Transition énergétique

Within this synergetic collaboration, PSI scientists have investigated the correlation between magnetic and electronic ordering in NdNiO3 by tuning its properties through proximity to a ferromagnetic manganite layer. The main outcome is that the stray magnetic field from the manganite layer causes a novel ferromagnetic-metallic (FM-M) phase in NNO. This work demonstrates the utilization of heterostructure engineering for creating novel quantum phases.

Perovskite oxynitride semiconductors have attracted huge interest recently as promising photoelectrode materials for photoelectrochemical (PEC) water splitting. Oxynitride thin films grown by physical vapor deposition are ideal model systems to study the fundamental physical and chemical properties of the surface of these materials, including their evolution. Using a combination of high-sensitivity low-energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS), the surface evolution of LaTiO_xN_y (LTON) and CaNbO_xN_y (CNON) thin films before and after the PEC characterizations is monitored. This work provides therefore insight into the surface characteristics and evolution of LTON and CNON oxynitride thin films as photoelectrodes for PEC applications.

Researchers from University of Zurich describe the experimental observation of a new orthorhombic structural phase in the superconducting iron-pnictide compound Pr₄Fe₂As₂Te_0.88O₄. In contrast to nematicity found in underdoped iron pnictides this phase transition is not electronically driven. 

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Employing X-ray magnetic circular dichroism (XMCD), angle-resolved photoemission spectroscopy (ARPES), and momentum-resolved density fluctuation (MRDF) theory, the magnetic and electronic properties of ultrathin NdNiO₃ (NNO) film in proximity to ferromagnetic (FM) La_0.67Sr_0.33MnO₃ (LSMO) layer are investigated. The experimental data shows the direct magnetic coupling between the nickelate film and the manganite layer which causes an unusual ferromagnetic (FM) phase in NNO. Moreover, it is shown the metal–insulator transition in the NNO layer, identified by an abrupt suppression of ARPES spectral weight near the Fermi level (E_F), is absent. This observation suggests that the insulating AFM ground state is quenched in proximity to the FM layer. Combining the experimental data (XMCD and AREPS) with the momentum-resolved density fluctuation calculation (MRDF) reveals a direct link between the MIT and the magnetic orders in NNO systems. This work demonstrates that the proximity layer order can be broadly used to modify physical properties and enrich the phase diagram of RENiO₃ (RE = rare-earth element).

The crystal structure and magnetic correlations in triangular antiferromagnet FeGa2S4 are studied by x-ray diffraction, magnetic susceptibility, neutron diffraction, and neutron inelastic scattering. We report significant mixing at the cation sites and disentangle magnetic properties dominated by major and minor magnetic sites.

A novel and noninvasive method for high-energy two-color x-ray FEL emission was demonstrated at SwissFEL. In the experiment, a laser emittance spoiler pulse is overlapped with the primary photocathode laser pulse to locally spoil the beam emittance and inhibit the FEL emission from the central part of the beam, ultimately resulting in X-ray emission at two wavelengths. High spectral stability and the possibility to independently control the duration and intensity ratio between the two-color X-ray pulses is demonstrated. The laser emittance spoiler also enables shot-to-shot selection between one and two-color FEL emission and further, as it does not contribute to beam losses, it is compatible with high repetition-rate FELs.

This article has been selected as the winner of the first Ernest Courant Outstanding Paper Recognition, a honor sponsored by the journal Physical Review Accelerators and Beams (PRAB) and the APS Division of Physics of Beams (DPB).  This honor recognizes the most outstanding paper published in PRAB annually.

GeTe that exhibits a strong anharmonicity and a ferroelectric phase transition between the rhombohedral and cubic structures has emerged as one of the leading thermoelectric materials. Herein, combining molecular dynamics simulations and inelastic neutron scattering measurements, the lattice dynamics in GeTe have been investigated to reveal the soft-mode mechanisms across the phase transition.

The introduction of tin into ceria strongly influences its reducibility. In turn, the reaction mechanism towards the oxidation of carbon monoxide changes: the oxidation rate increases, the apparent activation energy decreases and the reaction order in oxygen increases.

Cryo-full-field XANES computed tomography was used to visualize the presence and distribution of a second coordination polymer of reduced copper coordination within defect-engineered HKUST-1 MOF crystals. Observations encourage a revisitation of the structure-property relationships of defect-engineered MOFs.