Hiroyoshi Ishii

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.

Anomaly of X-ray Diffraction Profile in Single-Walled Carbon Nanotubes

X-ray diffraction (XRD) studies on single-walled carbon nanotube (SWNT) samples prepared by the arc-discharge method were reported. The XRD profile was basically explained to be a result of triangular packing of SWNTs with a lattice constant of 17.1 A and an average nanotube radius of 7.1 A. We found an anomalous change in XRD profiles before and after heat-treatment of the SWNT samples in air at ~350°C. Combined with gravimetric measurements and resistivity measurements, a detailed simulation of the XRD profiles showed that air (oxygen, and/or nitrogen and/or water) can be condensed inside the SWNTs.

Threshold Singularities of p-shell Absorption in Potassium, Rubidium and Cesium Metals

The extreme ultraviolet absorption spectra of K, Rb, and Cs show spikes at the thresholds of outermost- p -shell absorption. With inclusion of the data on Nareported by Haensel et al. , it is concluded that the occurrence of a spike at the edge of the absorption spectrum of outermost- p -shell electrons is a commoncharacteristic of alkali metals. In Rb and Cs no definite spike is found at the onset of the high-energy-component-absorption, L II , produced by the spin-orbit splitting of the levels of core holes. The sharpness of the spike decreases in the order of Na, K, Rb, and Cs. The threshold exponent α 0 for the transition to the s -symmetric state, obtained by neglecting the contribution from the transition to the d -symmetric state, decreases as the electron gas parameter, r s , increases in contrast with the prediction from the electron gas theory.

X-Ray Photoemission Spectroscopy of Nd2-xCexCuO4-y and La2-xSrxCuO4

We have measured the Cu 2p and O 1s X-ray photoemission spectra of the high-Tc superconductors Nd2-xCexCuO4-y and La2-xSrxCuO4, and the copper oxides CuO and Cu2O. The Cu 2p spectra of superconductors show features similar to those of CuO with divalent Cu ions. For Nd2-xCexCuO4-y, the intensity ratio of the satellite to the main peaks decreases with increasing Ce content. The O 1s spectra exhibit a single-peaked structure and are insensitive to whether either electron or hole is doped.

Gas Storage in Single-Walled Carbon Nanotubes

Abstract X-ray diffraction (XRD) and electrical resistance measurement on single-walled carbon nan-otube (SWNT) samples prepared by the arc-discharge method are reported. The XRD profile of heat-treated sample indicated that air (oxygen, and/or nitrogen and/or water) can be condensed inside the SWNTs. We also found that the electrical resistance of SWNT soot is significantly affected by exposing to the oxygen gas and humid air.

Temperature-dependent change of correlated electronic states in Yb4As3 and Yb4(As1-xSbx)3 probed by high resolution photoemission spectroscopy

Clear changes of the Yb 4f photoemission spectra with temperature are observed in Yb 4 As 3 by high resolution photoemission spectroscopy. The photoemission intensity is very low at the Fermi level and decreases as the temperature is lowered in accord with the narrowing of the 4f spectra. Bulk and surface contributions are deconvoluted in the 4f 13 final state spectra. In comparison with the corresponding results in Yb 4 (As 1- x Sb x ) 3 , the spectral changes of Yb 4 As 3 with temperature are confirmed to be beyond simple thermal broadening effects and related to the charge ordering effects. Although the change from the charge ordering temperature ( T t ) down to about T t /2 is consistent with a theoretical prediction, the change below it is rather unusual and may be ascribed to the incompleteness of the charge ordering effect. Spectral changes with Yb 4 Sb 3 -substitution are qualitatively discussed.

Effects of Ce Doping on Electronic Structures of Ln2-xCexCuO4 (Ln=Nd, Sm, Eu, Gd) Studied by Core-Level Photoemission Spectroscopy

We have investigated the changes in the electronic structures of Ln2-xCexCuO4 (Ln=Nd, Sm, Eu and Gd) upon Ce doping using core-level X-ray photoemission spectroscopy. For Ln2-xCexCuO4, the O 1s spectra exhibit a single-peaked structure. The energy positions of the O 1s lines are shifted toward the high binding energy side with increasing Ce concentration. For the Cu 2p spectra, the intensity ratio of the satellite to the main peaks decreases with increasing Ce concentration. This decrease can be explained by the presence of Cu1+ under Ce doping.

Photoemission Study of 4f Electronic States in PrFe4P12 and Related Pr Compounds

We have measured the Pr 4 d –4 f high-resolution resonant photoemission and the Pr 3 d core-level photoemission spectra of PrFe 4 P 12 and related compounds PrSn 3 , PrAl 2 and Pr metal. The Pr 4 f...

Vacuum Ultraviolet Absorption Spectra of La, Ce, Sm, Eu and Gd Metals

Optical absorption coefficients of La, Ce, Sm, Eu and Gd metals have been measured in the photon energy range from 6 to 40 eV. Contribution of the 4 f electrons to the optical absorption has not been observed in the present photon energy region. The 5 p threshold of Ce, Sm, Eu and Gd does not show sharp absorption edge. The rounded edge indicates that the size of the 5 p core hole should be larger than that in heavy simple alkali metals.

Local magnetic susceptibility in rare-earth compounds

The element specific magnetic susceptibilities of some rare-earth compounds are estimated by measuring magnetic circular dichroism at rare-earth M 4,5 absorption edges. The temperature dependences ...