Structural transition and superconductivity in hydrothermally synthesized FeX (X = S, Se)

Tetragonal beta-FeSe obtained by hydrothermal reaction is not superconducting and transforms to a triclinic structure at 60 K unlike superconducting FeSe from solid state synthesis, which becomes orthorhombic at 90 K. In contrast, tetragonal iron sulphide FeS from hydrothermal synthesis is superconducting at 4.8 K but undergoes no structural transition. Our results suggest that the absence of superconductivity in hydrothermally synthesized FeSe may be associated to the low-temperature structure with zigzag chains of iron atoms, which is different from the known orthorhombic Cmme structure of superconducting FeSe.Comment: 4 pages, 7 figure

Bright circularly polarized photoluminescence in chiral layered hybrid lead-halide perovskites.

Hybrid perovskite semiconductor materials are predicted to lock chirality into place and encode asymmetry into their electronic states, while softness of their crystal lattice accommodates lattice strain to maintain high crystal quality with low defect densities, necessary for high luminescence yields. We report photoluminescence quantum efficiencies as high as 39% and degrees of circularly polarized photoluminescence of up to 52%, at room temperature, in the chiral layered hybrid lead-halide perovskites (R/S/Rac)-3BrMBA2PbI4 [3BrMBA = 1-(3-bromphenyl)-ethylamine]. Using transient chiroptical spectroscopy, we explain the excellent photoluminescence yields from suppression of nonradiative loss channels and high rates of radiative recombination. We further find that photoexcitations show polarization lifetimes that exceed the time scales of radiative decays, which rationalize the high degrees of polarized luminescence. Our findings pave the way toward high-performance solution-processed photonic systems for chiroptical applications and chiral-spintronic logic at room temperature

Strong Induced Circular Dichroism in a Hybrid Lead‐Halide Semiconductor Using Chiral Amino Acids for Crystallite Surface Functionalization

Chirality is a desired property in functional semiconductors for optoelectronic, catalytic, and spintronic applications. Here, introducing enantiomerically-pure 3-aminobutyric acid (3-ABA) into thin films of the 1D semiconductor dimethylammonium lead iodide (DMAPbI$_3$) is found to result in strong circular dichroism (CD) in the optical absorption. X-ray diffraction and grazing incidence small angle X-ray scattering (GISAXS) are applied to gain molecular-scale insights into the chirality transfer mechanism, which is attributed to a chiral surface modification of DMAPbI$_3$ crystallites. This study demonstrates that the CD signal strength can be controlled by the amino-acid content relative to the crystallite surface area. The CD intensity is tuned by the composition of the precursor solution and the spin-coating time, thereby achieving anisotropy factors (g$_{abs}$) as high as 1.75 × 10$^{–2}$. Grazing incidence wide angle scattering reveals strong preferential ordering that can be suppressed via tailored synthesis conditions. Different contributions to the chiroptical properties are resolved by a detailed analysis of the CD signal utilizing an approach based on the Mueller matrix model. This report of a novel class of chiral hybrid semiconductors with precise control over their optical activity presents a promising approach for the design of circularly polarized light detectors and emitters

Halogen variations through the quenched margin of a MORB lava: evidence for direct assimilation of seawater during eruption

Halogens and noble gases within submarine basaltic glasses are critical tracers of interactions between the surface volatile reservoirs and the mantle. However, as the halogens and noble gases are concentrated within seawater, sediments, and the oceanic crust this makes the original volatile signature of submarine basaltic lavas susceptible to geochemical overprinting. This study combines halogen (Cl, Br, and I), noble gas, and K concentrations within a single submarine basaltic quenched margin to quantify the amount of seawater assimilation during eruption, and to further elucidate the mechanisms of overprinting. The outer sections of the glass rim are enriched in Cl compared to the interior of the margin, which maintains mantle-like Br/Cl, I/Cl, and K/Cl ratios. Low Br/Cl and K/Cl in the outer sections of the basaltic glass margin indicate that the Cl enrichment in the outer glass is derived from the assimilation of a saline brine component with up to 70% of the Cl within the glass being derived from brine assimilation. Atmospheric noble gas contamination is decoupled from halogen contamination with contaminated outer sections maintaining MORB-like 40Ar/36Ar, suggesting seawater-derived brine assimilation during eruption is not the dominant source of atmospheric noble gases in submarine basalts. Volatile heterogeneities in submarine basalts introduced during and after eruption, as we have shown in this study, have the potential to expand the range of mantle halogen compositions and only by better understanding these heterogeneities can the Br/Cl and I/Cl variance in mantle derived samples are determined accurately