gg-factor engineering with InAsSb alloys toward zero band gap limit

Band gap is known as an effective parameter for tuning the Lande $g$-factor in semiconductors and can be manipulated in a wide range through the bowing effect in ternary alloys. In this work, using the recently developed virtual substrate technique, high-quality InAsSb alloys throughout the whole Sb composition range are fabricated and a large $g$-factor of $g\approx -90$ at the minimum band gap of $\sim 0.1$ eV, which is almost twice that in bulk InSb is found. Further analysis to the zero gap limit reveals a possible gigantic $g$-factor of $g\approx -200$ with a peculiar relativistic Zeeman effect that disperses as the square root of magnetic field. Such a $g$-factor enhancement toward the narrow gap limit cannot be quantitatively described by the conventional Roth formula, as the orbital interaction effect between the nearly triply degenerated bands becomes the dominant source for the Zeeman splitting. These results may provide new insights into realizing large $g$-factors and spin polarized states in semiconductors and topological materials

Magnetic proximity-induced energy gap of topological surface states

Topological crystalline insulator surface states can acquire an energy gap when time reversal symmetry is broken by interfacing with a magnetic insulator. Such hybrid topological-magnetic insulator structures can be used to generate novel anomalous Hall effects and to control the magnetic state of the insulator in a spintronic device. In this work, the energy gap of topological surface states in proximity with a magnetic insulator is measured using Landau level spectroscopy. The measurements are carried out on Pb1-xSnxSe/EuSe heterostructures grown by molecular beam epitaxy exhibiting record mobility and a low Fermi energy enabling this measurement. We find an energy gap that does not exceed 20meV and we show that is due to the combined effect of quantum confinement and magnetic proximity. The presence of magnetism at the interface is confirmed by magnetometry and neutron reflectivity. The recovered energy gap sets an upper limit for the Fermi level needed to observe the quantized anomalous Hall effect using magnetic proximity heterostructures

The Magnetoelastic Distortion of Multiferroic BiFeO3_3 in the Canted Antiferromagnetic State

Using THz spectroscopy, we show that the spin-wave spectrum of multiferroic BiFeO$_3$ in its high-field canted antiferromagnetic state is well described by a spin model that violates rhombohedral symmetry. We demonstrate that the monoclinic distortion of the canted antiferromagnetic state is induced by the single-ion magnetoelastic coupling between the lattice and the two nearly anti-parallel spins. The revised spin model for BiFeO$_3$ contains two new single-ion anisotropy terms that violate rhombohedral symmetry and depend on the direction of the magnetic field.Comment: 28 pages (main & supplementary), 2 figures (main article), 15 figures (supplementary material

Vive la radiorésistance!: converging research in radiobiology and biogerontology to enhance human radioresistance for deep space exploration and colonization.

While many efforts have been made to pave the way toward human space colonization, little consideration has been given to the methods of protecting spacefarers against harsh cosmic and local radioactive environments and the high costs associated with protection from the deleterious physiological effects of exposure to high-Linear energy transfer (high-LET) radiation. Herein, we lay the foundations of a roadmap toward enhancing human radioresistance for the purposes of deep space colonization and exploration. We outline future research directions toward the goal of enhancing human radioresistance, including upregulation of endogenous repair and radioprotective mechanisms, possible leeways into gene therapy in order to enhance radioresistance via the translation of exogenous and engineered DNA repair and radioprotective mechanisms, the substitution of organic molecules with fortified isoforms, and methods of slowing metabolic activity while preserving cognitive function. We conclude by presenting the known associations between radioresistance and longevity, and articulating the position that enhancing human radioresistance is likely to extend the healthspan of human spacefarers as well

