Scientific Highlights

In high-temperature cuprate superconductors, stripe order refers broadly to a coupled spin and charge modulation with a commensuration of eight and four lattice units, respectively. How this stripe order evolves across optimal doping remains a controversial question. Here we present a systematic resonant inelastic x-ray scattering study of weak charge correlations in La_2−xSr_xCuO₄ and La_1.8−xEu_0.2Sr_xCuO₄. Ultra high energy resolution experiments demonstrate the importance of the separation of inelastic and elastic scattering processes. Long-range temperature-dependent stripe order is only found below optimal doping. At higher doping, short-range temperature-independent correlations are present up to the highest doping measured. This transformation is distinct from and preempts the pseudogap critical doping. We argue that the doping and temperature-independent short-range correlations originate from unresolved electron–phonon coupling that broadly peaks at the stripe ordering vector. In La_2−xSr_xCuO₄, long-range static stripe order vanishes around optimal doping and we discuss both quantum critical and crossover scenarios.

In high-temperature cuprate superconductors, stripe order refers broadly to a coupled spin and charge modulation with a commensuration of eight and four lattice units, respectively. How this stripe order evolves across optimal doping remains a controversial question. Here we present a systematic resonant inelastic x-ray scattering study of weak charge correlations in La_2−xSr_xCuO₄ and La_1.8−xEu_0.2Sr_xCuO₄. Ultra high energy resolution experiments demonstrate the importance of the separation of inelastic and elastic scattering processes.

The ability to start-up in extreme environmental conditions, including sub-freezing temperatures, is essential to the deployment of the fuel cell technology. Water produced in fuel cells at these temperatures can be in the super-cooled state, and freezing can lead to a rapid shutdown, as water cannot be removed anymore as a liquid. By segmenting a fuel cell, it is possible to prevent the propagation of freezing, which enables the cell operation even after the first freezing event occurred.

From new neutron powder diffraction experiments on the chiral cubic (P213) magnet manganese germanide (MnGe), we analyze all of the possible crystal symmetry-allowed magnetic superstructures that are determined successfully from the data. The incommensurate propagation vectors k of the magnetic structure are found to be aligned with the [100] cubic axes, and correspond to a magnetic periodicity of about 30 Å at 1.8 K. Several maximal crystallographic symmetry magnetic structures are found to fit the data equally well and are presented. These include topologically nontrivial magnetic hedgehog and “skyrmion” structures in multi-k cubic or orthorhombic 3+3 and orthorhombic 3+2 dimensional magnetic superspace groups respectively, with either potentially responsible for topological Hall effect. The presence of orthorhombic distortions in the space group P212121 caused by the transition to the magnetically ordered state does not favor the cubic magnetic hedgehog structure, and leave both orthorhombic hedgehog and skyrmion models as equal candidates for the magnetic structures. We also report on a combined mechanochemical and solid-state chemical route to synthesize MnGe at ambient pressures and moderate temperatures, and compare with samples obtained by the traditional high pressure synthesis.

We present magnetization and neutron powder diffraction studies in the temperature range 2K to 300K for oxygen stoichiometric R_1/3Sr_2/3FeO (R = Pr and Nd). From full symmetry analysis, we proposed two magnetic models by a combined application of irreducible representations and magnetic space groups. Both models fit equally well the neutron powder diffraction data.