Latest News

Here you find current and previous news from the NUM division. For scientific highlights, please have a look here.

Guguchia_PRL

Using Uniaxial Stress to Probe the Relationship between Competing Superconducting States in a Cuprate with Spin-stripe Order

We report muon spin rotation and magnetic susceptibility experiments on in-plane stress effects on the static spin-stripe order and superconductivity in the cuprate system La2−xBaxCuO4 with x = 0.115. An extremely low uniaxial stress of ∼0.1 GPa induces a substantial decrease in the magnetic volume fraction and a dramatic rise in the onset of 3D superconductivity, from ∼10 to 32 K.

Coutinho PRL

Global Fit to Modified Neutrino Couplings and the Cabibbo-Angle Anomaly

Recently, discrepancies of up to 4σ between the different determinations of the Cabibbo angle were observed. In this context, we point out that this “Cabibbo-angle anomaly” can be explained by lepton flavor universality violating new physics in the neutrino sector. However, modified neutrino couplings to standard model gauge bosons also affect many other observables sensitive to lepton flavor universality violation, which have to be taken into account in order to assess the viability of this explanation.

Lehmann Nat Nanotech

Relation between microscopic interactions and macroscopic properties in ferroics

The driving force in materials to spontaneously form states with magnetic or electric order is of fundamental importance for basic research and device technology. The macroscopic properties and functionalities of these ferroics depend on the size, distribution and morphology of domains; that is, of regions across which such uniform order is maintained. Typically, extrinsic factors such as strain profiles, grain size or annealing procedures control the size and shape of the domains, whereas intrinsic parameters are often difficult to extract due to the complexity of a processed material. Here, we achieve this separation ...

 

mu3e

Mu3e magnet arrived at PSI

After almost three years of planning, design and construction, the 31-ton, 2.6 Tesla superconducting magnet for the Mu3e experiment arrived today at PSI. The magnet delivery is an important milestone in the Mu3e experiment at the Laboratory of Particle Physics LTP, which will search for New Physics in muon decays over the next years.

 

Rosa et al

Colossal magnetoresistance in a nonsymmorphic antiferromagnetic insulator

Here we investigate antiferromagnetic Eu5In2Sb6, a nonsymmorphic Zintl phase. Our electrical transport data show that Eu5In2Sb6 is remarkably insulating and exhibits an exceptionally large negative magnetoresistance, which is consistent with the presence of magnetic polarons. From ab initio calculations, the paramagnetic state of Eu5In2Sb6 is a topologically nontrivial semimetal within the generalized gradient approximation (GGA), whereas an insulating state with trivial topological indices is obtained using a modified Becke−Johnson potential.

 

Zhang et al PRL

Many-Body Resonance in a Correlated Topological Kagome Antiferromagnet

We use scanning tunneling microscopy to elucidate the atomically resolved electronic structure in the strongly correlated kagome Weyl antiferromagnet Mn3Sn. In stark contrast to its broad single-particle electronic structure, we observe a pronounced resonance with a Fano line shape at the Fermi level resembling the many-body Kondo resonance. We find that this resonance does not arise from the step edges or atomic impurities but the intrinsic kagome lattice.

 

Sessi et al

Handedness-dependent quasiparticle interference in the two enantiomers of the topological chiral semimetal PdGa

It has recently been proposed that combining chirality with topological band theory results in a totally new class of fermions. Understanding how these unconventional quasiparticles propagate and interact remains largely unexplored so far. Here, we use scanning tunneling microscopy to visualize the electronic properties of the prototypical chiral topological semimetal PdGa.

 

Soter

Anna Sótér appointed Tenure Track Assistant Professor at ETH Zurich

Anna Sótér, currently Lecturer and SNSF Ambizione Fellow at ETH Zurich, formerly member of the PSI Laboratory for Particle Physics and member of the PSI Fellow program, has been appointed Tenure Track Assistant Professor of Low Energy Particle Physics. Anna Sótér’s research is in the area of exotic atoms, where particle physics, atomic physics and quantum optics meet.

