Scientific Highlights 2005-2011

22. December 2011

A close look at correlated electrons in heavy-fermion metal through ARPES

Showing astonishing properties like magnetism, superconductivity, Kondo and heavy-fermion (HF) behavior, rare-earth intermetallic compounds have been at the forefront of modern solid state physics for many years. Most of these properties are related to a delicate interplay between the partially filled 4f-shell and conduction electrons. Studying HF system YbRh2Si2 we made the observation of crystal-electric field (CEF) splittings of a 4f state by means of k-resolved photoemission. Their interaction with extended valence bands can force the localized CEF-split 4f states to become dispersive and induce Fermi level crossings in specific parts of the k-space. This can change the ground-state symmetry as well as the occupancy, number, energy separation, energy order and degeneration of the CEF-split magnetic 4f states k-dependently, i.e. very different from the widely believed scenario based on non-interacting atomic-like 4f orbitals. We got direct access to the Fermi surface of this system and: (i) detected its strong f-character, (ii) disentangled its topology and features reflecting f-d coupling at the surface and bulk of the material, (iii) explored evolution of the iso-energy surfaces closely below the Fermi energy that indeed change dramatically at the meV range.
Facility: SLS
Reference
Insight into the f-Derived Fermi Surface of the Heavy-Fermion Compound YbRh2Si2
S. Danzenbächer et. al.
Phys. Rev. Lett. 107, 267601 (2011) / DOI: 10.1103/PhysRevLett.107.267601

k Dependence of the Crystal-Field Splittings of 4f States in Rare-Earth Systems
D. V. Vyalikh et. al.
Phys. Rev. Lett. 105 237601 (2010) / DOI: 10.1103/PhysRevLett.105.237601
Contact
Dr. Luc Patthey
Swiss Light Source at Paul Scherrer Institut
Phone: +41 56 310 4562
Email: luc.patthey@psi.ch


Dr. Ming Shi
Swiss Light Source at Paul Scherrer Institut
Phone: +41 56 310 2393
Email: ming.shi@psi.ch

18. November 2011

New insights into the cell’s protein factory

Eukaryotic ribosomes are among the most complex cellular machineries of the cell. These large macromolecular assemblies are responsible for the production of all proteins and are thus of pivotal importance to all forms of life. Two independent research groups at the ETH Zürich and the Institute of Genetics and Molecular and Cellular Biology in Strasbourg have obtained new insights into the atomic structure of the eukaryotic ribosome. The results have been published in the journal Science. All diffraction data were measured with synchrotron light at the Swiss Light Source macromolecular crystallography beamline X06SA at the Paul Scherrer Institute.

Read the full story
Facility: SLS
Reference
Crystal structure of the eukaryotic 60S ribosomal subunit in complex with initiation factor 6
Klinge S, Voigts-Hoffmann F, Leibundgut M, Arpagaus S, Ban N.
Science Vol. 334 (6058), 2011 / DOI: 10.1126/science.1211204

The Structure of the Eukaryotic Ribosome at 3.0 A Resolution
Ben-Shem A, Garreau de Loubresse N, Melnikov S, Jenner L, Yusupova G, Yusupov M.
Science 2011 Nov 17 Epub
Contact
Dr. Vincent Olieric
Swiss Light Source at Paul Scherrer Institut
Phone: +41 56 310 5233
Email: vincent.olieric@psi.ch


Dr. Meitian Wang
Swiss Light Source at Paul Scherrer Institut
Phone: +41 56 310 4175
Email: meitian.wang@psi.ch

9. November 2011

Bilayer manganites reveal polarons in the midst of a metallic breakdown

The origin of colossal magnetoresistance (CMR) in manganese oxides is among the most challenging problems in condensed- matter physics today. The true nature of the low-temperature electronic phase of these materials is heavily debated. By combining photoemission and tunnelling data, we show that in the archetypal bilayer system La2-2xSr1+2xMn2O7, polaronic degrees of freedom win out across the CMR region of the phase diagram. This means that the generic ground state of bilayer manganites supports a vanishing coherent quasi-particle spectral weight at the Fermi level throughout k-space. The incoherence of the charge carriers, resulting from strong electron–lattice interactions and the accompanying orbital physics, offers a unifying explanation for the anomalous charge-carrier dynamics seen in transport, optics and electron spectroscopies. The stacking number N is the key factor for true metallic behaviour, as an intergrowth-driven breakdown of the polaronic domination to give a metal possessing a traditional Fermi surface is seen in this system.

Facility: SLS
Reference
Bilayer manganites reveal polarons in the midst of a metallic breakdown
F. Massee, S. de Jong, Y. Huang, W. K. Siu, I. Santoso, A. Mans, A. T. Boothroyd, D. Prabhakaran, R. Follath, A. Varykhalov, L. Patthey, M. Shi, J. B. Goedkoop & M. S. Golden
Nature Physics (2011)
Published online 11 September 2011
DOI: http://dx.doi.org/10.1038/nphys2089
Contact
Dr. Ming Shi and Dr. Luc Patthey
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Email: ming.shi@psi.ch / luc.patthey@psi.ch


22. July 2011

Investigation of a new method for the diagnosis of cancer in breast tissue

Collaboration between research, hospital and industry aimed at transferring innovative procedure into daily practice.
The Paul Scherrer Institute (PSI) has developed a new breast cancer diagnostic method, and is now carrying out first tests on non-preserved human tissue in conjunction with the Kantonsspital Baden AG. This new method should be able to reveal structures that cannot be seen using conventional mammography. Standard procedures only determine the extent to which X-rays are attenuated by various tissue structures. In contrast to this, the new method also makes use of the fact that X-rays actually consist of waves, and that their properties change slightly as they travel through tissue. These changes are now measurable and can contribute to the creation of a more meaningful image of the object under investigation. Scientists from the research department at Philips are currently investigating the use of this process as the basis for application in medical practice, and in mammography in particular. The researchers have reported on their results in the online edition of the Investigative Radiology journal.
The aim of any mammography investigation is to detect tumours in the female breast as early as possible, so that treatment can start in good time. A good mammography procedure is therefore expected to recognise as many tissue changes as possible and to distinguish tumour tissue clearly from any other tissue. At the same time, the radiation dose administered during the investigation must be kept as low as possible.

