Transition énergétique

Ultracold neutrons (UCNs) are key for precision studies of fundamental parameters of the neutron and in searches for new charge-parity-violating processes or exotic interactions beyond the Standard Model of particle physics. The most prominent example is the search for a permanent electric-dipole moment of the neutron (nEDM). We have performed an experimental comparison of the leading UCN sources currently operating.

We employ time-resolved resonant x-ray diffraction to study the insulator-to-metal transition that is launched via resonant excitation of an infrared-active optical phonon mode in a half doped manganite. We find that the charge order reduces promptly with a highly nonlinear (quartic) dependence on excitation fluence.

Mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and its lanthanide ion (Ln³⁺) chelating phospholipid conjugate, 1,2-dimyristoyl-sn-glycero-3-phospho-ethanolamine-diethylene triaminepentaacetate (DMPE-DTPA), assemble into highly magnetically responsive polymolecular assemblies such as DMPC/DMPE-DTPA/Ln³⁺ (molar ratio 4:1:1) bicelles.

Dr. Marcin Gorzny, Post-Doc at LMN in the PSI career return program recieved a poster prize at the Swiss Nanoconvention 2017 for his contribution entitled: "Silicon chip as lipid membrane holder for serial crystallography experiments".

Despite remarkable progress in developing multifunctional materials, spin-driven ferro-electrics featuring both spontaneous magnetization and electric polarization are still rare. Among such ferromagnetic ferroelectrics are conical spin spiral magnets with a simultaneous reversal of magnetization and electric polarization that is still little understood. Such materials can feature various multiferroic domains that complicates their study.

Understanding the assembly of nanoparticles into superlattices with well-defined morphology and structure is technologically important but challenging as it requires novel combinations of in-situ methods with suitable spatial and temporal resolution.

Online combustion analysis relies heavily on spectral data to detect reactive intermediates isomer-selectively to establish e.g. kinetic flame models. Due to the difficulty to generate these species cleanly, spectral data are rather scarce. Here we report on the selective generation of three picolyl radical isomers (C₅H₄N-CH₂*) by deamination of aminomethylpyridines. Picolyl radicals are relevant in biofuel combustion, and could now be characterized by threshold photoelectron spectroscopy using synchrotron radiation. Vibrationally resolved bands and distinct ionization energies allow for isomer-specific detection of these elusive species in complex environments and permit us to explore new avenues in soot- and NOx formation kinetics.

Natural geological and engineered barriers play a key role in protecting the environment and the anthroposphere from the hazardous impact of deposited waste or spreading contaminants. Such natural geological and engineered barrier materials are commonly complex and heterogeneous. In-situ multimodal microscopic studies under conditions relevant to deep geological formations are crucial to identify the reactive components and reaction pathways or to validate proposed immobilization mechanisms. The present study demonstrated that a simplistic description by a sole reactive component is not an adequate representation of the geochemical reactivity responsible for the immobilization of plutonium within a natural Clay Rock barrier. Multimodal chemical imaging studies on intact, undisturbed systems are absolutely essential to ascertain the geochemical reactivity for relevant geochemical conditions and settings.

Free electron lasers (FELs) like SwissFEL help scientists to understand the mechanisms that switch properties of materials which are the basis for functions in electronics, solar cells, chemistry and biology. By using ultrashort X-ray pulses it becomes possible to visualize the ultrafast rearrangements of electrons and atoms that enable the properties to switch in molecules or crystals.

Free electron lasers (FELs) like SwissFEL help scientists to understand the mechanisms that switch properties of materials which are the basis for functions in electronics, solar cells, chemistry and biology. By using ultrashort X-ray pulses it becomes possible to visualize the ultrafast rearrangements of electrons and atoms that enable the properties to switch in molecules or crystals. An international consortium of researchers lead by Paul Scherrer Institute, Université de Rennes, and SLAC National Laboratory has now visualized the entire cascade of processes that lead to a change of the magnetic moment of electrons in a molecule within one trillionth of a second (10-12 s = 1 picosecond), using the FEL at Stanford, California (LCLS).

