T. Noda

Resonant tunneling of electrons via 20 nm scale InAs quantum dot and magnetotunneling spectroscopy of its electronic states

The resonant tunneling of electrons through a 20 nm scale InAs quantum dot bound by a pair of very thin AlAs barriers is studied. A well-resolved composite peak resulting from the ground 1s states was observed at 4.2 K in current–voltage characteristics. By investigating the effects of inplane magnetic fields, the shape of the wave function and the spatial extent of the first two electronic states are clarified.

A novel strategy to prepare conducting LB films based on TTF derivatives

Abstract A new method is described for the preparation of conducting Langmuir-Blodgett films based on tetrathialfulvalene (TTF) derivatives without long alkyl chain substitution. The mixed molecular system of behenic acid (BA) and oxygen-substituted TTF-type donor molecules such as 4,5-ethylenedioxy-4′,5′-ethylenedithio-tetrathiafulvalene (EOET) or bis-ethylenedioxy-tetrathiafulvalene (BO) provides a stable bilayer film at the air/water interface. In the LB films prepared by Y-type deposition, the donor molecules form mixed-valence dimers such as D+ D0, without secondary treatments. The maximum conductivities of the LB films reached 1.0S cm−1 (EOET + BA) and 25 S cm−1 (BO + BA) at room temperature. The surface pressure/area isotherms and Fourier transform infra-red spectra are also reported with regard to, respectively, film formation on the water surface and the mixed-valence dimer state under different molar ratios of the donors to B A.

Te 5 p orbitals bring three-dimensional electronic structure to two-dimensional Ir 0.95 Pt 0.05 Te 2

We have studied the nature of the three-dimensional multi-band electronic structure in the twodimensional triangular lattice Ir1-xPtxTe2 (x=0.05) superconductor using angle-resolved photoemission spectroscopy (ARPES), x-ray photoemission spectroscopy (XPS) and band structure calculation. ARPES results clearly show a cylindrical (almost two-dimensional) Fermi surface around the zone center. Near the zone boundary, the cylindrical Fermi surface is truncated into several pieces in a complicated manner with strong three-dimensionality. The XPS result and the band structure calculation indicate that the strong Te 5p-Te 5p hybridization between the IrTe2 triangular lattice layers is responsible for the three-dimensionality of the Fermi surfaces and the intervening of the Fermi surfaces observed by ARPES.

Coexistence of Bloch electrons and glassy electrons in Ca10(Ir4As8)(Fe2- xIrxAs2)5 revealed by angle-resolved photoemission spectroscopy

Angle-resolved photoemission spectroscopy of Ca10(Ir4As8)(Fe2_xIrxAs2)5 shows that the Fe 3d electrons in the FeAs layer form the hole-like Fermi pocket at the zone center and the electron-like Fermi pockets at the zone corners as commonly seen in various Fe-based superconductors. The FeAs layer is heavily electron doped and has relatively good two dimensionality. On the other hand, the Ir 5d electrons are metallic and glassy probably due to atomic disorder related to the Ir 5d orbital instability. Ca10(Ir4As8)(Fe2_xIrxAs2)5 exhibits a unique electronic state where the Bloch electrons in the FeAs layer coexist with the glassy electrons in the Ir4As8 layer.

Recent progress in metallic Langmuir–Blodgett films based on TTF derivatives

Abstract Recent progress in metallic Langmuir–Blodgett (LB) films is reported. First, we review several highly-conducting LB films focusing on the choice of donor molecules, DC conductivity and infrared absorption. From the above, difficulties in the fabrication of metallic LB films based on tetrathiafulvalene (TTF) derivatives are summarized. Among them, it is discussed comparatively that the mixing of an oxygen substituted TTF-type donor bis-ethylenedioxy-tetrathiafulvalene (BEDO-TTF) and behenic acid provides metallic LB films, which clearly exhibit a metallic temperature dependence of DC resistivity without any remarkable trace of percolation at low temperatures.

Intersubband Transition and Electron Transport in Potential-Inserted Quantum Well Structures and their Potentials for Infrared Photodetector

The use of intersubband transition processes in superlattices for the detection of infrared radiations was first proposed and analysed in 1977 by Sakaki and Esaki[1] and later reinvented by Smith and Yariv[2]. As shown in Fig.1, this scheme makes use of the vertical electron transport in a particular miniband structure, where electrons tightly bound in the very narrow ground miniband are photoexcited to an upper miniband of finite width and give rise to photoconductive current. Levine and his coworkers have performed extensive experimental work and successfully demonstrated the effectiveness of this scheme[3,4]. This approach has two attractive features; firstly, its spectral response can be controlled by adjusting the width of minigap. Secondly and more importantly, the mobility of photoexcited electrons for the motion normal to the layer can be set much higher than that in the ground miniband if one chooses properly the widths of two relevant minibands.