Tsuneaki Miyahara

Direct observation of Tomonaga-Luttinger-liquid state in carbon nanotubes at low temperatures.

The electronic transport properties of conventional three-dimensional metals are successfully described by Fermi-liquid theory. But when the dimensionality of such a system is reduced to one, the Fermi-liquid state becomes unstable to Coulomb interactions, and the conduction electrons should instead behave according to Tomonaga–Luttinger-liquid (TLL) theory. Such a state reveals itself through interaction-dependent anomalous exponents in the correlation functions, density of states and momentum distribution of the electrons. Metallic single-walled carbon nanotubes (SWNTs) are considered to be ideal one-dimensional systems for realizing TLL states. Indeed, the results of transport measurements on metal–SWNT and SWNT–SWNT junctions have been attributed to the effects of tunnelling into or between TLLs, although there remains some ambiguity in these interpretations. Direct observations of the electronic states in SWNTs are therefore needed to resolve these uncertainties. Here we report angle-integrated photoemission measurements of SWNTs. Our results reveal an oscillation in the π-electron density of states owing to one-dimensional van Hove singularities, confirming the one-dimensional nature of the valence band. The spectral function and intensities at the Fermi level both exhibit power-law behaviour (with almost identical exponents) in good agreement with theoretical predictions for the TLL state in SWNTs.

Performance of a very high resolution soft x-ray beamline BL25SU with a twin-helical undulator at SPring-8

We report on the excellent performance of a newly constructed soft x-ray helical undulator beamline BL25SU of SPring-8 for photon energies 500–1800 eV. The full beamline was designed to perform very high resolution soft x-ray spectroscopy of solids with using high brilliance, highly circularly polarized undulator radiation. The grazing incidence monochromator employs varied-line-spacing plane gratings which operate in convergent light from a spherical mirror and focuses monochromatic light onto the exit slit. A resolving power in excess of 15 000 was measured at 540 and 870 eV for a grating with a central groove density of 600 lines/mm from the photoemission spectra of Au. A resolving power of more than 20 000 is estimated near 870 eV for a grating with a central groove density of 1000 lines/mm. A photon flux of more than 1×1011 photons/s/100 mA/0.02% b.w. is supplied onto the sample between 500 and 1800 eV with very low amount of higher-order light. The low heat load from the twin-helical undulator gives...

Optical Spectra of Y2O3 Single Crystals in VUV

Optical absorption in the tail region and reflectivity at room temperature in the VUV region up to 42 eV are measured on Y 2 O 3 single crystals. Various optical constants as functions of photon energy are derived therefrom by use of the Kramers-Kronig relation. The Urbach rule parameters are also determined experimentally for the tail. A tentative interpretation is given on the spectral structures found in the optical constants, referring to the energy levels of Y 2+ and Y 3+ free ions.

Strong Circular Dichroism in Photoelectron Diffraction from Nonchiral, Nonmagnetic Material–Direct Observation of Rotational Motion of Electrons

Strong circular dichroism is found in 2-dimensional angular distribution patterns of the Si 2p photoelectrons from the Si(001) surface, which has no chirality and magnetism. The forward focusing peaks in the pattern rotate clockwise or counterclockwise when the helicity of the incident circularly polarized light is reversed. These rotations of the pattern are explained by rotational motion of photoelectrons around the nuclei. This is the first direct observation of the rotational motion of the electrons and clarifies the correspondence between the classical and the quantum mechanical ideas of angular momentum.

Twin helical undulator beamline for soft X-ray spectroscopy at SPring-8

A very high resolution soft X-ray beamline, BL25SU, has been designed and is under construction at SPring-8. Completely right or left circularly polarized light is supplied on a common axis of a newly designed twin helical undulator. A helicity modulation up to 10 Hz can be performed using five kicker magnets. The fundamental radiation covers the region 0.5-3 keV. Higher-order radiation is rather weak on the axis. A monochromator with varied-line-spacing plane gratings is installed to cover the region below 1.5 keV. A very high resolution beyond 10(4) is expected for the whole energy region.

