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PSI Facility News IV/2022
20 December 2022

Dear Colleagues

We are on the home straight not only towards the end of the year at PSI, but also, and more importantly, towards the long shutdown for the SLS 2.0 upgrade, which will begin in October 2023. Although the worldwide delivery-chain problems are also affecting the procurements for the SLS, many important milestones have been successfully achieved. 

Frithjof Nolting

It is a complex and highly challenging task and this final spurt is in fact more of a first part of a triathlon. The 15-month shutdown of the machine with the construction inside the tunnel is the second stage, and starting in 2025, getting the SLS back running and in full user operation will be the third and final part. What should also not be forgotten is that on top of the upgrade of the synchrotron, the beamlines will be upgraded as well. This sounds like a long journey, but we are ready for it. Many people from very different fields worked hard for the preparation. And the excellent user community laid the foundation for the scientific drive that is the motivation behind all of it.

A big thank you to all the expert groups working on the realization of the SLS 2.0 upgrade.

Frithjof Nolting, Philip Willmott and Hans Braun
On behalf of the SLS 2.0 project

Next proposal submission deadlines

CHRISP 09 January 2023
SwissFEL 15 March 2023
SINQ 15 May 2023
SµS 01 June 2023
SLS tbd (SLS upgrade)
X+N powder diffraction tbd (SLS upgrade)

An overview of all proposal submission deadlines of the PSI facilities can be found here.

Research highlights

Nanomaterial from the Middle Ages

SLS — A modern look at a medieval bilayer metal leaf: nanotomography of Zwischgold

To gild sculptures in the late Middle Ages, artists often applied ultra-thin gold foil supported by a silver base layer. Scientists at PSI have now succeeded in producing for the first time nanoscale 3D images of this material, known as Zwischgold. The samples were unusual even for the highly experienced PSI team: minute amounts of material taken from three modern and four medieval samples, including an altar and wooden statues originating from the fifteenth century. Preforming ptychographic X-ray computed tomography (PXCT) at SLS, the team looked at the leaf structure and chemical state of the material. The measurements underline how highly sophisticated the mediaeval production technique for Zwischgold was, but also revealed increasing porosity of the leaf materials and their corrosion products, as well as delamination of the leaves from their substrate — issues typically observed in the conservation of such artefacts.

Q. Wu et al., Nanoscale 14, 15165 (2022)
DOI: 10.1039/d2nr03367d

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Graphene’s magic in a magnet

SINQ — Thermal evolution of Dirac magnons in the honeycomb ferromagnet CrBr₃

Graphene owes most its hailed physical properties to its honeycomb lattice structure. PSI researchers have now investigated its magnetic equivalent, chromium tribromide. This honeycomb ferromagnet possesses a lattice geometry identical to that of graphene, and remains magnetic in the limit of a single atomic layer. Using advanced neutron scattering at SINQ — working with the triple-axis spectrometer EIGER — and at the Institut Laue-Langevin in Grenoble, the team probed the magnetic band structures of CrBr3 at unrivalled resolution. In doing so, they provide an update to data obtained half a century ago, enabling a definitive comparison with recent experimental claims of a significant gap at the Dirac point and with theoretical predictions for thermal magnon renormalization — thereby setting the experimental standard for temperature-induced modification of the spin dynamics in a honeycomb ferromagnet.

S.E. Nikitin et al., Physical Review Letters 129, 127201 (2022)
DOI: 10.1103/PhysRevLett.129.127201

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Quantum coherence between muon spins and quadrupolar nuclei

SμS — Entanglement between muon and I > ½ nuclear spins as a probe of charge environment

Quantum coherence between implanted muons and the nuclei of the solid have been observed by muon-spin spectroscopy since the 1980s, but exclusively for the spin-½ nuclei fluorine and hydrogen. These studies received recently renewed interest in the context of using the muon–nuclear entangled states as sensitive probes of the microscopic environment inside the material. Now an international team of scientists observed at SμS such coherent oscillations for the first time between muons and nuclei with a higher nuclear moment, namely in vanadium intermetallic compounds (I = 7/2). This extension of the concept is particularly interesting as spins with I > ½ possess a quadrupolar moment, making them extremely sensitive to local structural and electronic environments. This work therefore establishes muons as a versatile quantum sensor for structural and charge-related phenomena in solids, even in the absence of magnetic order.

P. Bonfà et al., Physical Review Letters 129, 097205 (2022)
DOI: 10.1103/PhysRevLett.129.097205

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Controlling weight swings

SwissFEL — Strong modulation of carrier effective mass in WTe₂ via coherent lattice manipulation

The layered transition-metal dichalcogenide WTe2 is characterized by distinctive transport and topological properties. These emergent electronic properties can in principle be manipulated by changes in the crystal structure. However, how precisely a given structural change alters the electronic properties is typically difficult to determine, as direct structural probes with high time resolution are required. A team of researchers working at the Bernina beamline of SwissFEL has now followed the structural dynamics in WTe2 after excitation with femtosecond laser pulses, with particular focus on coherent phonon modes. Their time-resolved X-ray diffraction results, supported by infrared reflectivity measurements, suggest that phonons might periodically modulate the effective mass of carriers in the electron and hole pockets by up to 20% — indicating a route to controlling the peculiar transport properties of WTe2 on short time scales.

