Scientific Highlights
Square dance of the atoms: Shedding light on ultrafast phase transitions
The exploration of the interaction of structural and electronic degrees of freedom in strongly correlated electron systems on the femtosecond time scale is an emerging area of research. One goal of these studies is to advance our understanding of the underlying correlations, another to find ways to control the exciting properties of these materials on an ultrafast time scale. So far a general model is lacking that provides a quantitiative description of the correlations between the structural and electronic degrees of freedom.
Negative Oxygen Isotope Effect on the Static Spin Stripe Order in Superconducting La2−xBaxCuO4(x=1/8) Observed by Muon-Spin Rot
Large negative oxygen-isotope (16O and 18O) effects (OIEs) on the static spin-stripe-ordering temperature Tso and the magnetic volume fraction Vm were observed in La2−xBaxCuO4(x=1/8) by means of muon-spin-rotation experiments. The corresponding OIE exponents were found to be αTso=-0.57(6) and αVm=-0.71(9), which are sign reversed to αTC=0.46(6) measured for the superconducting transition temperature Tc. This indicates that the electron-lattice interaction is involved in the stripe formation and plays an important role in the competition between bulk superconductivity and static stripe order in the cuprates.
Direct observation of the spin texture in SmB6 as evidence of the topological Kondo insulator
Topological Kondo insulators have been proposed as a new class of topological insulators in which non-trivial surface states reside in the bulk Kondo band gap at low temperature due to strong spin–orbit coupling. In contrast to other three-dimensional topological insulators, a topological Kondo insulator is truly bulk insulating. Furthermore, strong electron correlations are present in the system, which may interact with the novel topological phase. By applying spin- and angle-resolved photoemission spectroscopy, here we show that the surface states of SmB6 are spin polarized. The spin is locked to the crystal momentum, fulfilling time reversal and crystal symmetries.
Small-angle neutron scattering study of the mixed state of Yb3Rh4Sn13
Using the small angle neutron scattering (SANS) technique we investigated the vortex lattice (VL) in the mixed state of the stannide superconductor Yb3Rh4Sn13. We find a single domain VL of slightly distorted hexagonal geometry for field strengths between 350 and 18 500 G and temperatures between T=0.05 and 6.5 K. We observe a clear in-plane rotation of the VL for different magnetic field directions relative to the crystallographic axes.
Spin-Wave Spectrum of the Quantum Ferromagnet on the Pyrochlore Lattice Lu2V2O7
Neutron inelastic scattering has been used to probe the spin dynamics of the quantum (S=1/2) ferromagnet on the pyrochlore lattice Lu2V2O7. Well-defined spin waves are observed at all energies and wave vectors, allowing us to determine the parameters of the Hamiltonian of the system.
Polychlorinated biphenyls in glaciers
We present a highly time-resolved historical record of polychlorinated biphenyls (PCBs) from an Alpine ice core (Fiescherhorn glacier, Switzerland). Introduced in the 1940s, PCBs were widely used industrial chemicals. Because of their persistence they are still found in the environment, long after their production phase-out. The Fiescherhorn ice core record covers the entire time period of industrial use of PCBs, that is, 1940?2002. The total concentration of six PCBs varies from 0.5 to 5 ng/L and reveals a temporal trend, with an 8-fold increase from the early 1940s to the peak value in the 1970s.
Coherent structural dynamics of a prototypical Charge-Density-Wave-to-Metal transition
In so called charge-density-wave compounds, the peculiar shape of the Fermi surface as well as electron-phonon coupling lead to a low-temperature broken symmetry ground state. This state is characterized by a modulation of the charge density (hence the name) and, via electron-phonon coupling, a distortion of the equilibrium lattice positions.
Origin of Anomalous Slip in Tungsten
Low-temperature deformation of body-centered cubic metals shows a significant amount of plastic slip on planes with low shear stresses, a phenomenon called anomalous slip. Despite progress in atomistic modeling of the consequences of complex stress states on dislocation mobility, the phenomenon of anomalous slip remained elusive. Using in situ Laue microdiffraction and discrete dislocation dynamics in micrometer sized tungsten single crystals, we demonstrate the occurrence of significant anomalous slip. It occurs as a consequence of cross kinks, topological configurations generated by prior dislocation interactions.
Identification of transitions between liquid water and ice with dual spectrum neutron imaging
The ability to start up at sub-zero Celsius temperatures is a prerequisite for the use of fuel cells in automotive applications, but specific measures need to be taken to prevent the product water to freeze and block the gas supply pathways. In this context, a method for imaging the distribution of liquid water and ice from neutron imaging experiments was developed.
First beam from the SwissFEL electron gun
The new 3 GHz photocathode gun will provide the electron bunches for SwissFEL and has recently been installed in the SwissFEL injector test facility. There, it replaced the CTF2-gun 5, borrowed from CERN. The new gun is capable now of operation with 100Hz repetition frequency and a higher field on cathode and improved field symmetry. After RF conditioning of about 4 days, the gun reached the nominal acceleration gradient of 100 MV/m at an input power of about 17 MW and pulse-width of 1 microsecond.