Krieger et al

Proximity-Induced Odd-Frequency Superconductivity in a Topological Insulator

At an interface between a topological insulator (TI) and a conventional superconductor (SC), superconductivity has been predicted to change dramatically and exhibit novel correlations. In particular, the induced superconductivity by an s-wave SC in a TI can develop an order parameter with a p-wave component. Here we present experimental evidence for an unexpected proximity-induced novel super- conducting state in a thin layer of the prototypical TI, Bi2Se3 proximity coupled to Nb.

Park et al

Momentum-Dependent Magnon Lifetime in the Metallic Noncollinear Triangular Antiferromagnet CrB2

Noncollinear magnetic order arises for various reasons in several magnetic systems and exhibits interesting spin dynamics. Despite its ubiquitous presence, little is known of how magnons, otherwise stable quasiparticles, decay in these systems, particularly in metallic magnets. Using inelastic neutron scattering, we examine the magnetic excitation spectra in a metallic noncollinear antiferromagnet CrB2, in which Cr atoms form a triangular lattice and display incommensurate magnetic order. Our data show intrinsic magnon damping ...

 

npj

Macroscopic manifestation of domain-wall magnetism and magnetoelectric effect in a Néel-type skyrmion host

We report a magnetic state in GaV4Se8 which emerges exclusively in samples with mesoscale polar domains and not in polar mono- domain crystals. It is manifested by a sharp anomaly in the magnetic susceptibility and the magnetic torque, distinct from other anomalies observed also in polar mono-domain samples upon transitions between the cycloidal, the Néel-type skyrmion lattice and the ferromagnetic states.

 

webinar 3

LENS Webinar on New Directions in Instrumentation

On June 25 the League of Advanced European Neutron Source LENS organized a second webinar on "New Directions in Instrumentation". Artur Glavic (LIN) gave a presentation on "Neutrons for Magnetic Nanostructures on Surfaces: Beyond the Specular Intensity Wars", which is still available online.

Mena PRL

Thermal Control of Spin Excitations in the Coupled Ising-Chain Material RbCoCl3

We have used neutron spectroscopy to investigate the spin dynamics of the quantum (S=1/2) antiferromagnetic Ising chains in RbCoCl3. The structure and magnetic interactions in this material conspire to produce two magnetic phase transitions at low temperatures, presenting an ideal opportunity for thermal control of the chain environment. The high-resolution spectra we measure ...

 

Birjukovs et al

Phase boundary dynamics of bubble flow in a thick liquid metal layer under an applied magnetic field

We investigate argon bubble flow in liquid gallium within a container large enough to avoid wall effects. Flow with and without applied horizontal magnetic field is studied. We demonstrate the successful capture and quantification of the effects of applied magnetic field using dynamic neutron radiography and the previously developed and validated robust image processing pipeline, supported by the in silico reproduction of our experiment.

 

Cho et al

Z3-vestigial nematic order due to superconducting fluctuations in the doped topological insulators NbxBi2Se3 and CuxBi2Se3

A state of matter with a multi-component order parameter can give rise to vestigial order. In the vestigial phase, the primary order is only partially melted, leaving a remaining symmetry breaking behind, an effect driven by strong classical or quantum fluctuations. Vestigial states due to primary spin and charge-density-wave order have been discussed in iron-based and cuprate materials. Here we present the observation of a partially melted superconductivity in which pairing fluctuations condense at a separate phase transition and form a nematic state with broken Z3, i.e., three-state Potts-model symmetry.

 

Zooming in on water splitting, teaser

Zooming in on water splitting

Perovskite oxynitride materials can act as effective photocatalysts for water splitting driven by visible light. A combined neutron and x-ray study now provides unique insight into the underlying processes at the solid–liquid interface and highlights how solar-to-hydrogen conversion can be improved.

CDonnelly_photo_

Young Scientist Award 2020

The Young Scientist Award 2020 of the European Magnetism Association (EMA) goes to Claire Donnelly for advances in the experimental characterization of spin textures and their dynamics in three dimensions with X-ray techniques.

Claire Donnelly, a former Ph.D. and postdoc at PSI in the Mesoscopic Systems Group, is currently a Leverhulme Early Career Research Fellow in the Cavendish Laboratory, University of Cambridge. She received her PhD in 2017 from the ETH Zurich for her work on hard X-ray tomography of three-dimensional magnetic structures based at the Paul Scherrer Institute. Following a postdoc at the ETH Zurich, she moved to the University of Cambridge and the Cavendish in January 2019, where she is focusing on the dynamics of three-dimensional magnetic nanostructures.