Metal nanostructures can be fabricated by irradiation of suitable metal organic precursor molecules with a focused X-ray beam. This novel techniques offer the advantage of energy-selective deposition by switching of the incident photon energy due to the non-linear photon absorption cross-section of the precursor molecules for resonant excitation.

Researchers from China and USA join forces with Swiss Light Source (SLS) macromolecular crystallography (MX) beamline scientists in a study, which aims at understanding an important step in the life cycle of the human betacoronavirus HKU1.

For decades, the mechanism of Mott phase in Ca₂RuO₄ has puzzled researchers. This material is a paradigmatic case of multi-band Mott physics including spin-orbit and Hund's coupling. Progress has been impeded by the lack of knowledge about the low-energy electronic structure. With our recent contribution, we provided-- using angle-resolved photoemission electron spectroscopy -- the band structure of the paramagnetic insulating phase of Ca₂RuO₄.

Spent fuel characterization is necessary to improve nuclear fuel design, optimize core refueling patterns and manage the handling, transport and storage of spent fuel assemblies. The experimental characterization of spent fuels includes measuring their gamma and neutron emissions typically with high-purity Germanium and He-3 detectors. In the past few years, however, efforts to develop efficient and low-cost, fast and thermal, neutron detectors have guided the research to the development of new scintillation detectors. These scintillators offer good efficiency, fast-timing properties, and good pulse shape discrimination capabilities for dual gamma and neutron detection. Within the Laboratory for Reactor Physics and Thermal-Hydraulics (LRT), a preliminary analysis was performed through Monte Carlo simulations to design a measurement unit at the HOTLAB based on new scintillators for the detection of fast neutrons emitted by spent fuel. This semester work of Marianna Papadionysiou was presented at the ANS Student conference in April and received two awards for "Best Detection and Measurement" and "Best Overall Research".

For the first time, researchers have produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Paul Scherrer Institute, in collaboration with their research partners, published the findings in the journal Nature Communications.

Among superconducting materials, CeCoIn₅ stands out as a rare case where superconductivity gives rise to magnetic order. An international team led by PSI physicist Michel Kenzelmann now reports that when small amounts of impurities are implanted into CeCoIn₅, then two distinct magnetic phases appear — and these are surprisingly similar to one another.

The magnetic order induced by the pressure was studied in FeSe by means of muon spin rotation (μSR) technique.

The electron beam energy of SwissFEL was recently increased to above 900 MeV by successfully bringing two new accelerating modules into operation. This allowed SwissFEL to produce laser radiation for the first time in the soft x-ray regime with a photon wavelength of 4.1 nm. During the next months, the electron beam energy will be progressively further increased with the goal of enabling first user experiments at a wavelength of around 0.5 nm towards the end of this year.

The electron beam energy of SwissFEL was recently increased to above 900 MeV by successfully bringing two new accelerating modules into operation. This allowed SwissFEL to produce laser radiation for the first time in the soft x-ray regime with a photon wavelength of 4.1 nm. During the next months, the electron beam energy will be progressively further increased with the goal of enabling first user experiments at a wavelength of around 0.5 nm towards the end of this year.

Interfaces are critical in quantum physics, and therefore we must explore the potential for designer hybrid materials that profit from promising combinatory effects. In particular, the fine-tuning of spin polarization at metallo–organic interfaces opens a realm of possibilities, from the direct applications in molecular spintronics and thin-film magnetism to biomedical imaging or quantum computing.

On May 11, 2017 the vacuum chambers of the first two offset mirrors have been closed eventually with the final gold- wire gasket and pumped down to ultra- high vacuum (goal: 1e-9 mbar). These mirrors are the key elements to switch the X-rays between the experimental stations. In pink beam mode they are the only optical elements for the X-rays on their way from the undulator down to the Alvra experiment.