Solid surface analysis beamline BL‐1A at the Photon Factory

The characteristics of the beamline used for PES (photoelectron spectroscopy) and SEXAFS (surface extend x‐ray absorption fine structure) studies at the Photon Factory are described. Monochromatic photons are available in the energy range between 50–900 and 2500–4000 eV. This has been accomplished using a grating/crystal monochromator with a combination of two paraboloidal mirrors. The synchrotron radiation is focused by a set of paraboloidal mirrors at a 1.0° incident grazing angle. The plane grating/mirror combination has covered vacuum ultraviolet region of 50–900 eV with 1200 and 2400 g/mm gratings. The InSb (111) double crystals have covered soft x‐ray region of 2500–4000 eV. The performance of the gratings in respect to intensity, resolution, and the effect of ‘‘on blaze operation’’ is discussed. The Bragg peak searching system in crystal mode and its performance are also described. With the use of InSb(111) crystals, the energy range below 2700 eV will be covered with precise roll adjustment of bot...

Investigation of carbon contamination of synchrotron radiation mirrors

Abstract Carbon-contaminated synchrotron radiation mirrors have been successfully cleaned by a dc glow discharge in oxygen. Reflectance and angle-resolved scattering have been measured before and after cleaning. The effect of carbon contamination on reflectance is severe at near normal incidence whereas it is small at grazing incidence. The decrease in reflectance is most noticeable for photons with an energy below about 10 eV. In the discharge arrangement in which the mirror surface did not face an electrode, the reflectance of contaminated mirrors was nearly restored to that of uncontaminated mirrors and the scattering level was reduced. An additional discharge, in which the mirror surface faced the electrode, degraded the reflectance but produced no appreciable change in the scattering level.

Low-Energy Electronic Structure of the Kondo Insulator YbB12

We have studied the low-energy electronic structure of a Kondo insulator YbB{sub 12} by high-resolution photoemission spectroscopy. A {open_quote}{open_quote}Kondo peak{close_quote}{close_quote} is observed {approximately}25 meV below the Fermi level, which agrees well with the Kondo temperature, whereas the gap at the Fermi level is found much smaller, indicating that the magnetic properties at higher temperatures (75 K) are indeed determined by the Kondo effect in spite of the gap formation at lower temperatures. A renormalized band picture is presented to describe the coexistence of the Kondo peak and the transport gap as well as the highly asymmetric line shape of the Kondo peak. {copyright} {ital 1996 The American Physical Society.}

A New Constant Deviation Monochromator for Angle Resolved Photoemission Spectroscopy

A new type of constant deviation monochromator equipped with three interchangeable concave gratings (600, 1200 and 2400 grooves/mm) of 2 m radius of curvature was designed and built specifically for angle resolved photoemission spectroscopy at photon energies ranging from 20 to 160 eV. The exit slit of the monochromator is at a fixed position, whereas the entrance slit moves, simultaneously with grating rotation, along the direction of the incident light so as to minimize the amount of defocusing. A monochromatic light spot of 0.5 mm in diamter was obtained at the fixed sample position with the aid of a toroidal postfocussing mirror. It is found over the energy range concerned that the resolution is bettern than 1700 with 25 µm slits, and the photon flux obtained behind the toroidal mirror for a horizontal acceptance angle 0.5 mrad is 4×1010 photons/s when the width of the slits is 50 µm and the stored current for synchrotron radiation is 100 mA.

Low-Energy Electronic Structure of the Kondo Insulator YbB{sub {bold 12}}

We have studied the low-energy electronic structure of a Kondo insulator YbB{sub 12} by high-resolution photoemission spectroscopy. A {open_quote}{open_quote}Kondo peak{close_quote}{close_quote} is observed {approximately}25 meV below the Fermi level, which agrees well with the Kondo temperature, whereas the gap at the Fermi level is found much smaller, indicating that the magnetic properties at higher temperatures (75 K) are indeed determined by the Kondo effect in spite of the gap formation at lower temperatures. A renormalized band picture is presented to describe the coexistence of the Kondo peak and the transport gap as well as the highly asymmetric line shape of the Kondo peak. {copyright} {ital 1996 The American Physical Society.}