Read the full story
Facility: SLS
Reference
The First Analysis and Clinical Evaluation of Native Breast Tissue Using Differential Phase-Contrast Mammography
Stampanoni, Marco; Wang, Zhentian; Thüring, Thomas; David, Christian; Roessl, Ewald; Trippel, Mafalda; Kubik-Huch, Rahel A.; Singer, Gad; Hohl, Michael K.; Hauser, Nik
Investigative Radiology; published online 22 July 2011
DOI: 10.1097/RLI.0b013e31822a585f
Contact
Prof. Dr. Marco Stampanoni, Institute for Biomedical Engineering at ETH Zurich and the Laboratory for Macromolecules and Bioimaging at the Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
Tel: +41 56 310 4724, +41 79 292 34 47; E-mail: marco.stampanoni@psi.ch
Dr. Nik Hauser, Chief Medical Officer at the Women’s Clinic, Certified Breast Centre, Kantonsspital Baden AG, CH-5404 Baden, Switzerland
Tel: +41 56 486 3636; E-mail: nik.hauser@ksb.ch

6. May 2011

Observation of Orbital Currents in CuO

Although high-temperature (Tc) superconductivity was discovered in the cuprates 25 years ago, there is still no consensus on its microscopic origin.
The peculiar properties of the normal state are widely thought to hold the key to understanding the electronic behavior of the cuprates, including superconductivity. For this reason considerable attention has been paid to the pseudo-gap region of the phase diagram. One basic and interesting theoretical approach to describe the pseudo-gap phase predicts the existence of time-reversal symmetry breaking because of orbital currents. However, experimental verification of symmetry-breaking by orbital currents in cuprates is very difficult. So far there is indirect evidence, which is strongly debated. We have performed soft X-ray resonant diffraction with polarization analysis, a technique pioneered at the Swiss Light Source, on cupric oxide (CuO) to study orbital currents. We have been able to unambiguously observe orbital currents in a copper-oxygen plaquette, the building block of high-temperature cuprates.
The recorded diffracted intensities from our sample have a complex dependence on the X-ray polarization that can be explained only by the presence of an ordered (antiferro-type) pattern of orbital currents between the copper and the oxygen atoms.
Our observations provides strong encouragement for models based on orbital current ordering and related phenomena in high-temperature superconductors.
Facility: SLS
Reference
Observation of Orbital Currents in CuO V. Scagnoli, U. Staub, Y. Bodenthin, R. A. de Souza, M. García-Fernández, M. Garganourakis, A. T. Boothroyd, D. Prabhakaran, S. W. Lovesey
Science 332, 696 (2011)
DOI: 10.1126/science.1201061
Contact
Dr. Valerio Scagnoli
Paul Scherrer Institut
Tel: +41(0)56 310 5366, E-Mail: valerio.scagnoli@psi.ch [English, Italian]

Dr. Urs Staub
Paul Scherrer Institut
Tel: +41(0)56 310 4494, E-Mail: urs.staub@psi.ch [German, English]

13. April 2011

X-ray methods help to understand brain disorders better

An international team of researchers from Denmark, Germany, Switzerland and France has developed a new method for making detailed X-ray images of brain tissue, which has been used to make the myelin sheaths of nerve fibres visible. Damage to these protective sheaths can lead to various disorders, such as multiple sclerosis. The facility for creating these images of the protective sheaths of nerve cells is being operated at the Swiss Light Source (SLS), at the Paul Scherrer Institute. The research team has reported on its work in the online version of the scientific journal NeuroImage.

Read the full story
Facility: SLS
Reference
Molecular X-ray computed tomography of myelin in a rat brain
T.H. Jensen, M. Bech, O. Bunk, A. Menzel, A. Bouchet, G. Le Duc, R. Feidenhans'l, F. Pfeiffer
NeuroImage, 2011;
DOI: 10.1016/j.neuroimage.2011.04.013
Contact
Dr. Oliver Bunk
Paul Scherrer Institut
Phone: (+41) 56 310 3077, E-mail: oliver.bunk@psi.ch

18. January 2011

LaAlO3 - Buckling under pressure to hand over the charges

In this paper, we report on the change in the atomic structure of the conducting interface between the insulators LaAlO3 and SrTiO3 as a function of the LaAlO3 layer thickness. We discovered that the atoms at the interface buckle in an attempt to counteract the internal electric field produced when these two insulators touch one another. Despite the partial neutralizing effect of the buckling, the electrical potential becomes sufficiently high above a critical thickness to pull electrons out of the LaAlO3 and provide the conducting layer. The electric field then collapses and the buckling is suppressed. These findings, made possible using x-ray scattering techniques capable of identifying atomic positions down to one millionth of one millionth of a meter, explain at a structural level the discoveries of the conductivity at the interface in 2004 and the need for a minimum LaAlO3 thickness to induce it, in 2006. This phenomenon may have important technological applications in future nanoscale electronics based on metal-oxides."

Reference
Facility: SLS
Reference
S. A. Pauli, S. J. Leake, B. Delley, M. Björck, C. W. Schneider, C. M. Schlepütz, D. Martoccia, S. Paetel, J. Mannhart, and P. R. Willmott, Phys. Rev. Lett. 106, 036101 (2011).
Contact
Prof. Dr. P.R. Willmott and S.A. Pauli
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Email: philip.willmott@psi.ch & stephan.pauli@psi.ch

16. January 2011

Observation of a ubiquitous three-dimensional superconducting gap function in optimally doped Ba0.6K0.4Fe2As2

The iron-pnictide superconductors have a layered structureformed by stacks of FeAs planes from which the superconductivity originates. Given the multiband and quasi three-dimensional1 (3D) electronic structure of these high-temperature superconductors, knowledge of the quasi-3D superconducting (SC) gap is essential for understanding the superconducting mechanism. By using the kz capability of angle-resolved photoemission, we completely determined the SC gap on all five Fermi surfaces (FSs) in three dimensions on Ba0.6K0.4Fe2As2 samples. We found a marked kz dispersion of the SC gap, which can derive only from interlayer pairing. Remarkably, the SC energy gaps can be described by a single 3D gap function with two energy scales characterizing the strengths of intralayer Δ1 and interlayer Δ2 pairing. The anisotropy ratio Δ12, determined from the gap function, is close to the c-axis anisotropy ratio of the magnetic exchange coupling Ja/Jab in the parent compound2. The ubiquitous gap function for all the 3D FSs reveals that pairing is short-ranged and strongly constrains the possible pairing force in the pnictides. A suitable candidate could arise from short-range antiferromagnetic fluctuations.

