We report on the Fermi surface mapping of heavy element crystals using Compton scattering, which has been possible by the recent advent of intense high energy synchrotron radiation sources. Fermi surface mapping provides us insights for long range distortions or charge density waves in crystals. Two examples are shown : The first one is Fermi surface mapping of the η-Mo4O11 low-dimensional conductor. A clear nesting vector is observed in the Fermi surfaces that have experimentally been obtained. The second example is Fermi surface study of Ba1-xKxBiO3. A clear feature of the Fermi surface nesting is observed across the transition between the distorted (insulating) and non-distorted (metallic) phases.
X-ray magnetic circular dichroism (XMCD) is a powerful tool for studying the electronic and magnetic states in ferromagnetic materials. Beamline 39XU at SPring-8 has currently developed the material science using XMCD under high pressures. Here, we briefly review the experimental techniques and the recent outcome of the pressure-dependent XMCD in ferromagnetic Fe, Co, and Ni metals and itinerant ferromagnetic Mn3GaC. The extension to the experiment under multiple extreme conditions, i.e. low temperature, high magnetic field, and high pressure, is also prospected.
The eukaryotic GINS complex is essential for the establishment of DNA replication forks and replisome progression. We report the crystal structure of the human GINS complex. The heterotetrameric complex adopts a pseudo symmetrical layered structure comprising two heterodimers, creating four subunit-subunit interfaces. The structural and biochemical data suggest that the tetrameric complex ensures a stable platform for the C-terminal domain of Psfl to act as a key interaction interface for other proteins in the replication-initiation process.
We have developed a nondestructive analysis method, which is named X-ray reciprocallattice space imaging, based on synchrotron diffraction for quickly characterizing a crystalline nanometer-scale structure in a non-vacuum environment. The basic idea behind the method is that the reciprocal lattice of 1 D or 2D structures are an array of sheets or rods, respectively. Thus the reciprocal-lattice space can be recorded for a fixed sample with a 2D X-ray detector fixed. We successfully demonstrated that the method was applicable to structural evaluation of ultrathin NiO wires on a sapphire surface in air, Bi nanolines buried in Si, an interfacial structure of a Au electrode in solution, and a thinfilm of Bi4Ti3O12.
The variation of the superstructure related to the charge/orbital ordering in layered manganites RE0.5 (Ca1-ySry) 1.5MnO4 (RE = Pr or Eu) has been systematically investigated by lowtemperature transmission electron microscopy (TEM), It is found that the superstructure is collapsed as increasing (1) the average ionic radius (rA) of A-site cations or enhancing (2) the quenched disorder by the substituting Sr for Ca. The results indicate that the electronic phase of the single layered manganites is controlled not only by the average ionic radius of A-site, but also by the quenched disorder ascribed as the variance in A-site ionic radii (σ2 = Σixiri2-rA2) .
Manipulation of magnetic states in ferromagnetic materials using spin-polarized current has attracted much attention because of a wide range of possible spintronic applications. For well controlled magnetic domain manipulation, we microscopically investigate the current-excited magnetization dynamics in narrow Permalloy wires by means of Lorentz microscopy and electron holography, together with the results of simultaneous transport measurements. Current pulses are found to induce a variety of magnetization dynamics below the Curie temperature and a detailed structural evolution of the magnetization is presented as a function of applied current density. We discuss probable mechanism of observed features of the current-excited magnetization dynamics.