Infrared spectroscopy techniques for studying the electronic structures of materials under high-pressure

In this article, we describe our high-pressure infrared (IR) spectroscopy techniques for studying the electronic structures of materials at high pressures. High pressure of up to 20 GPa is applied to a sample using a diamond anvil cell (DAC). To accurately perform IR spectroscopy in the limited sample space of a DAC, synchrotron radiation is used as a bright IR source. Our techniques allow reflectance studies of a single crystal sample and determination of the optical functions of the sample such as dielectric function and optical conductivity. To illustrate the capability and usefulness of our techniques, some actual results of high-pressure IR studies on rare-earth compounds are described

Optical Conductivity Study of f Electron States in YbCu2Ge2 at High Pressures to 20 GPa

Optical conductivity [σ(ω)] of YbCu2Ge2 has been measured at external pressures (P) to 20 GPa, to study the P evolution of f electron hybridized states. At P=0, σ(ω) shows a marked mid-infrared (mIR) peak at 0.37 eV, which is due to optical excitations from f14 (Yb2+) state located below the Fermi level. With increasing P, the mIR peak shows significant shifts to lower energy, reaching 0.18 eV at P=20 GPa. This result indicates that the f14 energy level increases toward the Fermi level with P. Such a shift of the f electron level with P has been expected from theoretical considerations, but had never been demonstrated by spectroscopic experiment under high P. The obtained results are also analyzed in terms of the P evolution of the conduction-f electron hybridization

Metallic Pattern Fabrication in Organic Mott Insulating Crystal by Local X-Ray Irradiation

We have fabricated a metallic structure in an organic Mott insulator $\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Cl. The periodic metallic domains of approximately 90$\times$90 $\mu$m$^2$ obtained by X-ray irradiation through a molybdenum mesh mask are visualized by scanning microregion infrared reflectance spectroscopy technique. No deterioration by irradiation is found in a range of nanometer to micrometer scales. We demonstrate that the present processing method is applicable for the fabrication of molecular electronic devices.Comment: 3 pages, submitted to APE

Importance of individual events in temporal networks

Records of time-stamped social interactions between pairs of individuals (e.g., face-to-face conversations, e-mail exchanges, and phone calls) constitute a so-called temporal network. A remarkable difference between temporal networks and conventional static networks is that time-stamped events rather than links are the unit elements generating the collective behavior of nodes. We propose an importance measure for single interaction events. By generalizing the concept of the advance of event proposed by [Kossinets G, Kleinberg J, and Watts D J (2008) Proceeding of the 14th ACM SIGKDD International conference on knowledge discovery and data mining, p 435], we propose that an event is central when it carries new information about others to the two nodes involved in the event. We find that the proposed measure properly quantifies the importance of events in connecting nodes along time-ordered paths. Because of strong heterogeneity in the importance of events present in real data, a small fraction of highly important events is necessary and sufficient to sustain the connectivity of temporal networks. Nevertheless, in contrast to the behavior of scale-free networks against link removal, this property mainly results from bursty activity patterns and not heterogeneous degree distributions.Comment: 36 pages, 13 figures, 2 table

クラスター : 一固体表面衝突の動的過程

東京都立大学, 1993-03-25, 博士（理学）, 甲第310

Probing Structural Perturbation in a Bent Molecular Crystal with Synchrotron Infrared Microspectroscopy and Periodic Density Functional Theory Calculations

The range of unit cell orientations generated at the kink of a bent single crystal poses unsurmountable challenges with diffraction analysis and limits the insight into the molecular-scale mechanism of bending. On a plastically bent crystal of hexachlorobenzene, it is demonstrated here that spatially resolved microfocus infrared spectroscopy using synchrotron radiation can be applied in conjunction with periodic density functional theory calculations to predict spectral changes or to extract information on structural changes that occur as a consequence of bending. The approach reproduces well the observed trends, such as the wall effects, and provides estimations of the vibrational shifts, unit cell deformations, and intramolecular parameters. Generally, expansion of the lattice induces red-shift while compression induces larger blue-shift of the characteristic ν­(C–C) and ν­(C–Cl) modes. Uniform or non-uniform expansion or contraction of the unit cell of 0.1 Å results in shifts of several cm^–1, whereas deformation of the cell of 0.5° at the unique angle causes shifts of <0.5 cm^–1. Since this approach does not include parameters related to the actual stimulus by which the deformation has been induced, it can be generalized and applied to other mechanically, photochemically, or thermally bent crystals