Reference
Facility: SLS
Reference
Y-M. Xu, Y-B. Huang, X-Y. Cui, E. Razzoli, M. Radovic, M. Shi, G-F. Chen, P. Zheng, N-L. Wang, C-L. Zhang, P-C. Dai, J-P. Hu, Z. Wang & H. Ding, Nature Physics 7, 198 (2011), doi:10.1038/nphys1879
Contact
Dr. Ming Shi
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Email: ming.shi@psi.ch

26. November 2010

Röntgenpreis for X-Ray research goes to Christian David

On 26th November 2010, Christian David, scientist at the Laboratory for Micro and Nanotechnology, received the Röntgenpreis for research in radiation science. David pioneered a method to enhance the quality of X-ray images. He received the award jointly with Franz Pfeiffer from Technische Universität München who worked closely together with him.

The award
The Röntgen Prize is awarded annually by the University of Giessen (Germany) for new and outstanding scientific work in fundamental research in the fields of radiation physics or radiation biology. The award is named after Wilhelm Conrad Röntgen, the physicist who discovered X-rays and was a professor at Giessen during the period 1879–1888. The award was established jointly by the Pfeiffer Vacuum GmbH company and the Dr. Erich Pfeiffer-Stiftung and Ludwig-Schunk-Stiftung e.V. foundations.

Read full article
Laboratory: LMN
Contact
Dr. Christian David
Laboratory for Micro and Nanotechnology, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Email: christian.david@psi.ch

25. October 2010

Direct Determination of Large Spin-Torque Nonadiabaticity in Vortex Core Dynamics

We use a pump-probe photoemission electron microscopy technique to image the displacement of vortex cores in Permalloy discs due to the spin-torque effect during current pulse injection. Exploiting the distinctly different symmetries of the spin torques and the Oersted-field torque with respect to the vortex spin structure we determine the torques unambiguously, and we quantify the amplitude of the strongly debated nonadiabatic spin torque. The nonadiabaticity parameter is found to be β = 0:15 +/- 0:07, which is more than an order of magnitude larger than the damping constant α, pointing to strong nonadiabatic transport across the high magnetization gradient vortex spin structures.

Read the viewpoint "the alphabet of spin in nanostructures" by Rolf Allenspach and Philipp Eib
Facility: SLS
Reference
L. Heyne, J. Rhensius, D. Ilgaz, A. Bisig, U. Rüdiger, M. Kläui, L. Joly, F. Nolting, L. J. Heyderman, J. U. Thiele and F., Kronast, Phys. Rev. Lett. 105, 187203 (2010).
Contact
Prof. Dr. Klaeui Mathias , Prof. Dr. Frithjof Nolting, Dr. L. J. Heyderman
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Email: mathias.klaeui@psi.ch, frithjof.nolting@psi.ch, laura.heyderman@psi.ch

17. October 2010

Moving Monopoles Caught on Camera - researchers make visible the movement of monopoles in an assembly of nanomagnets

For decades, researchers have been searching for magnetic monopoles; isolated magnetic charges, which can move around freely in the same way as electrical charges – since magnetic poles normally only occur in pairs. Now a team of researchers at the Paul Scherrer Institute PSI in Switzerland and University College Dublin have managed to create monpoles in the form of quasiparticles in an assembly of nanoscale magnets and to observe how they move using a microscope at the Swiss Light Source (SLS) to make the magnetic structures visible. As with the elementary monopoles, which were first predicted by the british physicist Paul Dirac in 1931, each monopole is connected by a string to a monopole of opposite charge. The two monopoles can nevertheless move independently of each other. These results are not only of scientific interest, but could also provide a basis for the development of future electronic devices. These results will be published online in Nature Physics on 17 October.

Read full article
Laboratory: LMN
Reference
Elena Mengotti, Laura J. Heyderman, Arantxa Fraile Rodríguez, Frithjof Nolting, Remo V. Hügli, and Hans-Benjamin Braun, Real space observation of emergent magnetic monopoles and associated Dirac strings in artificial kagome spin ice. Nature Physics Advance Online Publication 17 October 2010; DOI: 10.1038/NPHYS1794
Contact
Dr. Laura J. Heyderman
Laboratory for Micro and Nanotechnology, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Email: laura.heyderman@psi.ch

23. September 2010

High-resolution method for computed nano-tomography developed

A novel nano-tomography method developed by a team of researchers from the Technische Universität München (TUM), the Paul Scherrer Institute (PSI) and the ETH Zurich opens the door to computed tomography examinations of minute structures at nanometer resolutions. The new method makes possible, for example, three-dimensional internal imaging of fragile bone structures. The first nano-CT images generated with this procedure was published in the renowned journal Nature on September 23, 2010. This new technique will facilitate advances in both life sciences and materials sciences.

Read full article
Facility: SLS
Reference
Martin Dierolf, Andreas Menzel, Pierre Thibault, Philipp Schneider, Cameron M. Kewish, Roger Wepf, Oliver Bunk, Franz Pfeiffer: “Ptychographic X-Ray Computed Tomography at the Nano-Scale”. Nature, September 23, 2010 – DOI: 10.1038/nature09419
Contact
Dr. Oliver Bunk
Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Email: oliver.bunk@psi.ch

27. July 2010

Understanding plastic semiconductors better

New method allows important insights into polymer semiconductors

Semiconductors made from polymer materials are becoming increasingly important for the electronics industry – as a basis for transistors, solar cells or LEDs – showing important advantages when compared to conventional materials: they are lightweight, flexible and very cheap to produce. Usually, they consist of more than one substance as they get their particular electric properties only when several materials are blended. But in order to find the optimal material, one has to know how different polymers mix together (or don’t) and how the various components contribute to the properties of the material. Researchers from the Paul Scherrer Institute (Switzerland) and the University of Cambridge (United Kingdom) have developed a method that allows them to determine the detailed structure of the material – both in the bulk and on the surface. The investigations were performed at the Swiss Light Source SLS of the Paul Scherrer Institute.

Read full article
Facility: SLS
Reference
Benjamin Watts, Christopher R. Mc Neill, Macromolecular Rapid Communications, 2010, DOI: 10.1002/marc.201000269
Contact
Dr. Benjamin Watts
Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Email: benjamin.watts@psi.ch

19. July 2010

New X-ray technique distinguishes between that which previously looked the same

A new method forms the basis for the widespread use of an X-ray technique which distinguishing types of tissue that normally appear the same in conventional X-ray images

Traditional X-ray images can clearly distinguish between bones and soft tissue, with muscles, cartilage, tendons and soft-tissue tumours all look virtually identical. The phase-contrast technique developed a few years ago at the Paul Scherrer Institute enables X-ray images to be produced that clearly distinguish between these tissue types. Researchers at the Paul Scherrer Institute and the Chinese Academy of Science have now further developed the technique to such an extent that, in the future, it will be as simple to use as conventional X-rays. They anticipate that the process will help tumours to be detected in medical practices and could also help identify hazardous objects in luggage at airports. The researchers are reporting their findings this week in the online edition of the Proceedings of the National Academy of Sciences of the United States of America (PNAS).

