The spatial charge arrangement of a typical quasi-two-dimensional organic conductor α-(BEDT-TTF) 2 I 3 is revealed by single crystal structure analysis using synchrotron radiation. The results show that the horizontal stripe type structure, which was suggested by mean field theory, is established. We also find the charge disproportion above the metal-insulator transition temperature and a significant change in transfer integrals caused by the phase transition. Our result elucidates the insulating phase of this material as a 2k F charge density localization.KEYWORDS: α-(BEDT-TTF)2I3, Charge Ordering, Quasi two dimensional organic conductor, Synchrotron Radiation, Crystal structure analysisAs an origin of a metal-insulator (M-I) transition, the charge ordering caused by the long rangeCoulomb interaction between electrons is a prominent phenomenon as well as the Peierls transition or the Mott Hubbard transition. Organic materials having low-dimensionality provide us a field of studying such interesting phenomena. 1 Among them, an organic conductor α-(BEDT-TTF) 2 I 3 , which undergoes a M-I transition at T M I = 135 K, 2 attracts considerable attention because of its possibility of zero-gap semiconductor under hydrostatic pressures. 3 The insulating phase is a nonmagnetic state with a spin gap, 4 and interpreted to be caused by a charge disproportionation theoretically 5, 6 and experimentally. 7,8 According to these studies, horizontal-charge stripes with valences of +1e and 0 are expected on BEDT-TTF molecules while no structural evidence has been reported. In this letter, we report a precise structure of α-(BEDT-TTF) 2 I 3 as a function of temperature based on synchrotron radiation diffraction measurements in order to provide evidence of the charge disproportionation.α-(BEDT-TTF) 2 I 3 , which has a two-dimensional (2D) conduction band, is a typical organic conductor made of I − 3 ions and BEDT-TTF 0.5+ on average. The crystal structure of this material is a sandwich structure of I 3 insulating layers and 2D-BEDT-TTF conduction layers having a quarterfilled hole band. The space group at room temperature is P1. Together with the metal-insulator transition, it shows paramagnetic-nonmagnetic transition. 4 According to several reports, 6, 9, 10 this transition is not a Peierls transition but a charge ordering caused by a strong Coulomb repulsion.

Antiferroquadrupolar (AFQ) ordering has been conjectured in several rare-earth compounds to explain their anomalous magnetic properties. No direct evidence for AFQ ordering, however, has been reported. Using the resonant x-ray scattering technique near the Dy L(III) absorption edge, we have succeeded in observing the AFQ order parameter in DyB2C2 and analyzing the energy and polarization dependence. The much weaker coupling between the orbital degrees of freedom and the lattice in 4f electron systems than in 3d compounds makes them an ideal platform to study orbital interactions originating from electronic mechanisms.

Under zero magnetic field, a quadrupolar order parameter at q Q = ( 1 2 , 1 2 , 1 2 ) in a typical antiferro-quadrupole (AFQ) ordering compound CeB 6 has been observed for the first time by means of a resonant X-ray scattering (RXS) technique. The RXS is observed at the 2p → 5d dipole transition energy of the Ce L 3 -edge. Using this RXS technique to observe the pure order parameter of the AFQ state, the magnetic phase diagram of Phase II is first determined.

Nanotubes are generally prepared from their constituent elements at high temperatures, and thus it is difficult to control their size, shape and electronic states. One useful approach for synthesizing well-defined nanostructures involves the use of building blocks such as metal ions and organic molecules. Here, we show the successful creation of an assembly of infinite square prism-shaped metal-organic nanotubes obtained from the simple polymerization of a square-shaped metal-organic frame. The constituent nanotube has a one-dimensional (1D) channel with a window size of 5.9×5.9 Å(2), and can adsorb water (H(2)O) and alcohol vapours, whereas N(2) and CO(2) do not adhere. It consists of four 1D covalent chains that constitute a unique electronic structure of 'charge-density wave (CDW) quartets' on crystallization. Moreover, exchanging structural components and guest molecules enables us to control its semiconductive bandgap. These findings demonstrate the possibility of bottom-up construction of new porous nanotubes, where their degrees of freedom in both pore space and framework can be used.

Synchrotron x-ray-diffraction experiments have been carried out in a perovskite-type vanadium oxide YVO 3 to elucidate orbital ordering of the system. The change from C-to G-type orbital ordering at the lower magnetic transition temperature was strongly suggested. The long-range orbital ordering appears also in the high-temperature paramagnetic phase. Azimuthal-angle dependence of orbital superlattice reflections indicates that for both orbital-ordering phases the orbital occupation is approximately the d xy 1 d yz 1 and d xy 1 d zx 1 configuration in two sublattices, respectively. These results are in good agreement with a theoretical prediction.

Using a surface x-ray diffraction technique, we investigated the atomic structure of two types of interfaces between LaAlO3 and SrTiO3, that is, p-type (SrO/AlO2) and n-type (TiO2/LaO) interfaces. Our results demonstrate that the SrTiO3 in the sample with the n-type interface has a large polarized region, while that with the p-type interface has a limited polarized region. In addition, atomic intermixing was observed to extend deeper into the SrTiO3 substrate at the n-type interface compared to the p type. These differences result in distinct degrees of band bending, which likely contributes to the striking contrast in electrical conductivity between the two types of interfaces.

The origin of a room-temperature magnetoelectric (ME) effect has been examined by means of neutron powder diffraction measurements for a Z-type hexaferrite Sr(3)Co(2)Fe(24)O(41). The temperature and magnetic-field dependence of the electric polarization P and several magnetic Bragg reflections show that a commensurate magnetic order with a (0,0,1) propagation vector has an intimate connection with the ME effect. The room-temperature ME effect can be understood in terms of the appearance of P which is induced by a transverse conical spin structure through the inverse Dzyaloshinskii-Moriya mechanism in analogy with Y-type hexaferrites.

Resonant X-ray diffraction (RXD) uses X-rays in the vicinity of a specific atomic absorption edge and is a powerful technique for studying symmetry breaking by motifs of various multipole moments, such as electric monopoles (charge), magnetic dipoles (spin) and electric quadrupoles (orbital). Using circularly polarized X-rays, this technique has been developed to verify symmetry breaking effects arising from chirality, the asymmetry of an object upon its mirroring. Chirality plays a crucial role in the emergence of functionalities such as optical rotatory power and multiferroicity. Here we apply spatially resolved RXD to reveal the helix chirality of Dy 4f electric quadrupole orientations and its domain structure in DyFe3(BO3)4, which shows a reversible phase transition into an enantiomorphic space-group pair. The present study provides evidence for a helix chiral motif of quadrupole moments developed in crystallographic helix chirality.