No. I/11 - 31 March 2011
PSI photon, neutron and muon user facilities newsletter
An important milestone for the realization of the new SwissFEL facility was reached on the 24th of August 2010, when the core of the new facility, the 250 MeV injector, was set into operation at the Paul Scherrer Institute. This part will be used to develop and test new schemes in accelerator physics as well as diagnostics and undulators. The SwissFEL facility is expected to start user operation in 2017. It is already evident that the experiments performed at FLASH (Hamburg) and LCLS (Stanford) will enable discoveries in many areas of current research that cannot be obtained using existing methods.
Rafael Abela on behalf of the PSI SwissFEL team
Research highlightsObservation of a ubiquitous three-dimensional superconducting gap function in optimally doped Ba0.6K0.4Fe2As2
Y-M. Xu et al, Nature Physics 7, 198 (2011)
The iron-pnictide superconductors have a layered structure formed 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. Read the full story
G. Schwarz et al, Journal of the American Chemical Society 133, 547 (2011)
Self-assembly of Fe2+ ions and the rigid ditopic ligand 1,4-bis(2,2′:6′,2′′-terpyridin-4′-yl)benzene results in metallo-supramolecular coordination polyelectrolytes (MEPE). Sequential self-assembly of MEPE and dialkyl phosphoric acid esters of varying chain length via electrostatic interactions leads to the corresponding polyelectrolyte−amphiphile complexes (PAC), which have liquid−crystalline properties. The PACs have a stratified architecture where the MEPE is embedded in between the amphiphile layers. Upon heating above room temperature, the PACs show either a reversible or an irreversible spin-crossover (SCO) in a temperature range from 360 to 460 K depending on the architecture of the amphiphilic matrix. As the number of amphiphiles per metal ion is increased in the sequence 1:2, 1:4, and 1:6, the temperature of the SCO is shifted to higher values whereas the amphiphile chain length does not have a significant impact on the SCO temperature. In summary, we describe in this article how the structure and the magnetic response function of PACs can be tailored through the design of the ligand and the composition. To investigate the structure and the magnetic behavior, we use X-ray scattering, X-ray absorption spectroscopy, differential scanning calorimetry, faraday-balance, and superconducting quantum interference measurements in combination with molecular modeling.
Read the full story
Z. Shermadini et al, Physical Review Letters 106, 117602 (2011)
Muon-spin rotation and relaxation (μSR), electrical resistivity, magnetization and differential scanning calorimetry measurements performed on a high-quality single crystal of Cs0.8(FeSe0.98)2 are reported. Whereas the transport and magnetization data confirm the bulk character of the superconducting state below Tc=29.6(2) K, the μSR data indicate that the system is magnetic below TN=478.5(3) K, where a first-order transition occurs. The first-order character of the magnetic transition is confirmed by differential scanning calorimetry data. Taken all together, these data indicate in Cs0.8(FeSe0.98)2 a microscopic coexistence between the superconducting phase and a strong magnetic phase. The observed TN is the highest reported to date for a magnetic superconductor.
Read the full story
PSI Summer School on Condensed Matter ResearchPSI Summer School 2011.
New calls for proposalsSLS: PX-beamlines
deadline: June 15, 2011
deadline: September 15, 2011
deadline: May 15, 2011.
SµS/instruments GPS, LTF, and GPD
deadline: June 2011
An overview about all proposal submission deadlines of the PSI facilities can be obtained here.
Upcoming events18-21 April 2011, Advances in X-ray Free-Electron Lasers: Radiation Schemes, X-ray Optics and Instrumentation" part of the SPIE 2011 Optics and Optoelectronics Symposium, Prague, Czech Republic. More information
13-22 August 2011, 10th PSI summer school on condensed matter research: phase transitions
Zug, Switzerland. Early registration is open. More information
15-16 September 2011, 2nd Joint Users' Meeting at PSI: JUM@P'11
PSI Villigen, Switzerland. Registration is open. More information
Please have a look at the full conference calendar
Facility newsSLS: Materials science beamline upgrade
The MS beamline actually undergoes a comprehensive upgrade. In addition to providing fundamental improvements to both powder and SXRD experiments, the upgrade should allow new experimental setups previously excluded to the beamline. The beamline should be ready for user operation beginning 2012.
SINQ: New option on AMOR reflectometer
The SELENE option on the reflectometer AMOR passed its first test with an exchangeable elliptical guide, allowing measurements on small samples, in the time-of-flight mode, to be improved by approximately one order of magnitude. More information: Nucl Instr Meth A 634, S12 (2011).
SµS: Successful test of the new high field magnet
In February 2011 the 9.5 Tesla superconducting magnet for the new high field spectrometer has been delivered and successfully tested at PSI. This constitutes a key milestone in the completion of the high priority project of the µSR facility. In addition, all essential parts of the spectrometer are currently under construction.
New low temperature capabilities at Dolly
Recently, first µSR experiments have been performed at Dolly down to 300 mK by using a 3He (Heliox) stick inserted in the existing 4He Variox cryostat. Furthermore first cryogenic tests have been done with a dilution fridge (Kelvinox) insert which in the future will allow to perform µSR measurements at temperatures down to 50 mK at Dolly.