Read full article
Facility: SLS
Reference
Peiping Zhu, Kai Zhang, Zhili Wang, Yinjin Liu, Xiaosong Liu, Ziyu Wu, Samuel A. McDonald, Federica Marone, and Marco Stampanoni, PNAS Early Edition, 19 July 2010
Contact
Prof. Dr. Marco Stampanoni
Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Email: marco.stampanoni@psi.ch

22. November 2009

Observation of a d-wave nodal liquid in highly underdoped Bi2Sr2CaCu2O8+δ

A key question in condensed-matter physics is to understand how high-temperature superconductivity emerges on adding mobile charged carriers to an antiferromagnetic Mott insulator. We address this question using angle-resolved photoemission spectroscopy to probe the electronic excitations of the non-superconducting state that exists between the Mott insulator and the d-wave superconductor in Bi2Sr2CaCu2O8+δ. Despite a temperature-dependent resistivity characteristic of an insulator, the excitations in this intermediate state have a highly anisotropic energy gap that vanishes at four points in momentum space. This nodal-liquid state has the same gap structure as that of the d-wave superconductor but no sharp quasiparticle peaks. We observe a smooth evolution of the excitation spectrum, along with the appearance of coherent quasiparticles, as one goes through the insulator-tosuperconductor transition as a function of doping. Our results suggest that high-temperature superconductivity emerges when quantum phase coherence is established in a nonsuperconducting nodal liquid.

Read full article
Facility: SLS
Reference
U. Chatterjee, M. Shi, D. Ai, J. Zhao, A. Kanigel, S. Rosenkranz, H. Raffy, Z. Z. Li,
K. Kadowaki, D. G. Hinks, Z. J. Xu, J. S.Wen, G. Gu, C. T. Lin, H. Claus, M. R. Norman,
M. Randeria and J. C. Campuzano, Nature Physics 6, 99-103 (22 November 2009)
Contact
Dr. Ming Shi (ming.shi@psi.ch)
Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
Publication: http://www.nature.com/nphys/journal/v6/n2/full/nphys1456.html

9. October 2009

Watching atoms move: an ultrafast phase transition

One approach to advance our understanding of the complex interactions between different degrees of freedom in strongly correlated systems is to use time-resolved methods to study the response of a material after it has been driven out of equilibrium. Ultrafast optical techniques have demonstrated considerable potential to unravel the correlations that drive the interesting physics in such materials. Phonon dynamics in these studies are only indirectly observed via the electronic response, and are not generally able to unambiguously disentangle the dynamics of the lattice from those of the electronic subsystem. By using femtosecond x-ray diffraction to probe directly the structural response of photoexcited manganite, we have found evidence of an ultrafast laser-induced structural phase transition driven directly by electronic excitation and occuring on a sub-picosecond time scale.

Read full article
Facility: SLS
Reference
P. Beaud, S.L. Johnson, E. Vorobeva, U. Staub, R. A. De Souza, C.J. Milne, Q.X. Jia, G. Ingold, Phys. Rev. Lett. 103, 155702 (2009)
Contact
Paul Beaud
Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Email: paul.beaud@psi.ch

6. June 2009

Confinement-Induced Orientational Alignment of Quasi-2D Fluids

Extreme confinement is known to induce ordering of the fluid, thereby affecting its properties. However, experimental studies are hampered by the confining surfaces. In this work we show that x-ray scattering experiments on artificial fluids under extreme confinement, making use of colloidal fluids confined in diffraction gratings, can be used to determine both the average density profile and the fluid's local structure. In particular, the experiment shows how extreme confinement induces orientational alignment of the fluid, while still preserving a fluid-like structure.

Read full article
Facility: SLS
Reference
P.K. Nygård, D. K. Satapathy, J. Buitenhuis, E. Perret, O. Bunk, C. David, J. F. van der Veen, EPL 86, 66001 (2009), DOI: 10.1209/0295-5075/86/66001
Contact
Dr. Kim Nygard (kim.nygard@psi.ch)
Prof. Dr. J. Friso van der Veen (friso.vanderveen@psi.ch)
Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland

2. June 2009

Advanced phase contrast imaging using a grating interferometer

Conventional absorption based X-ray microtomography can become limited for objects showing only very weak attenuation contrast at high energies. However, a wide range of samples studied in biology and materials science can produce significant phase shifts of the X-ray beam and thus phase contrast X-ray imaging can provide substantially increased contrast sensitivity. A Differential Phase Contrast (DPC) imaging facility, based on grating interferometry, has been installed at the TOMCAT beamline, with the aim of having a high-throughput of samples in terms of fast data acquisition and post-processing. We have made hardware and software advancements to enable a range of PEC tomographic imaging methods to be applied, such as local and 'widefield' PEC tomography. Darkfield imaging, based on the mechanism of small-angle scattering, provides simultaneous and complementary information about a sample at the micron and the sub-micron length scales. The technique allows the visualisation of the soft tissue features of a rat brain, for example, with a contrast impossible to obtain with conventional absorption-based imaging.

Read full article
Facility: SLS
Reference
S. A. McDonald, F. Marone, C. Hintermüller, G. Mikuljan, C. David, F. Pfeiffer and M. Stampanoni, J. Synchrotron Rad. 16, 562-572 (2009).
Contact
Marco Stampanoni
Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Email: marco.stampanoni@psi.ch

2. May 2009

Electrons with opposite spins move in opposite directions

In one dimension, there are only two ways to move: left or right. This leads to some peculiar properties for one-dimensional systems on the atomic scale. In our paper we present a one-dimensional conductor forming on a bismuth surface, which effectively separates the electrons going through it according to their spin, a kind of rotation around the electron's axis. It turns out that electrons going to the left have exactly the opposite spin as electrons going to the right. Such a situation could have useful applications in the field of spintronics, a novel type of electronics which is based on the electron's spin rather than its charge and which could lead to more effective computers or even quantum computing. The state reported here is in several ways similar to so-called edge states appearing in the recently discovered quantum spin Hall effect but instead of being found for a sandwich structure of semiconductors at very low temperatures, it is found on a simple, clean surface, is truly one-dimensional and, most remarkably, even exists at room temperature.

