Scientific Highlights
Coexistence of 3d-Ferromagnetism and Superconductivity in [(Li1-Fex)OH](Fe1-yLiy)Se
Superconducting [(Li1-xFex)OH](Fe1-yLiy)Se (x≈0.2, y≈0.08) was synthesized by hydrothermal methods and characterized by single-crystal and powder X-ray diffrac- tion. The structure contains alternating layers of anti-PbO type (Fe1-yLiy)Se and (Li1-xFex)OH. Electrical resistivity and magnetic susceptibility measurements reveal superconductivity at 43K.
Fractional excitations in the square-lattice quantum antiferromagnet
Quantum magnets have occupied the fertile ground between many-body theory and low-temperature experiments on real materials since the early days of quantum mechanics. However, our understanding of even deceptively simple systems of interacting spin-1/2 particles is far from complete. The quantum square-lattice Heisenberg antiferromagnet, for example, exhibits a striking anomaly of hitherto unknown origin in its magnetic excitation spectrum.
A measurement of the neutron to 199Hg magnetic moment ratio
The neutron gyromagnetic ratio has been measured relative to that of the 199Hg atom with an uncertainty of 0.8 ppm. We employed an apparatus where ultracold neutrons and mercury atoms are stored in the same volume and report the result γn/γHg = 3.8424574(30).
Short-Range Correlations in the Magnetic Ground State of Na4Ir3O8
The magnetic ground state of the Jeff = 1/2 hyperkagome lattice in Na4Ir3O8 is explored via combined bulk magnetization, muon spin relaxation, and neutron scattering measurements. A short-range, frozen state comprised of quasistatic moments develops below a characteristic temperature of TF = 6K, revealing an inhomogeneous distribution of spins occupying the entirety of the sample volume. Quasistatic, short- range spin correlations persist until at least 20 mK and differ substantially from the nominally dynamic response of a quantum spin liquid. Our data demonstrate that an inhomogeneous magnetic ground state arises in Na4Ir3O8 driven either by disorder inherent to the creation of the hyperkagome lattice itself or stabilized via quantum fluctuations.
Measurement of the parameter ξ″ in polarized muon decay and implications on exotic couplings of the leptonic weak interaction
The muon decay parameter ξ″ has been determined in a measurement of the longitudinal polarization of positrons emitted from polarized and depolarized muons. The result, ξ″ = 0.981 ± 0.045stat ± 0.003syst, is consistent with the Standard Model prediction of unity, and provides an order of magnitude improvement in the relative precision of this parameter. This value sets new constraints on exotic couplings beyond the dominant V-A description of the leptonic weak interaction.
Innovation Award on Synchrotron Radiation 2014 for high-resolution 3D hard X-ray microscopy
The 2014 Innovation Award on Synchrotron Radiation was bestowed to researchers Ana Diaz, Manuel Guizar-Sicairos, Mirko Holler, and Jörg Raabe from the Paul Scherrer Institut, Switzerland, for their contributions to method and instrumentation development, which have set new standards in high-resolution 3D hard X-ray microscopy.
k=0 Magnetic Structure and Absence of Ferroelectricity in SmFeO3
SmFeO3 has attracted considerable attention very recently due to its reported multiferroic properties above room temperature. We have performed powder and single crystal neutron diffraction as well as complementary polarization dependent soft X-ray absorption spectroscopy measurements on floating-zone grown SmFeO3 single crystals in order to determine its magnetic structure. We found a k=0 G-type collinear antiferromagnetic structure that is not compatible with inverse Dzyaloshinskii-Moriya interaction driven ferroelectricity. While the structural data reveal a clear sign for magneto-elastic coupling at the Néel-temperature of ∼675 K, the dielectric measurements remain silent as far as ferroelectricity is concerned.
A high-pressure hydrogen time projection chamber for the MuCap experiment
The MuCap experiment at the Paul Scherrer Institute performed a high-precision measurement of the rate of the basic electroweak process of nuclear muon capture by the proton, μ- + p → n + νμ. The experimental approach was based on the use of a time projection chamber (TPC) that operated in pure hydrogen gas at a pressure of 10 bar and functioned as an active muon stopping target. The TPC detected the tracks of individual muon arrivals in three dimensions, while the trajectories of outgoing decay (Michel) electrons were measured by two surrounding wire chambers and a plastic scintillation hodoscope.
Molecular Scale Dynamics of Large Ring Polymers
We present neutron scattering data on the structure and dynamics of melts from polyethylene oxide rings with molecular weights up to ten times the entanglement mass of the linear counterpart. The data reveal a very compact conformation displaying a structure approaching a mass fractal, as hypothesized by recent simulation work. The dynamics is characterized by a fast Rouse relaxation of subunits (loops) and a slower dynamics displaying a lattice animal-like loop displacement.
Multiferroic Properties of o−LuMnO3 Controlled by b-Axis Strain
Strain is a leading candidate for controlling magnetoelectric coupling in multiferroics. Here, we use x-ray diffraction to study the coupling between magnetic order and structural distortion in epitaxial films of the orthorhombic (o-) perovskite LuMnO3. An antiferromagnetic spin canting in the E-type magnetic structure is shown to be related to the ferroelectrically induced structural distortion and to a change in the magnetic propagation vector.