Scientific Highlights
Multi-q Mesoscale Magnetism in CeAuSb2
We report the discovery of a field driven transition from a single-q to multi-q spin density wave (SDW) in the tetragonal heavy fermion compound CeAuSb2. Polarized along c, the sinusoidal SDW amplitude is 1.8(2)μB/Ce for T<N=6.25(10)K with a wave vector q1=(η,η,1/2) [η=0.136(2)]. For H || c, harmonics appearing at 2q1 evidence a striped magnetic texture below μ0H1=2.78(1) T.
Are supersaturated calcium carbonate solutions classical or non-classical ?
Classical theory predicts that supersaturated carbonate solutions consist mostly of ions and ion pairs, with a small number of larger clusters present in the solution. The population of the different sized clusters in a solution is solely defined by the cluster’s size dependent Free Energy. If clusters are large enough they serve as nucleation germs for a new solid phase. The nucleation occurs once the surface free energy barrier posed by the new solid-liquid interface is overcome by the free energy win from bulk phase growth.
Giant multiphoton absorption points towards new methods for THz quantum control
In findings recently published in Nature Photonics, a team including researchers from the UK, the Netherlands and Photon Sciences division head Gabriel Aeppli have investigated multi-photon THz absorption in Si:P. Their studies, using the THz free-electron laser FELIX, discovered a two photon absorption cross-section ten orders of magnitude higher than that of a natural hydrogen atom and may enable new methods in quantum control. In addition to the original publication their findings are also discussed in a 'News and Views' article.
Quasistatic antiferromagnetism in the quantum wells of SmTiO3/SrTiO3 heterostructures
High carrier density quantum wells embedded within a Mott insulating matrix present a rich arena for exploring unconventional electronic phase behavior ranging from non-Fermi-liquid transport and signatures of quantum criticality to pseudogap formation. Probing the proposed connection between unconventional magnetotransport and incipient electronic order within these quantum wells has however remained an enduring challenge due to the ultra-thin layer thicknesses required.
Crystal-to-Crystal Transition of Ultrasoft Colloids under Shear
Ultrasoft colloids typically do not spontaneously crystallize, but rather vitrify, at high concentrations. Combining in situ rheo–small-angle-neutron-scattering experiments and numerical simulations we show that shear facilitates crystallization of colloidal star polymers in the vicinity of their glass transition. With increasing shear rate well beyond rheological yielding, a transition is found from an initial bcc-dominated structure to an fcc-dominated one.
Identification of hole trapping sites in ZnO nanomaterials
Members of the Alvra group led an investigation into the fate of charge carrier dynamics in metal oxide semiconductor nanomaterials. The experiments were performed at the Advanced Photon Source (Argonne, IL, USA) and used a PSI-designed von Hamos geometry X-ray emission spectrometer that was constructed for the experiment to perform resonant XES measurements on a solution of 32 nm diameter ZnO nanoparticles photo-excited with 3.2 eV (355 nm) short laser pulses. The measurement showed that the hole-trapping takes place within less than 100 ps and the trapping site in the ZnO crystal lattice is at oxygen vacancies in the lattice. The trapping of the hole results in a local structural distortion, where the four neighbouring Zn atoms move away from the vacancy. The measurement demonstrated the strength of the RXES technique's ability to probe both the electronic and geometric structure of materials and the results were recently published in Nature Communications.
Three Dimensional Polarimetric Neutron Tomography of Magnetic Fields
Through the use of Time-of-Flight Three Dimensional Polarimetric Neutron Tomography (ToF 3DPNT) we have for the first time successfully demonstrated a technique capable of measuring and reconstructing three dimensional magnetic field strengths and directions unobtrusively and non-destructively with the potential to probe the interior of bulk samples which is not amenable otherwise.
How is sulfur incorporated in biogenic carbonates and how is it affected by hydrothermal alteration?
Sulfate in biogenic carbonates is an important proxy for reconstructing the marine sulfur cycle. To investigate the exact location of carbonate associated sulfate (CAS) in biogenic carbonates and the effects of diagenetic alteration on sulfur in carbonates, shells of the marine bivalve Arctica islandica were artificially altered in modified seawater. Sulfur XANES analyses showed that CAS in A. islandica is indeed incorporated into the mineral part of the pristine shell, most likely as a hydrated or partly hydrated sulfate phase. The multi-analytical approach of XANES and µ-XRF analyses, sulfur isotope measurements, NanoSIMS analyses, and microstructural analysis on thin-sections of the shell samples further revealed that the different sulfur in a bivalve shell sensitively reacts to artificially induced hydrothermal alteration.
Photoinduced transitions in magnetoresistive manganites: A comprehensive view
Using the FEMTO slicing source at SLS, we have studied the structural response during the photoinduced transition in a charge-ordered Pr1-xCaxMnO3 thin films. By investigating the dynamics of both superlattice reflections and regular Bragg peaks, we disentangle the different structural contributions and analyze their relevant time-scales. Comparing these results with studies of the charge order and magnetic dynamics, a comprehensive picture of the phase transition linked to a single critical fluence fc is proposed.
Unravelling structure sensitivity in CO2 hydrogenation over nickel
Using a unique set of well-defined silica-supported Ni nanoclusters (1–7 nm) and advanced characterization methods it was proved how structure sensitivity influences the mechanism of catalytic CO2 reduction, the nature of which has been long debated.