Ultrafast structural changes direct the first molecular events of vision

視覚に関わるタンパク質の超高速分子動画 --薄暗いところで光を感じる仕組み--. 京都大学プレスリリース. 2023-03-23.Vision is initiated by the rhodopsin family of light-sensitive G protein-coupled receptors (GPCRs). A photon is absorbed by the 11-cis retinal chromophore of rhodopsin, which isomerizes within 200 femtoseconds to the all-trans conformation, thereby initiating the cellular signal transduction processes that ultimately lead to vision. However, the intramolecular mechanism by which the photoactivated retinal induces the activation events inside rhodopsin remains experimentally unclear. Here we use ultrafast time-resolved crystallography at room temperature to determine how an isomerized twisted all-trans retinal stores the photon energy that is required to initiate the protein conformational changes associated with the formation of the G protein-binding signalling state. The distorted retinal at a 1-ps time delay after photoactivation has pulled away from half of its numerous interactions with its binding pocket, and the excess of the photon energy is released through an anisotropic protein breathing motion in the direction of the extracellular space. Notably, the very early structural motions in the protein side chains of rhodopsin appear in regions that are involved in later stages of the conserved class A GPCR activation mechanism. Our study sheds light on the earliest stages of vision in vertebrates and points to fundamental aspects of the molecular mechanisms of agonist-mediated GPCR activation

Computing in High Energy and Nuclear Physics (CHEP) 2012

One of the most crucial requirement for online storage is the fast and efficient access to data. Although smart client side caching often compensates for discomforts like latencies and server disk congestion, spinning disks, with their limited ability to serve multi stream random access patterns, seem to be the cause of most of the observed inefficiencies. With the appearance of the different variants of solid state disks (SSD), this deficiency could be overcome, however, replacing the entire experiment data repositories by SSDs is not feasible in the foreseeable future. Moreover, spinning disks are still appropriate media for controlled streaming applications. Assuming a deployment of a mixture of media, like spinning disks, SSDs and tape, at a site, the authors argue for the introduction of a three tier media structure within a single storage system with automatic transitions, based on usage patterns, in contrast to interlinking and maintaining different mediatypes in different systems with external procedures taking care of proper data placement. The feasibility of the suggested approach is studied, using the analysis of access logs of the DESY WLCG Tier II storage elements, hosting the largest part of the data to be analyzed by the CMS and ATLAS Collaborations. Finally we will report on a prototype implementing of the three tier media structure into dCache, a storage technology widely used in WLCG

Mass mortality event of White Sea sponges as the result of high temperature in summer 2018

International audienc

Gas phase ZnO nanoclusters and structural, optical and lasing properties of corresponding nanostructured thin films

International audienceIn this communication we present a pulsed laser ablation (PLA) method of synthesis of high quality nanostructured thin films for optoelectronics applications. Contrary to the well-known epitaxial (atom by atom) growth of ZnO at low oxygen pressure we use a cluster-assisted synthesis of ZnO films. Gas phase ZnO nanoclusters have been formed during conventional Ultra Violet (λ=193 nm) PLA of sintered ZnO targets into binary, O2/He or O2/Ar, gas mixtures. The role of the first gas is as oxidizing agent and the second one is used for nanocluster cooling and reducing their velocity during condensation and deposition stage.Fundamental aspects of nanoclusters synthesis have been analyzed by reflectron mass spectrometry (MS) and optical time resolved spectroscopy of the laser induced plume together with structural analysis of solid films by X-ray diffraction, HRTEM and AFM microscopy. Optical and lasing properties of films have been studied by conventional photoluminescence and excitation spectroscopy using femtosecond lasers.From MS measurements we show that oxide clusters ZnxOy are already formed in vacuum. Where x is the number of Zn atoms, clusters up to x = 20 have been registered. The concentration of these clusters strongly increase during synthesis in the surrounding gas. We clearly observed four distinct populations: the major one with composition ZnxOx-1 and three minor, oxygen rich, population ZnxOx+1 , ZnxOx+2 and ZnxOx+3 The relative concentration of these initial clusters within the laser induced plume determines the final properties of the film. Using MS and optical time of flight observation of cluster expansion dynamics we discuss the origin of different components of the plume. The total yield of gas formed nanoclusters shows a well pronounced maximum as a function of laser fluence. From all of these results, using the relation between nucleation rate, plume temperature and number of ejected particles, we show a way of optimizing of the deposition process Cluster assisted deposition of ZnO produces homogeneous nanostructured films with cluster size between 5-15 nm , depending on the conditions of the synthesis. All deposits show oriented nanostructures with C axis ┴ to the substrate, where the substrate were electronic grade c-Al2O3, SiO2, Si[111] or Si[100]. ZnO films formed under optimized conditions exhibit excellent optical properties with a narrow exciton luminescence band and a strongly reduced defect green band. Finally we demonstrate room temperature ultraviolet laser emission from nanostructured ZnO. Both excitonexcitonand electron-hole plasma emission regimes were observed