Forschung zu Covid-19

Measurement of the absolute value of the applied pressure in high-pressure muon and neutron experiments is a complicated task. It often requires the presence of a calibration material inside the sample volume, and could also cause additional time to obtain the response of the calibrant. Here we describe the use of optical calibrants for precise determination of the pressure value inside the piston-cylinder clamp cells.

Our French collaborators and CNRS produced an excellent short movie about our common n2EDM experiment. The apparatus is currently being set up in

UCN Area South. The collaboration is on track for commissioning of the apparatus with neutrons towards the end of 2022.

We present a study of Cu-substitution effects in 4f-Ce intermetallic compound CeAu_1-xCu_xGe, with potentially unusual electronic states, in the whole concentration range (x = 0.0 – 1.0). The parent CeAuGe compound, crystallizing in a non-centrosymmetric hexagonal structure, is a ferromagnetic semimetal with Curie temperature 10 K. Cu-doping on Au-site of CeAuGe, CeAu_1-xCu_xGe, changes the crystal structure from the non-centrosymmetric (P6₃mc) to centrosymmetric (P6₃/mmc) space group at the concentration x ∼ 0.5, where the c-lattice constant has a maximum value. Magnetic susceptibility and electrical resistivity measurements reveal that all Cu-doped compounds undergo magnetic phase transition near 10 K, with the maximum transition temperature of 12 K for x = 0.5. The neutron powder diffraction experiments show the ferromagnetic ordering of Ce³⁺ magnetic moments with a value of about 1.2 μ_B at 1.8 K, oriented perpendicular to the hexagonal c-axis. By using symmetry analysis, we have found the solutions for the magnetic structure in the ferromagnetic Shubnikov space groups Cmc'2₁′ and P2₁′/m' for x < 0.5 and x ≥ 0.5, respectively. Electrical resistivity ρ(T) exhibits a metallic temperature behaviour in all compositions. The resistivity ρ(T) has a local minimum in the paramagnetic state due to Kondo effects at high doping x = 0.8 and 1.0. At the small Cu-doping level, x  = 0.2, the resistivity shows a broad feature at the ferromagnetic transition temperature and an additional transition-like peculiarity at 2.5 K in the ferromagnetic state.

Excitonic insulators are usually considered to form via the condensation of a soft charge mode of bound electron-hole pairs. This, however, presumes that the soft exciton is of spin-singlet character. Early theoretical considerations have also predicted a very distinct scenario, in which the condensation of magnetic excitons results in an antiferromagnetic excitonic insulator state. Here we report resonant inelastic x-ray scattering (RIXS) measurements of Sr₃Ir₂O₇.

Researchers from Italy, in collaboration with the Paul Scherrer Institut, successfully used the macromolecular crystallography beamline X06DA-PXIII at the Swiss Light Source to characterize promising perovkites materials used in solar cells and other photodetector devices.

A team of scientists from Paul Scherrer Institut and Oak Ridge National Laboratory review recent experimental studies of spin dynamics in the rare-earth perovskite materials. These compounds show unconventional magnetic excitations at low temperatures, including confined and deconfined spinons as well as multimagnon states, which were revealed by means of high-resolution neutron spectroscopy. These observations demonstrate that the rare-earth perovskite magnets can provide realizations of various aspects of quantum low-dimensional physics.

Cu diimine complexes present a noble metal free alternative to classical Ru, Re, Ir and Pt based photosensitizers in solution photochemistry, photoelectrochemical or dye-sensitized solar cells. Optimization of these dyes requires an understanding of factors governing the key photochemical properties: excited state lifetime and emission quantum yield. Using pump-probe XAS and DFT calculations we have explored the involvement of exciplex formation in the deactivation of the photoexcited state.