spin orientation. The spin pattern moreover shows in-plane rotations of the spin near mirror symmetry planes, which is observed for the first time. These findings pinpoint the complex spin texture found at surfaces, resulting from the potential landscape at the atomic scale. Interestingly, the spin texture bears close relationship to that predicted for the Fermi surface of topological insulators. Thus, these findings relate to a variety of topical solid-state issues, and could be stimulus for future studies of spin manipulation with regard to spintronics applications.

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Facility: SLS
Reference
Three-Dimensional Spin Rotations at the Fermi Surface of a Strongly Spin-Orbit Coupled Surface System
P. Höpfner, J. Schäfer, A. Fleszar, J. H. Dil, B. Slomski, F. Meier, C. Loho, C. Blumenstein, L. Patthey, W. Hanke, and R. Claessen
Phys. Rev. Lett. 108, 186801 (2012),DOI: 10.1103/PhysRevLett.108.186801
Contact
Dr. Jan Hugo Dil
Swiss Light Source at Paul Scherrer Institut
Phone: +41 56 310 5388
Email: jan-hugo.dil@psi.ch

18. April 2012

Physicists observe the splitting of an electron inside a solid

An electron has been observed to decay into two separate parts, each carrying a particular property of the electron: a spinon carrying its spin – the property making the electron behave as a tiny compass needle – and an orbiton carrying its orbital moment – which arises from the electron’s motion around the nucleus. These newly created particles, however, cannot leave the material in which they have been produced. This result is reported in a paper published in Nature by an international team of researchers led by experimental physicists from the Paul Scherrer Institute (Switzerland) and theoretical physicists from the IFW Dresden (Germany).

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Facility: SLS
Reference
Spin-Orbital Separation in the quasi 1D Mott-insulator Sr2CuO3
J. Schlappa, K. Wohlfeld, K. J. Zhou, M. Mourigal, M. W. Haverkort, V. N. Strocov, L. Hozoi, C. Monney, S. Nishimoto, S. Singh, A. Revcolevschi, J.-S. Caux, L. Patthey, H. M. Rønnow, J. van den Brink, and T. Schmitt;
Nature Advance Online Publication, 18.04.2012, DOI: 10.1038/nature10974
Contact
Dr. Thorsten Schmitt (experimentation)
Laboratory for Condensed Matter, Research Division Synchrotron Radiation and Nanotechnology,
Paul Scherrer Institute, 5232 Villigen PSI, Switzerland;
Tel: +41 56 310 37 62, E-Mail: thorsten.schmitt@psi.ch
http://www.psi.ch/sls/adress/

Prof. Dr. Jeroen van den Brink (theory)
Institute for Theoretical Solid State Physics,
IFW Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany;
Tel: +49/(0)351/4659-400, E-Mail: j.van.den.brink@ifw-dresden.de
http://www.ifw-dresden.de/institutes/itf/members/jvdb1

21. February 2012

Creating magnetism takes much longer than destroying it

Researchers at the Paul Scherrer Institute are finding out how long it takes to establish magnetism and how this happens. Establishing a magnetically ordered phase in the metallic alloy iron-rhodium takes much longer than the reverse process of demagnetization. This fact was established by researchers of the Paul Scherrer Institute (PSI), Switzerland, together with colleagues of an international collaboration. Magnetism is established in a two-step process. Initially, small magnetic regions form, but have random orientation. Subsequently, these regions rotate until they all have a common orientation. This is reported in an article which has recently been published in the renowned journal “Physical Review Letters”. The result comes from basic research, but has relevance for the computer industry, as it shows which processes limit the speed of magnetic data storage and where improvements might be made.

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Facility: SLS
Reference
Structural and Magnetic Dynamics of a Laser Induced Phase Transition in FeRh
S. O. Mariager, F. Pressacco, G. Ingold, A. Caviezel, E. Möhr-Vorobeva, P. Beaud, S. L. Johnson, C. J. Milne, E. Mancini, S. Moyerman, E. E. Fullerton, R. Feidenhans’l, C. H. Back, and C. Quitmann;
Phys. Rev. Lett. 108, 087201 (2012), DOI: 10.1103/PhysRevLett.108.087201
Contact
Dr. Christoph Quitmann
Swiss Light Source at Paul Scherrer Institut
Phone: +41 56 310 4560
Email: christoph.quitmann@psi.ch

24. January 2012

Origin of the Large Polarization in Multiferroic YMnO3 Thin Films

Multiferroic materials have attracted much interest because of their ability to control magnetism by the application of an electric field. This ability is expected to reduce the power required by electronic devices and to increase their speed. However, the number of multiferroic materials discovered so far has been small, and ferromagnetism and ferroelectricity in the known materials are often much weaker than required for practical applications. Hence, it is important to find novel multiferroic materials. In 2011, we succeeded in fabricating a YMnO3 multiferroic film having a dielectric polarization exceeding that of previous multiferroic thin films, and performed x-ray diffraction measurements to investigate the magnetic structure and lattice strain of this film. We discovered that the spin of Mn ions has two coexisting magnetic structures, namely the cycloidal and E-type antiferromagntic (AF) orderings, and that the lattice strain due to E-type AF orderings is the origin of the large electric polarization. The ability to produce multiferroic YMnO3 thin films and the understanding of the mechanism inducing the large electric polarization is expected to support the design of multiferroic materials for practical applications in the future.
Facility: SLS
Reference
Origin of the Large Polarization in Multiferroic YMnO3 Thin Films Revealed by Soft- and Hard-X-Ray Diffraction
H. Wadati et. al.
Phys. Rev. Lett. 108, 047203 (2012) / DOI: 10.1103/PhysRevLett.108.047203
Contact
Dr. Hiroki Wadati
Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo
Email: wadati@ap.t.u-tokyo.ac.jp

Dr. Urs Staub
Swiss Light Source at Paul Scherrer Institut
Phone: +41 56 310 4494
Email: urs.staub@psi.ch

18. January 2012

Liquids in narrow spaces

How does spatial confinement affect the microscopic structure of liquids?

This is a question which is receiving increasing attention from condensed matter physicists. Liquids are characterized by a short-ranged, so-called local structure, and it has been predicted theoretically about 25 years ago that confinement induces anisotropy in the local structure, and hence many properties, of liquids. However, this prediction had not been experimentally verified previously. Here, we have combined x-ray scattering experiments from colloid-filled nanofluidic channel arrays, a technique developed at PSI, with a state-of-the-art inhomogeneous liquid-state theory, to provide the first experimental verification of the theoretically predicted anisotropic local structure of confined liquids. The simultaneous experimental and theoretical description of confined liquids at this level allows accurate studies of the interaction mechanisms in liquids under spatial confinement.
Facility: SLS
Reference
Anisotropic Pair Correlations and Structure Factors of Confined Hard-Sphere Fluids: An Experimental and Theoretical Study
K. Nygard et al.
Phys Rev. Lett. 108, 037802 (2012) / DOI: 10.1103/PhysRevLett.108.037802
Contact
Dr. Kim Nygard
University of Gothenburg, Sweden
Email: kim.nygard@chem.gu.se

Prof. Dr. Friso van der Veen
Swiss Light Source at Paul Scherrer Institut
Phone: +41 56 310 5118
Email: friso.vanderveen@psi.ch