Read full article
Facility: SLS
Reference
J.W. Wells et. al., Phys. Rev. Lett. 102, 096802 (2009)
Contact
J.H. Dil
Paul Scherrer Institut, Research Division Synchrotron Radiation and Nanotechnology,
5232 Villigen PSI, Switzerland,
Email: jan-hugo.dil@psi.ch

27. April 2009

Putting the squeeze on phonons

Photon squeezing has been the subject of intense interest in the field of quantum optics, since it serves as a unique demonstration of the quantum nature of light. On a practical level, squeezing offers opportunities to make interferometric measurements much more precise than would normally be allowed by quantum uncertainty limits. In principle, the physics of squeezing may be applied to many different types of bosons. Our work demonstrates phonon squeezing by using femtosecond laser excitation of bismuth to create squeezed phonon states and then femtosecond x-ray diffraction to watch how the atomic position variance in the crystal evolves in time.

Read full article
Facility: SLS
Reference
S. L. Johnson, P. Beaud, E. Vorobeva, C. J. Milne, E. D. Murray, S. Fahy, and G. Ingold, Phys. Rev. Lett. 102, 175503 (2009)

See accompanying Viewpoint commentary Physics 2, 33 (2009)
Contacts
S. L. Johnson
Paul Scherrer Institut, Research Division Synchrotron Radiation and Nanotechnology,
5232 Villigen PSI, Switzerland,
Email: steve.johnson@psi.ch


15. April 2009

A fast selenium derivatization strategy for crystallization and phasing of nucleic acid structures

The growing number of biologically important nucleic acid sequences (DNA and RNA) demands a fast and reliable method for their de novo three-dimensional structure determination. In this work, we described a fast and inexpensive strategy for the crystallization and phasing of structures of nucleic acid and nucleic acid/protein complexes.

In the early 1990's, covalent modification of nucleic acid using Selenium was introduced as a new approach to facilitate crystal structure determination of nucleic acid (in case of failure of classical molecular replacement or heavy atoms derivatives techniques, such modification allows to use the powerful multiwavelength anomalous dispersion technique to tackle the phase problem). Hovewer, due to a cumbersome and expensive synthesis of such Seleno-labeled nucleic acid, only few structures have been determined.

We have developed an efficient strategy for crystallization and structure determination of nucleic acids by exploiting the similar crystallization properties of 2'-SeCH3- and 2'-OCH3-modification.

Read full article
Facility: SLS
Reference
Vincent Olieric, Ulrike Rieder, Kathrin Lang, Alexander Serganov, Clemens Schulze-Briese,
Ronald Micura Philippe Dumas and Eric Ennifar, RNA, 2009 Apr;15(4):707-15 (2009)
Faculty of 1000 recommended article
Contact
Vincent Olieric Paul Scherrer Institut, Research Division Synchrotron Radiation and Nanotechnology,
5232 Villigen PSI, Switzerland,
Email: vincent.olieric@psi.ch

5. March 2009

Exciting Heavy Metal

Retrieving Structures in Photocatalysis Photocatalysts play an important role in a broad range of applications, from photochemical conversion of light energy into chemical energy through to initiating novel chemical reactions. One family of compounds that has attracted much attention is the dinuclear d8-d8 platinum, rhodium and iridium complexes that have a highly reactive electronic excited state. When photo-excited with light these systems have been shown to abstract H-atoms from a variety of substrates and initiate electron transfer processes. In this work we exam-ine the structure of the triplet excited state of a diplatinum member of this photocatalyst family.

Read full article
Facility: SLS
Reference
Structural Determination of a Photochemically Active Diplatinum Molecule by Time-Resolved EXAFS Spectroscopy , by R. M. van der Veen at al. Angew. Chem. Int. Ed. (in press, 2009).
Contacts
R.M. van der Veen
Paul Scherrer Institut, Research Division Synchrotron Radiation and Nanotechnology,
5232 Villigen PSI, Switzerland,
Email: renske.vanderveen@psi.ch
Prof. Dr. Majed Chergui, EPFL,
Email: majed.chergui@epfl.ch

3. October 2008

Building blocks of an artificial kagome spin ice: Photoemission electron microscopy of arrays of ferromagnetic islands

Arrays of dipolar coupled ferromagnetic islands arranged in specific geometries provide ideal systems to directly study frustration. We have examined with photoemission electron microscopy the magnetic configurations in three basic building blocks of an artificial kagome spin ice consisting of one, two, and three rings. The kagome spin ice arrangement is particularly interesting because it is highly frustrated and the three interactions at a vertex are equivalent. Employing dipolar energy calculations, we are able to make a full characterization of the magnetic states and therefore identify the lowest energy states. Experimentally we find that the ice rule is always obeyed even at low dipolar coupling strengths. However, as the number of rings increases there is a drastic decrease in the ability to achieve the low-energy states via demagnetization, a behavior also identified in the magnetization reversal. This carries the implication that the ground state will never be achieved in the infinite system. Finally, we show that at low coupling, the applied field direction governs the resulting states. This work opens the door to a novel class of systems for future spintronic applications.

Read full article
Facility: SLS
Reference
Building blocks of an artificial kagome spin ice: Photoemission electron microscopy of arrays of ferromagnetic islands, by E. Mengotti et al., PhysRevB,78 144402 (2008).
Contacts
E. Mengotti
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland,
Email: elena.mengotti
Dr. Laura Heiderman, Research Group Leader
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Email: laura.heyderman

18. July 2008

Super-Resolution X-ray Microscopy unveils the buried secrets of the nanoworld

A novel super-resolution X-ray microscope developed by a team of researchers from the Paul Scherrer Institut (PSI) and EPFL in Switzerland combines the high penetration power of x-rays with high spatial resolution, making it possible for the first time to shed light on the detailed interior composition of semiconductor devices and cellular structures. The first super-resolution images from this novel microscope will be published online July 18, 2008 in the journal Science. “Researchers have been working on such super-resolution microscopy concepts for electrons and x-rays for many years,” says EPFL Professor and team leader Franz Pfeiffer. “Only the construction of a dedicated multi-million Swiss-franc instrument at PSI's Swiss Light Source allowed us to achieve the stability that is necessary to implement our novel method in practice.”