Her research focuses on three dimensional magnetic systems, which she studies using sophisticated synchorotron X-rays to determine the three-dimensional magnetic configurations, and their dynamic behaviour, at the nanoscale.

Shang et al

Simultaneous Nodal Superconductivity and Time-Reversal Symmetry Breaking in the Noncentrosymmetric Superconductor CaPtAs

By employing a series of experimental techniques, we provide clear evidence that CaPtAs represents a rare example of a noncentrosymmetric superconductor which simultaneously exhibits nodes in the superconducting gap and broken time-reversal symmetry (TRS) in its superconducting state (belowTc ≈ 1.5 K). Unlike in fully gapped superconductors, the magnetic penetration depth λ(T) does not saturate at low temperatures, but instead it shows a T2 dependence, characteristic of gap nodes.

Grinenko et al

Superconductivity with broken time-reversal symmetry inside a superconducting s-wave state

In general, magnetism and superconductivity are antagonistic to each other. However, there are several families of superconductors in which superconductivity coexists with magnetism, and a few examples are known where the superconductivity itself induces spontaneous magnetism. The best known of these compounds are Sr2RuO4 and some non-centrosymmetric superconductors. Here, we report the finding of ...

Pionic helium teaser

Laser focus on mesons

The first demonstration of laser spectroscopy of a meson, achieved at PSI's πE5 beamline, opens up new avenues for precision studies of ‘exotic atoms’.

Han purple

Understanding Quantum Critical Magnetism in Han Purple

The ancient purple pigment used to paint the terracotta warriors, BaCuSi2O6, is also a quantum magnetic material which consists of stacked Cu2+ bilayers hosting spin dimers. Magnetometry and NMR experiments have revealed puzzling critical phenomena at the quantum phase transition (QPT) caused by an applied magnetic field, which suggest that the universal behaviour of the system is not three- but only two-dimensional. By performing high-resolution neutron spectroscopy measurements .....

 

CMS 2020

Measurement of properties of Bs0 → μ+μ− decays and search for B0 → μ+μ− with the CMS experiment

Results are reported for the B0s → μ+μ branching fraction and effective lifetime and from a search for the decay B0 → μ+μ−. The analysis uses a data sample of proton-proton collisions accumulated by the CMS experiment in 2011, 2012, and 2016, with center-of-mass energies (integrated luminosities) of 7TeV (5fb−1), 8TeV (20fb−1),and 13TeV (36fb−1).

Teaser neutron stroboscopy

Batteries under the neutron stroboscope

The first application of stroboscopic neutron diffraction to studying lithium-ion batteries during operation establishes a new approach to unravelling the complex processes playing out in energy-storage materials.

Lawley et al

Examining the surface evolution of LaTiOxNy an oxynitride solar water splitting photocatalyst

LaTiOxNy oxynitride thin films are employed to study the surface modifications at the solid- liquid interface that occur during photoelectrocatalytic water splitting. Neutron reflectometry and grazing incidence x-ray absorption spectroscopy were utilised to distinguish between the surface and bulk signals, with a surface sensitivity of 3 nm.

Balsini PNAS

Electron–phonon-driven three-dimensional metallicity in an insulating cuprate

Elucidating the role of different degrees of freedom in a phase transition is crucial in the comprehension of complex materi- als. A phase transformation that attracts significant interest is the insulator-to-metal transition of Mott insulators, in which the electrons are thought to play the dominant role. Here, we use ultrafast laser spectroscopy and theoretical calculations ....

Octupole teaser

Spin ice expands to higher orders

With experimental work demonstrating that the correlated ground state of the pyrochlore system Ce2Sn2O7 is a quantum liquid of magnetic octupoles, an international team led by PSI researcher Romain Sibille establishes a fundamentally new state of matter: higher-rank multipole ice.

Octupole teaser

A quantum liquid of magnetic octupoles on the pyrochlore lattice

With experimental work demonstrating that the correlated ground state of the pyrochlore system Ce2Sn2O7 is a quantum liquid of magnetic octupoles, an international team led by PSI researcher Romain Sibille establishes a fundamentally new state of matter: higher-rank multipole ice.