H. Fujisawa

One-dimensional Fe Nanostructures Formed on Vicinal Au(111) Surfaces

In this study of fabricated one-dimensional (1D) nanostructures of Fe adatoms on vicinal Au(111) surfaces, the growth mechanism and electronic structures are investigated by scanning tunneling microscopy (STM) and by angle-resolved photoemission spectroscopy (ARPES). STM observations reveal that dosed Fe atoms are trapped at the lower corners of the steps. They create nucleation centers near the intersections between steps and discommensuration lines, and grow into evenly spaced Fe fragments located at face-centered-cubic (fcc) stacking regions of the substrate. The connection of these fragments aligned along the steps results in the formation of Fe monatomic rows. As the Fe coverage increases, the Fe growth proceeds predominantly at the fcc stacking regions, and forms quasi-1D nanostructures with undulating edges. At an Fe coverage of ∼0.6 ML, the fast-growing parts connect with the adjacent Fe structures and a two-dimensional network structure is built up. ARPES measurements reveal that the decoration o...

Electronic Band Structure of SrCuO2

The energy band structure of a quasi one-dimensional cuprate SrCuO 2 is studied by angle-resolved photoemission spectroscopy and the linear augmented-plane-wave band structure calculation within local density approximation. It was found that the band structure has strongly one-dimensional nature with a finite dispersion along the Cu-O chains. The calculated band structure of SrCuO 2 is in good agreement with the angle-resolved photoemission result except for the region near the Fermi level.

ANGLE-RESOLVED PHOTOEMISSION SPECTROSCOPY OF SRCUO2 : SPIN-CHARGE SEPARATION?

Abstract We have performed angle-resolved photoemission spectroscopy (ARPES) on SrCuO2, which consists of two parallel Cu O chains, to study the “spin-charge separation” in a strongly correlated one-dimensional (1D) system. We observed two dispersive bands in the vicinity of the Fermi level (EF) in the chain direction. One shows a small energy dispersion of about 0.2 eV while the other has a dispersion of more than 0.8 eV. Both have a maximum common point at about 0.9 eV. binding energy atk = π/2 (wherek is the wave vector) in the Brillouin zone. The two dispersive bands may be ascribed to the “spinon” and “holon” bands, respectively, produced through the separation of spin and charge freedoms in the 1D Cu O chain. The experimental result shows good qualitative agreement with the model calculations, but shows quantitative dis-agreement in the intensity of the spinon and holon bands. In the perpendicular direction, we observed a small energy dispersion of about 50 meV with a maximum point atk = π, which indicates a finite interchain interaction in SrCuO2.

Angle-resolved photoemission study of quasi one-dimensional conductor Nb3Te4

Abstract We have performed angle-resolved photoemission spectroscopy on Nb 3 Te 4 , which has zigzag Nb–Nb chains along the c -axis in the crystal. We found a dispersive Nb 4 d band near the Fermi level ( E F ) which crosses E F midway between the center and the boundary of the Brillouin zone in the chain direction. The intensity of the Nb 4 d band was found to be substantially suppressed near/at E F , showing a typical Tomonaga–Luttinger liquid behavior of 1D metals. On the other hand, a clear Fermi-edge cutoff, characteristic of 2D or 3D metals, is seen for this Nb 4 d band. All these results suggest that Nb 3 Te 4 is a quasi 1D metal with admixture of 2D or 3D character due to the finite inter-chain interaction.

Angle-Resolved Photoemission Study of 1D Chain and Two-Leg Ladder

We performed angle-resolved photoemission spectroscopy (ARPES) on Sr2CuO3 and Sr2CuO3 to study the difference of electronic structure between the corner-sharing one-dimensional (1D) chain and the two-leg ladder cuprate. ARPES spectra of Sr2CuO3 show two independent dispersive bands near the Fermi level (EF), which are ascribed to the spinon and the holon band due to the spin-charge separation in the 1D chain. In contrast, ARPES spectra of Sr2CuO3 exhibit only one dispersive band near EF with the periodicity of ladder sublattice, which is assigned to a quasi-particle band where holon and spinon are confined together owing to the opening of the spin gap on the ladder. The present results show a clear difference in the nature of the electronic structure near EF between the Tomonaga—Luttinger liquid (Sr2CuO3) and the Luther—Emery liquid (Sr2CuO24O41).

High-resolution angle-resolved photoemission study of Sr14−xCaxCu2 4O4 1 (x=0 and 6)

Abstract We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) of ladder compounds Sr 14−x Ca x Cu 24 O41 (x= 0 and 6) to study the change of the electronic structure near the Fermi level (E F ) by substitution of Sr with Ca. The experimental band structures of both compounds determined by ARPES show a dispersive band near E F , which has a minimum binding energy at k a = (2n+1)π/2 (n=0, ±1, ±2...) with the periodicity of a ladder sublattice. This result indicates that the electronic states near E F originate in the ladder and from a Mott-Hubbard band with an energy gap at k a = (2n+1)π/2. This suggests that Cu atoms in the ladder take essentially a divalent state (Cu 2+ ) and “self-doped” holes reside on the chain. It was also found that the dispersive band of Sr 8 Ca 6 Cu 24 O 41 is closer to E F than that of Sr 14 Cu 24 O 41 , indicating that the ladder band is “doped” with holes by Ca-substitution. This suggests that the superconductivity observed in a heavily Ca-substituted sample occurs on the ladder.