Read full article
Facility: SLS
Reference
High-Resolution Scanning X-Ray Diffraction Microscopy, by P. Thibault et al., Science, Vol 321 (2008).
Contacts
Dr. Pierre Thibault, Postdoctoral Researcher
Paul Scherrer Institut, 5232 Villigen PSI, Switzerland,
Email: pierre.thibault@psi.ch
Prof. Dr. Franz Pfeiffer, Research Group Leader
Paul Scherrer Institut & EPFL, 5232 Villigen PSI, Switzerland
Email: franz.pfeiffer@epfl.ch

17. April 2008

Coherent Diffraction Imaging Using Phase Front Modifications

We introduce a coherent diffractive imaging technique that utilizes multiple exposures with modifications to the phase profile of the transmitted wave front to compensate for the missing phase information. This is a single spot technique sensitive to both the transmission and phase shift through the sample. Along with the details of the method, we present results from the first proof of principle experiment. The experiment was performed with 6.0 keV X-rays, in which an estimated spatial resolution of 200 nm was achieved.

Read full article
Facility: SLS

Coherent Diffractive Imaging Using Phase Front Modifications, I. Johnson*, K. Jefimovs, O. Bunk, C. David, M. Dierolf, J. Gray, D. Renker, and F. Pfeiffer Physical Review Letters 100, 155503 (2008) http://link.aps.org/abstract/PRL/v100/e155503 (17.04.2008) * To whom correspondence should be addressed: ian.johnson@psi.ch

20. January 2008

X-ray dark-field imaging using a grating interferometer

A type of X-ray imaging that shows detail otherwise lost, and which is compatible with conventional radiography instrumentation is now feasible, reports a study published online in Nature Materials. This technique offers unprecedented resolution for several applications, including medical imaging, security screening and industrial non-destructive testing.

Dark-field imaging is commonly used in visible light microscopy, and it enables details to be resolved that are otherwise smeared out in the direct reflection mode or bright field. The quality of the dark-field image depends on the intensity of the light scattered by the object. With X-rays, however it has always been difficult to have a high enough signal-to-noise ratio, and therefore the use of X-ray dark-field imaging has usually been restricted to very-high-intensity light sources, such as synchrotrons.

In a collaborating research team led by Franz Pfeiffer (Laboratory for Synchrotron Radiation) and Christian David (Laboratory for Micro-and Nanotechnology) has shown that by using an appropriate arrangement of certain optical components it is possible to obtain a high signal-to-noise ratio even with conventional X-ray tubes, as they demonstrate by revealing the very fine structure of bones in a chicken wing.

Read full article
Facility: SLS

Hard-X-ray dark-field imaging using a grating interferometer, Franz Pfeiffer* , Martin Bech, Oliver Bunk, Philipp Kraft, Eric F. Eikenberry, Christian Brönnimann, Christian Grünzweig and Christian David, Nature Materials , 174801 (2007) AOP: http://dx.doi.org/10.1038/nmat2096 (20.01.2008)

26. October 2007

Pushing atoms on a swing

The typical time scale of atomic motion during fundamental physical processes such as phase transitions in solids or molecular dynamics in chemical reactions ranges from ten to hundreds of femtoseconds. The direct observation of these processes on an atomic length scale therefore requires utrashort light pulses at wavelengths capable of resolving the underlying atomic structures. For these reason significant efforts have been undertaken in the past decades to develop femtosecond sources operating in the hard x-ray spectral domain. At the Swiss Light Source we have recently commissioned an undulator source offering spatially and temporally stable x-ray pulses of ~100 fs duration that are tunable in the angstrom range. The temporal characteristics of the x-ray pulses are determined studying high-amplitude phonon dynamics of photo-excited bismuth. Optical control of real space atomic motion is successfully demonstrated.

Read full article
Facility: SLS

Spatiotemporal Stability of a Femtosecond Hard–X-Ray Undulator Source Studied by Control of Coherent Optical Phonons, P. Beaud S. L. Johnson, A. Streun, R. Abela, D. Abramsohn, D. Grolimund, F. Krasniqi, T. Schmidt, V. Schlott, and G. Ingold,, Phys. Rev. Lett. 99, 174801 (2007) DOI: 10.1103/PhysRevLett.99.174801

9. October 2007

The conducting meat in the insulating sandwich

In 2004, it was discovered that when a layer of LaAlO3 (LAO) is in contact with a layer of SrTiO3 (STO), an ultrathin layer of highly conducting material is formed where they contact one another, despite the fact that both LAO and STO are insulators. The underlying physics responsible for this phenomenon is still much disputed, despite a worldwide concerted research drive since then to explain it. Using x-rays, the atomic structure of the interface between LAO and STO has been revealed. For the first time, the exact positions and chemical compositions of each atomic layer were defined. Using simple arguments regarding electrostatic energy minimization and the known sizes of the contributing ions, it was shown that the conducting layer consists of about three monolayers of a graded mixture of STO and LAO, which is predicted to be conducting. Thus this fascinating and potentially technologically important phenomenon could be explained based on structural arguments alone.

Read full article
Facility: SLS

Structural Basis for the Conducting Interface between LaAlO3 and SrTiO3, P.R. Willmott et al., Phys. Rev. Lett. 98, 155502 (2007) DOI: 10.1103/PhysRevLett.99.155502

4. October 2007

The exciting story of TiSe2

In this story of TiSe2, experiment and theory meet to provide an explanation for a long-standing enigma. In this system, the electrons rearrange themselves spontaneously at low temperature, resulting in a new periodicity from that of the original lattice. This phase change is driven by a decrease in the total energy of the system. However, the nature of this transition has been a matter of controversy for a long time. Recently, physicists from Neuchâtel rejuvenated an old theory to explain their photoemission data taken at the SLS on TiSe2 and to provide a promising solution to this problem.

Read full article
Facility: SLS

Evidence for an Excitonic Insulator Phase in 1T-TiSe2, H. Cercellier, C. Monney, F. Clerc, C. Battaglia, L. Despont, M. G. Garnier, H. Beck, P. Aebi*, Luc Patthey, H. Berger and L. Forró , Phys. Rev. Lett. 99, 146403 (2007)

3. October 2007

Is Smaller Stronger?

In 2004 researcher discovered that a single crystalline metal is stronger when the sample volume is reduced to the micron or even submicron range. In an ongoing debate on the origin of this phenomenon classical deformation theories are questioned. The suspicion that structural defects, i.e. deviations from perfect crystalline structure would play an important role in the smaller is stronger effect, could not be verified because of the lack of an appropriate measuring technique. In “Time resolved Laue diffraction of deforming micro pillars” the microstructure of micron sized Au pillars is followed in real time using a micro focused white X-ray beam at the microXAS beamline of the Swiss Light Source. This newly developed technique demonstrates the occurrence of crystal rotation and shows that the increased strength of the smallest Au pillars can be explained by plasticity starting on a slip system that is geometrically not predicted, but selected because of the character of the preexisting defect structure. Time resolved Laue diffraction presents itself as a powerful technique to investigate the fundamentals of the “smaller is stronger” paradigm.