D. Soranzio et al., npj 2D Materials and Applications 6, 71 (2022)
DOI: 10.1038/s41699-022-00347-z

Exchange across disciplines and communities

CHRISP — PSI2022 workshop on the physics of fundamental symmetries and interactions

190 participants gathered at PSI from 17 to 22 October 2022 for PSI2022, the 6th edition of the ‘Physics of fundamental Symmetries and Interactions’ workshop. A central goal of the meeting series is to foster scientific discussions on various topics, thereby deepening relations across disciplines and scientists. In 60 plenary talks and 80 posters, recent results and future plans for particle-physics experiments and theory were presented, with an emphasis on muons, pions, neutrons, antiprotons, and atoms. An extended discussion of muonic atoms was the focus of a satellite event preceding the workshop. Following tradition, the poster session was combined with a BBQ. The Tuesday session was held as a hybrid event, shared with the FIPs (Feebly-Interacting Particles) workshop, which took place during the same week at CERN. On Thursday during the workshop dinner with raclette and local wine and beer, the three poster prizes sponsored by NuPECC (Nuclear Physics European Collaboration Committee) and PSI were awarded.

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3rd PSI Summer Camp 2022

Close to 100 participants came together in the Lyceum Alpinum in Zuoz for the 3rd PSI Condensed Matter Summer Camp, which took place from 8 to 12 August 2022. The camp provides a forum for leading scientists to meet and discuss fundamental aspects and open questions of current scientific interest. The theme of this year’s camp was “Coherence and Entanglement in Quantum Systems”, and 27 speakers covered a wide range of topics. Moreover, the camp offered young physicists didactical introductions to advanced concepts in condensed-matter physics, and served as an opportunity to network and to get a wider perspective on the rich field of condensed-matter physics. Next year’s PSI Condensed Matter Summer Camp will take place from 6 to 11 August 2023 and will focus on 2D quantum materials.

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News from the user facilities

SLS: First magnet series for SLS 2.0 measured

The SLS upgrade (SLS 2.0) is one of the largest projects at PSI for the coming years. It will significantly increase the performance of the SLS, while maintaining the current 288-metre circumference of the electron storage ring. To meet these requirements, a considerably higher number of much narrower and more sophisticated magnets are needed to keep the electrons on their orbit. In total, 1152 new customised magnets will be installed. Between mid-April and the end of September 2022, members of the magnet section of the Accelerator Technology Department in the Large Research Facilities Division of PSI successfully measured the first complete series of one type of magnet — 112 quadrupole electromagnets in four designs, which were conceived and constructed at PSI and built by the company SigmaPhi.

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SINQ/SμS: Recent proposal deadlines

In mid-November and early December there have been the last two proposal submission deadlines in 2022 for SINQ and SμS, respectively. For SINQ again a very large number of new proposals was submitted, 325. Together with the proposals submitted in May, we received almost 630 new beamtime applications in 2022. In comparison to the pre-pandemic years, the number of SINQ proposals has almost doubled, which reflects both the decrease in available neutron facilities in Europe and a highly active scientific community and their undiminished demand for beamtime. In this round most of the beam days have been requested again for the small-angle-scattering facility SANS-I (239), followed by the new multiplexing spectrometer CAMEA (166).

The demand for muon beam time remains on a very high level as well. In the latest call we received 191 new proposals. Together with the proposals in response to the June call, the total  number for 2022 is 279 SμS proposals — the second-highest number ever. In December the GPS instrument received again most of the proposals (58), followed by DOLLY (35) and the new instrument FLAME (34), which was open for proposals for the first time. For both SINQ and SμS the review panels will meet by the end of January; the results of the proposal rounds may be expected in February 2023.

SwissFEL/SLS: A piece of PSI history sets off on a long journey

The insertion device that has been used in the former Femtoslicing Facility at PSI has recently been shipped to the Australian Synchrotron in Melbourne. The 11.5-tonne device was used intensively for research at PSI for more than ten years, until 2017, in particular for femtoslicing — the generation of ultrashort synchrotron radiation pulses by laser-induced energy modulation of electrons. However, with the commissioning of SwissFEL, the device has reached the end of its service life. Now it will be given a new task in Australia, where it will serve the purpose for which it was originally designed: generating synchrotron radiation.

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CHRISP: Automatic conditioning at the UCN source

The high-intensity ultracold neutron (UCN) source serves three beam ports for experiments in standard operation, delivering eight-second-long proton pulses every 300 s. UCN production occurs in solid deuterium at 5 K. Heat impact from the high-power beam pulses, over hours and days, leads to surface degradation of the deuterium, accompanied by a decrease in UCN intensity. In recent years, a thermal surface-conditioning method was developed to recuperate the intensity. Recently, the method has been automatized and modified to use the energy of the proton pulse itself. As a consequence, the average UCN intensity at the beam port is now up by more than 20%.

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