Double charge ordering states and spin ordering state observed in a RFe2O4 system

Comprehensive Study of Oxygen Storage in YbFe2O4+x (x ≤ 0.5): Unprecedented Coexistence of FeOn Polyhedra in One Single Phase

The multiferroic LuFe^2.5+₂O₄ was recently proposed as a promising material for oxygen storage due to its easy reversible oxidation into LuFe³⁺₂O_4.5. We have investigated the similar scenario in YbFe₂O_4+x, leading to a slightly greater oxygen storage (OSC) capacity of 1434 μmol O/g. For the first time, the structural model of LnFe₂O_4.5 was fully understood by high-resolution microscopy images, and synchrotron and neutron diffraction experiments, as well as maximum entropy method. The oxygen uptake promotes a reconstructive shearing of the [YbO₂] sub-units controlled by the adaptive Ln/Fe oxygen coordination and the Fe^2/3+ redox. After oxidation, the rearrangement of the Fe coordination polyhedra is unique such that all available FeO_n units (n = 6, 5, 4 in octahedra, square pyramids, trigonal bipyramids, tetrahedra) were identified in modulated rows growing in plane. This complex pseudo-ordering gives rise to short-range antiferromagnetic correlation within an insulating state.

Coherent Nonlinear Optical Response Spatial Self-Phase Modulation in MoSe2 Nano-Sheets

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are drawing increasing interest due to their relatively high carrier mobilities, valley pseudospins, and gapped electronic structures, which all indicate interesting nonlinear optical properties of these 2D materials. However, such nonlinear optical properties are so far less investigated and their correlation with the electronic structure of the material is rarely probed. In this work, we have systematically investigated the spatial self-phase modulation (SSPM) of MoSe₂ flakes in a suspension form, which is a coherent third-order nonlinear optical effect. The nonlinear susceptibility χ⁽³⁾ and its wavelength-dependence are measured, yielding a value of 1.1 × 10⁻⁹ e.s.u. (SI: 1.53 × 10⁻¹⁷ m²/V²) at 532 nm laser excitation for effective one-layer MoSe₂.