Read full article
Facility: SLS

Time-Resolved Laue Diffraction of Deforming Micropillars2, Robert Maaß, Steven Van Petegem, Helena Van Swygenhoven, Peter M. Derlet, Cynthia A. Volkert and, Daniel Grolimund Phys. Rev. Lett., 99, 145505 (2007) doi: 10.1103/PhysRevLett.99.145505

8. March 2007

Making the invisible visible

Using x-rays scientists have learned to make the invisible visible. Since almost 100 years doctors use the difference in x-ray absorption between bones and tissue to diagonose their patients. Using modern synchrotrons it has become possible to do such imaging with much reduced side effects. The new phase contrast method uses the fact that, like visible light, x-rays are deflected when traveling through objects with different densities. This allows making small density variations visible even in weakly absorbing tissue. This novel technology may now find broad applications outside of synchrotrons. Using a specially designed grating interferometer such phase contrast imaging can now be done with ordinary x-ray tubes. The technique was first tested on an insect, but after further tests and development it may well be used for human patients. Here it may soon make invisible tumors visible and allow early therapy.

Read full article
Facility: SLS

Hard x-ray phase tomography with low-brilliance sources, F. Pfeiffer, O. Bunk, C. Kottler, and C. David, Phys. Rev. Lett. 98, 108105 (2007) DOI: 10.1103/PhysRevLett.98.108105

1. March 2007

A virus in a nutshell

Nature has found remarkable ways to protect sensitive objects. One example is the seed of a nut which is protected by its shell. Another are viruses from the cypovirus family. They are hidden inside tiny natural crystals where they can survive harsh conditions until they meet their target, the gut of the silkworm. Here the virus is released from the crystal causing a virus infection of the worm. Researchers have now unraveled the structure of these natural protein crystals. This allows them to understand how and why the virus particles are so well protected by its crystal. This knowledge might not only help farmers by protecting the silkworm from the cypovirus family, much more it may lead to novel concepts for dedicated drug delivery. Imagine a beneficial drug introduced into such a crystal designed to specifically delivery its cargo to a target, the center of a disease in the human body.

Read full article
Facility: SLS

The molecular organization of cypovirus polyhedra Fasseli Coulibaly, Elaine Chiu, Keiko Ikeda, Sascha Gutmann, Peter W. Haebel, Clemens Schulze-Briese, Hajime Mori, and Peter Metcalf* Nature, 446, 97 (1 March 2007)

29. September 2006

A microscope without a lens

It is known since a long time that x-rays, which are nothing but light of very short wave length, can be used for microscopy. This is particularly attractive because due to the small wave length x-rays allow studying objects which are invisibly small in an optical microscope. Here we present a truly new kind of x-ray microscope, one which does not need lenses and can nevertheless investigate objects of arbitrary size. This so called ptychographic microscope needs coherent (laser-like) x-rays from a defined source and produces an interference pattern on a CCD camera. Translating the sample and then stitching together many such interference patterns allows to easily reconstruct the object which produced the diffraction pattern. Although similar techniques were known, this technique is new since it needs no lens, can image objects which attenuate the x-rays and shift their phase, and can image arbitrarily large objects. Furthermore the reconstruction in the computer is significantly faster, simple and unambiguous. A real breakthrough in microscopy accomplished without using a single lens.

Read full article
Facility: SLS

Hard X-ray lensless imaging of extended objects J. M. Rodenburg, A. C. Hurst, A. G. Cullis, B.R. Dobson, F. Pfeiffer, O. Bunk, C. David, K. Jefimovs, and I. Johnson. Phys. Rev. Lett. 98, 034801 (2007)

10. August 2006

Looking inside fossilised embryos

Although only recently discovered, the fossil record of embryonic development has already begun to challenge cherished hypotheses on the origin of major animal groups. Synchrotron-based X-ray Tomographic Microscopy has provided unparalleled insight into the anatomy and preservation of these fossil remains and this has allowed us to test competing hypotheses on their nature. With knowledge of both adults and embryos from the time of diversification of the major animals groups, it is now possible to test models of developmental evolution based on modern model organisms using information from their long-extinct ancestors.

Read full article
Facility: SLS

Synchrotron X-ray tomographic microscopy of fossil embryos Philip C. J. Donoghue, et al. Nature 442, 680-683 (10 August 2006)

2. June 2006

Phase Imaging with Neutrons

Neutrons are usually considered as small massive particles with a size of about 10^-15 meters. Due to the wave-particle duality of quantum mechanics, however, they can equivalently be considered as matter wave packets whose spatial extent may be large enough to show interference effects similar to what can be observed with visible laser light. Measurements of the neutron wave packet's phase shift induced by different interactions with matter thus have a long and distinguished history in the exploration of the fundamental properties of quantum mechanics. Here we report how a setup consisting of three gratings can be used to produce images depicting the quantum-mechanical phase shifts of neutron wave packets induced by the influence of macroscopic objects. Applications aiming at the imaging of the magnetic domain structures inside macroscopic objects based on the neutrons interaction with the local magnetic field can be envisioned. Furthermore, this work could provide the basis for bridging the gap between imaging and quantum-optical investigations with other matter waves, such as protons, atoms, or molecules.

Read full article
Facility: SLS

Neutron phase imaging and tomography F. Pfeiffer, C. Grünzweig, O. Bunk, G. Frei, E. Lehmann, and C. David Phys. Rev. Lett. 96, 215505 (2006)

2. May 2006

How to avoid atomic sandpaper

When growing thin films of novel materials, smooth surfaces are a must. How else could one stack them layer by layer, as needed in optical coatings, sensors or conductors? One method known to produce atomically smooth films is Pulsed Laser Deposition (PLD). In PLD, a pulsed laser beam hits a bulk target. With every pulse, it creates a jet (or “plume”) of high energy atoms from the target. When these condense on a smooth substrate, they recreate the target material, but now as a thin film. Per laser pulse only about 1/100th of an atomic layer is deposited on the substrate. Although the fact that PLD produces atomically smooth films has long been known, the reasons for this were somewhat speculative. A recent experiment measured the roughness of PLD films, carefully adding one laser pulse after another. This provided the clue to the puzzle: when the first atoms land on the smooth substrate they form small islands of the material. Subsequent pulses lead either to formation of more small islands if the particles land on an uncovered part of the monolayer, or, importantly, cause already formed islands to break up if the energetic particles land on top of them. This avoids growth of "islands on top of islands", which would gradually result in rough films - that is, atomic sandpaper. Now that the process is understood, one can optimally tune PLD for growing thin films of materials which are then used in devices.

