Scientific Highlights and News
When magnetism meets topology, colorful novel states can emerge in condensed matter. It is widely believed that parity-time symmetry plays an essential role for the formation of Dirac states in Dirac semimetals. So far, all of the experimentally identified topological nontrivial Dirac semimetals possess both parity and time reversal symmetry. Since the magnetism will break time-reversal symmetry, only in special cases the Dirac states can be protected in a magnetic system. Thus, the realization of magnetic topological Dirac materials remains a major issue in the research of topological physics. In this work, the authors ascertained that the ground state of EuCd2As2 is a good candidate for magnetic topological Dirac semimetal when the spins point in the out-of-plane direction in the A-type antiferromagnetic phase. The Dirac state is protected by the combination of parity-time symmetry with additional translation operation. Moreover, when the spins deviate from out-of-plane direction, the bulk Dirac cone will open a gap, and the system develops into a novel state containing axion insulator, antiferromagnetic topological crystalline insulator, and higher order topological insulator.
3D imaging using synchrotron radiation is a widely used tool that allows access to the inner structure of complex objects. An international and interdisciplinary consortium of scientists from the Swiss Light Source (PolLux and cSAXs), the Friedrich-Alexander-Universität Erlangen-Nürnberg, and the University of Cambridge developed the new 3D imaging technique of Soft X-ray Laminography (SoXL). SoXL allows for the investigation of thin and extended samples while taking advantage of the characteristic absorption contrast mechanisms in the soft X-ray range, providing 3D information with nm spatial resolution.
X-rays and neutrons has been used to investigate the correlation between structural and magnetic chirality in magnetic fields and its impact on the polarization in multiferroic langasites. A long wavelength modulation of the magnetic structure has been found, and it is shown that the chirality of the crystals structure connects to chirality of the magnetic structure that leads to an additional electric polarization in this field induced phase, which, depending on the christal chirality, can either increase the electric polarization or lead to a reversal of it for increasing magnetic fields. The theoretical description based on allowed Lifshitz invariants intriguingly contain all the essential ingredients for the realization of topologically stable antiferromagnetic skyrmions.
Ultra-fast operando X-ray diffraction experiments reveal the temporal evolution of low and high temperature phases and the formation of residual stresses during laser 3D printing of a Ti-6Al-4V alloy. The profound influence of the length of the laser-scanning vector on the evolving microstructure is revealed and elucidated.
Interrupted standard tensile tests with in situ x-ray diffraction and quasi-in situ electron backscatter diffraction reveal the origin behind the work hardening plateau and springback.
Via femtosecond x-ray diffraction, we observe an ultrafast increase of the octahedral rotation angle in the perovskite EuTiO3 after ultrafast laser excitation. This is opposite to what is expected from an increase in temperature. We ascribe this increase to an effective change of ionic sizes that transforms directly into a change of the Goldschmidt tolerance factor. Rotating oxygen octahedra at will opens up the possibility to control electronic and magnetic properties of perovskites on ultrafast timescales.
The newest large research facility at the Paul Scherrer Institute, SwissFEL, has been completed. In January 2019 it began regular operation. Henrik Lemke, head of the SwissFEL Bernina research group, gives an interim report.
A particular variety of particles, the so-called Weyl fermions, had previously only been detected in certain non-magnetic materials. But now researchers at PSI have experimentally proved their existence for the first time in a specific paramagnetic material.
PSI School for Master Degree Students - Introducing Photons, Neutrons and Muons for Condensed Matter Physics and Materials Science
From 17 – 21 June 2019 the Neutron and Muon Division (NUM) and the Photon Science Division (PSD) of PSI hosted 18 Master Degree students of physics, chemistry, materials and interdisciplinary science, as well as nuclear engineering to provide an introduction to the characterization of materials with large scale facilities like SINQ, SμS, SLS and SwissFEL. The course taught a basic understanding of how photons, neutrons and muons interact with matter, and how this knowledge can be used to solve specific problems in materials research.
Details of the program can be found at http://indico.psi.ch/event/PSImasterschool