For the SLS, the proposal cycle continues but we need to keep in mind that changing travel restrictions may severely impact the user program. Remote access and mail-in should be considered to ensure that experimental campaigns can take place. For SwissFEL no new call for proposals has been launched and in the next semester we will schedule postponed experiments and high-quality proposals from the existing reserve list or the previous call.
 

Since September 1, also the facilities driven by the High-Intensity Proton Accelerator HIPA such as SINQ, SμS and the facilities for particle physics are open for external users again. For all facilities dedicated safety concepts have been developed aiming at the best possible protection for our users and staff.

In topological materials, electrons can display behaviour that is fundamentally different from that in ‘conventional’ matter. The magnitude of many such ‘exotic’ effects is directly proportional to an entity known as the Chern number. Experiments at the ADRESS beamline of SLS and at the Diamond Light Source (UK) establish now for the first time that the theoretically predicted maximum Chern number can be reached in a real material. The researchers set this benchmark studying the topological semimetal palladium gallium, in which they observed Chern numbers of magnitude 4 - the maximum value allowed in any metallic crystal. Moreover, they found ways to control the sign of the Chern number, which might bring new opportunities for exploring, and exploiting, topological phenomena.

Magnetic skyrmions are topologically stable spin textures that have attracted substantial interest, both for their deep conceptual connections to various fields of science and for future technological uses. Traditionally associated with ferromagnetic spin alignment, these nanoscale structures have been predicted to emerge as well in materials with antiferromagnetic arrangements of neighbouring spins. Researchers now report the first experimental realization of such antiferromagnetic skyrmions. Combining neutron scattering and Monte Carlo simulation, they establish that the recently discovered triple-q phase in the spinel MnSc₂S₄ hosts a fractional antiferromagnetic skyrmion lattice that is stabilized by anisotropic couplings. The work provides fresh perspectives for harnessing skyrmions in spintronic devices, potentially with more flexible control than is possible with ferromagnetic skyrmions.

The interface between a topological insulator (TI) and a superconductor is an arena for intriguing physics. An unexpected new example of that is the finding that a conventional niobium superconductor proximity-coupled to the prototypical TI Bi₂Se₃ induces odd-frequency superconductivity. For odd-frequency states, the correlation function describing the electrons of a Cooper pair is odd in time. Remarkably, in odd-frequency superconductors the Meissner effect can be paramagnetic rather than diamagnetic, as characteristically seen in superconductors. The researchers observed such paramagnetic Meissner screening by low-energy muon spin rotation performed at SμS, where they found - for the first time in a TI - an enhancement of applied magnetic fields inside Bi₂Se₃, caused by the induced odd-frequency pairing in the bulk.

In biology, structure and function are closely interwoven. A case in point is oxygen transport in the lungs, which relies on ferrous heme proteins adopting dome-like shapes. Previous work has suggested, however, that no such doming takes place in their ferric counterparts, where the coordination centre is Fe(III) rather than Fe(II). A study combining femtosecond X-ray emission spectroscopy (XES) and X-ray absorption near-edge structure (XANES) now challenges that assumption. Experiments performed at SwissFEL and the European XFEL provide evidence that in the ferric form of the heme protein cytochrome c, a cascade among excited spin states of the iron ion occurs upon photoexcitation, causing in turn doming - and raising fresh questions about the structure-function relationship in these complexes.

CALIPSOplus, a European Horizon 2020 funded research and innovation program, provides access support for SMEs to light sources. The access is based on a specific review system for SMEs in parallel to the established academic access route but following the same principles. Proposal confidentiality is ensured during the whole process. If the proposal is accepted, the SME will have access to the requested light sources and the experiments will be financially supported through CALIPSOplus. The current call is open from September 1 to December 21, 2020. More information.

During July, the SINQ guide upgrade project was completed and SINQ started to produce again neutrons. Many of the neutron instruments were put back into operation at the beginning of August. Expected recommissioning work on the instruments was performed in August, together with first in-house and friendly-user experiments. The user program started in earnest on September 1. A few remaining instruments, such as AMOR, DMC and CAMEA, will return into operation later this year and next year. All of this was and is possible thanks to the unbroken enthusiasm of the engineering and science teams at PSI that delivered most of the milestones of the SINQ upgrade project almost on time despite a global pandemic!

Starting from September 1, external/foreign users have been allowed to perform experiments at the SµS. However, as Swiss and foreign travel restrictions apply only very few users actually visited PSI. To cope with this unusual situation, the PSI team conducted most of the experiments with the remote support from the users. For experiments that could not be performed in this way, the approved beamtime has been shifted to the next year. This will create a major backlog for the next allocation periods.

On Friday June 26 late in the evening, the intense soft X-ray pulses from the Athos undulator lines have entered the Maloja endstation for the first time. Already in the following days electron, ion, and photon spectra were measured from single x-ray pulses. The technical, engineering, and scientific staff across divisions worked tirelessly also during the COVID-19 times to reach this milestone. The endstation will now go through thorough commissioning and commence user operations in 2021.

The Mu3e superconducting solenoid can reach fields up to 2.3 T in its warm bore of 1 m diameter and 2.3 m length. It was manufactured in London, UK, despite difficult circumstances due to the pandemic situation. The system is of the dry type, without cryogenic fluids. The superconducting coil is brought down to the required low temperatures using four double-staged Gifford-McMahon cryocoolers.
Currently the acceptance tests are ongoing and the solenoid will be transferred to the πE5 area later this year. Over the next few years, Mu3e is performing a search for the ultra-rare decay µ→eee using a novel silicon tracker and scintillators in a field of 1 T. The sensitivity for the branching ratio will be will be improved by 2-3 orders of magnitude in πE5 and can reach the 10^-16 level at the envisaged high intensity muon beam (HIMB), four orders of magnitude lower than the best current limit set by SINDRUM (also at PSI).

Copyright © 2020, Paul Scherrer Institut PSI

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The PSI Facility Newsletter addresses the users of the PSI large facilities and appears quarterly in English. Any feedback is highly welcome! More information. 

Contact: PSI User Office, Phone: +41-56-310-4666, Email: useroffice@psi.ch