Read full article
Facility: SLS

Energetic smoothing studies of complex metal-oxide thin films P.R. Willmott, R. Herger, C.M. Schlepuetz, D. Martoccia, and B.D. Patterson, Phys. Rev. Lett. 96, 176102 (2006)

26. March 2006

Seeing ever finer Details with X-Rays

X-ray radiographic absorption imaging is an invaluable tool in medical diagnostics and materials science. For biological tissue samples, polymers, or fiber composites, however, the use of conventional X-ray radiography is limited due to their weak absorption. This is resolved at highly brilliant X-ray synchrotron or micro-focus sources by using phase-sensitive imaging methods to improve contrast. The requirements of the illuminating radiation mean, however, that hard x-ray phase-sensitive imaging has until now been impractical with more readily available x-ray sources, such as x-ray tubes. With the present work we show how a setup consisting of three transmission gratings can efficiently yield quantitative differential phase contrast images with conventional x-ray tubes. As opposed to existing techniques, the method requires no spatial or temporal coherence, is mechanically robust, and can be scaled up to large fields of view. The new method provides all the benefits of contrast enhanced phase-sensitive imaging, but yet is fully compatible with conventional absorption radiography. It is applicable to x-ray medical imaging, industrial non-destructive testing, and to other low-brilliance radiation, such as neutrons or atoms.

Read full article
Facility: SLS

Phase retrieval and differential phase-contrast imaging with low-brilliance X-ray source F. Pfeiffer, T. Weitkamp, O. Bunk, and C. David Nature Phys. 2, 258-261 (2006)

16. March 2006

Shining light on superconductors

More than 20 years ago researchers in Switzerland discovered that certain materials transport electrical current without any loss. For this they need to be cooled, but because they do so at relatively high temperatures (up to -150°C) they are called high temperature superconductors. How exactly the electrons transport current in such materials is still a mystery. But the electrons can be studied using the photoelectric effect where light of high energy knocks an electron out of the material. Measuring the electrons direction and energy provides the necessary information on the motion of the electron in the material. Combining experiments at the SLS and laboratory experiments, researchers now solved a longstanding puzzle. They show that the direction of electron motion is closely related to the arrangement of the atoms in the crystal. Even small distortions of the crystal symmetry are relevant and influence the electrons motion. The solved a long standing dispute about the origin of the so called shadow band. But the search is not over yet, identifying the mechanism leading to loss less currents in these materials needs more experiments. And as in the past synchrotron light will surely be part of this search.

Read full article
Facility: SLS

Experimental proof of a structural origin for the shadow Fermi surface of Bi2Sr2CaCu2O8+d A. Mans, I. Santoso, Y. Huang, W. K. Siu, S. Tavaddod, V. Arpiainen, M. Lindroos, H. Berger, V. N. Strocov, M. Shi, L. Patthey, and M. S. Golden Phys. Rev. Lett., 96, 107007 (2006)

31. October 2005

Magnets shine in a different color

Measuring -or feeling- magnetic interactions looks simple at first glance: holding two magnets close to each other gives an immediate idea. How about the case when the 'magnets of interest' are tiny and amount to nothing more than atoms? X-rays generated at the Swiss Light Source allow 'zooming in' on magnetic interactions relevant at inter-atomic scale: we bring forward the first evidence of local spin flips of atomic moments in a 'photon-in photon-out' scattering experiment.

Read full article
Facility: SLS
Localized Electronic Excitations in NiO Studied with Resonant Inelastic X-Ray Scattering at the Ni M Threshold: Evidence of Spin Flip S. G. Chiuzbãian et al. Phys. Rev. Lett. 95, 197402 (2005)

2. June 2005

Dance of the domains

In a ferromagnet regions exist where all the atoms orient their atomic compass neddles into one direction. These regions are called domains. A recent experiment succeeded in exciting such domains and watching their vibration and subsequent relaxation to the original state. This is the Dance of the domains. Such processes happen extremly fast, taking on the order of a few hundered picoseconds (ps), or half of a billionth of a second. The experiment showed that even in a structure as simple as a square there are three different excitations, which are associated with the domain, the walls seperating two domains and the vortex, created at the intersection of two domains. It was possible to analyze all of these processes quantitativly and determine the frequencies. Fortunately the frequencies are high, several GHz. The domains dance at a high beat, which is important in every day life, because these domains are used to store information on the hard-disk of your PC, and the faster the beat, the faster a PC can store data.

Read full article
Facility: SLS
Quantitative Analysis of Magnetic Excitations in Landau Flux-Closure Structures Using Synchrotron-Radiation Microscopy J. Raabe, C. Quitmann, C. H. Back, F. Nolting, S. Johnson, and C. Buehler Phys. Rev. Lett. 94, 217204 (2005)

1. April 2005

Controlling the ribosome

Ribosomes can be thought of as factories that build proteins from a set of genetic instructions. Translation relies on two selection processes: a) charging of tRNA by selection of the correct aminoacid to be covalently bound to it, b) the selection of the tRNA as specified by the codon of the mRNA. Aminoacyl-tRNA synthetases catalyse the first of these steps using hydrolysis of ATP. In the present study the ribosome of Thermus thermophilus was cocrystallised with initiator tRNAfMet and a structured mRNA fragment which codes for threonyl-tRNA synthetase. The thrS mRNA fragment consists of the translation operator domain flanked by two single stranded regions which constitute the ribosome binding site. Crystals containing functional ribosome in complex with initiator tRNAfMet and either thrS mRNA, mk27 mRNA from the bacteriophage T4, or in the absence of mRNA were obtained under similar experimental conditions. Highly complete and redundant data were collected from 300 to 5.5 Å at beamline X06SA. The electron densities derived from the diffraction images of the crystallised ribosome complexes suggest a general way in which mRNA control elements must be placed on the ribosome to perform their regulatory task.

Read full article
Facility: SLS
Translational Operator of mRNA on the Ribosome: How Repressor Proteins Exclude Ribosome Binding Lasse Jenner et al. Science Vol. 308. no. 5718, pp. 120 - 123