Bosonization for disordered and chaotic systems

Using a supersymmetry formalism, we reduce exactly the problem of electron motion in an external potential to a new supermatrix model valid at all distances. All approximate nonlinear sigma models obtained previously for disordered systems can be derived from our exact model using a coarse-graining procedure. As an example, we consider a model for a smooth disorder and demonstrate that using our approach does not lead to a "mode-locking" problem. As a new application, we consider scattering on strong impurities for which the Born approximation cannot be used. Our method provides a new calculational scheme for disordered and chaotic systems.     

Mössbauer study of the transition metal phosphorus trichalcogenide FePS3 and spin glass Mn0.5Fe0.5PS3

The transition metal phosphorus trichalcogenides MnPS₃ and the FePS₃ are CdCl₂ type layered compounds, where the transition metal ions form a hexagonal lattice. While these compounds order anti-ferromagnetically at low temperature, the magnetic structures are different. We have reported that these mixtures Mn_0.5Fe_0.5PS₃ is a spin glass with a glass transition temperature T _g=33.7 K. Then, in this work, we report that the results of the temperature variation of the ⁵⁷Fe Mössbauer spectra of FePS₃ and Mn_0.5Fe_0.5PS₃, in detail. In the anti-ferromagnetic state of FePS₃, the hyperfine magnetic field H _int increases with decreasing temperature and the Isomer shift I. S. increases slightly with decreasing temperature. However in Mn_0.5Fe_0.5PS₃, the two broadened peaks are observed and the two peaks became a single peak with decreasing temperature at about 50.0 K, which is higher than T _g=33.7 K. In the spin glass Mn_0.5Fe_0.5PS₃, the Mössbauer spectra suggest that the magnetic interactions exist far above T _g.     

Phase transition behavior and proton conduction mechanism in cesium hydrogen sulfate/silica composite

Proton conduction and crystal structure in CsHSO₄/SiO₂ composite composed of polycrystalline CsHSO₄ and mesoporous silica particles were investigated based on conductivity measurement and characterizations using Raman spectroscopy, XRD, and differential thermal analysis. The conductivity of pure CsHSO₄ abruptly changes at around 414 K (superprotonic phase transition), being accompanied with the structural transformation from a monoclinic phase to a tetragonal phase, while the conductivity of CsHSO₄/SiO₂ composite is significantly larger by over three orders of magnitude than that of pure CsHSO₄ below the critical temperature of the superprotonic phase transition (353-414 K). Raman spectroscopy and XRD indicate that this remarkable conductivity-enhancement in the composite is not due to the stabilization of the tetragonal phase (superprotonic phase) below its critical temperature. The line-broadening of the internal modes in the Raman spectra suggests that the rapid reorientational motion of the HSO₄⁻ ion, which leads to superprotonic conduction, is induced in the composite even below the critical temperature. The reorientational motion of the HSO₄⁻ ion below the critical temperature will occur at the interfacial phase which is structurally disordered and forms between CsHSO₄ and SiO₂ in the mesopores and/or on the surfaces of silica particles. Proton transfer will be accelerated via the interfacial conduction-pathway in the composite.     

Fermi surface evolution and Luttinger theorem in Na(x)CoO2: a systematic photoemission study

We report a systematic angle-resolved photoemission study on Na(x)CoO2 for a wide range of Na concentrations (0.3 < or = x < or = 0.72). In all the metallic samples at different x, we observed (i) only a single holelike Fermi surface centered around gamma and (ii) its area changes with x according to the Luttinger theorem. We also observed a surface state that exhibits a larger Fermi surface area. The e'(g) band and the associated small Fermi surface pockets near the K points predicted by band calculations are found to sink below the Fermi energy in a manner almost independent of the doping and temperature.     

Anomalous momentum dependence of the superconducting coherence peak and its relation to the pseudogap of La1.85Sr0.15CuO4

We performed high-resolution angle-resolved photoemission spectroscopy on La1.85Sr0.15CuO4 to study the nature of the single-particle excitation gap. We found that there is a well-defined superconducting coherence peak in the off-nodal region while it is strongly suppressed around the antinode. The momentum dependence of the single-particle excitation gap shows a striking deviation from the dx-y2--wave symmetry with anomalous enhancement around the antinode in both the superconducting and the pseudogap state. The observed close correlation between the superconducting coherence peak and the pseudogap suggests a substantial contribution of the pseudogap to the anomalous behavior of the gap in the superconducting state.     

Study for noise reduction in synchrotron radiation based scanning tunneling microscopy by developing insulator-coat tip

To solve difficulties of instability and inaccuracy in synchrotron radiation based scanning tunneling microscopy, a method to reduce noise was investigated. New insulator-coat tips were developed to shut out electrons coming from a wide area that damage the spatial resolution. By changing the exposed conductive area at the end of the insulator-coat tips, the effect of noise reduction was estimated. The tip with an exposure area of 50 nm in diameter was found to reduce noise effectively. Also a key discriminating condition was found to obtain the local signal, which is based on the modulation of the X-ray-induced tip current caused by excitation of the specific element.     

Inflation model with lower multipoles of the CMB suppressed

The recent observation of the cosmic microwave background anisotropy by the WMAP confirmed that the lower multipoles are considerably suppressed. From the standpoint of the cosmic variance, it is nothing but a statistical accident. Alternatively, one can attribute the deficit of fluctuation on the large scale to the cosmic history, which might be explained in the context of the inflationary physics. In this Letter, we show that it is possible to explain the suppressed lower multipoles in the hybrid new inflation model.     

Nano-crater formation on a Si(1 1 1)-(7 × 7) surface by slow highly charged ion-impact

Using scanning tunneling microscopy (STM) and time of flight secondary ion mass spectrometry (TOF/SIMS), we observed radiation effects on a Si(1 1 1)-(7 × 7) surface in the collision of a single highly charged ion (HCI) with a charge state q up to q = 50. The STM observation with atomic resolution revealed that a nanometer sized crater-like structure was created by a single HCI impact, where the size increased rapidly with q. The secondary ion yields also increased with q in which multiply charged Si ions (Siⁿ⁺) were clearly observed in higher q HCI-collisions. The sputtering mechanism is briefly discussed, based on the so-called Coulomb explosion model.     

Supercurrent pumping in Josephson junctions with a half-metallic ferromagnet

A Josephson current through a half-metallic ferromagnet between two conventional superconductors is theoretically studied. The spin dynamics such as magnon excitation plays a crucial role not only for the conversion between spin-singlet and spin-triplet pairs but also for the formation of the composite state of a triplet Cooper pair and magnon, by which the Josephson current flows between the superconductors. We propose the supercurrent pumping driven by the coherent precession of the magnetization by tuning the microwave frequency to the ferromagnetic resonance frequency in a ferromagnetic Josephson junction.