Charge-noise-free Lateral Quantum Dot Devices with Undoped Si/SiGe Wafer

We develop quantum dots in a single layered MOS structure using an undoped Si/SiGe wafer. By applying a positive bias on the surface gates, electrons are accumulated in the Si channel. Clear Coulomb diamond and double dot charge stability diagrams are measured. The temporal fluctuation of the current is traced, to which we apply the Fourier transform analysis. The power spectrum of the noise signal is inversely proportional to the frequency, and is different from the inversely quadratic behavior known for quantum dots made in doped wafers. Our results indicate that the source of charge noise for the doped wafers is related to the 2DEG dopant.Comment: Proceedings of the 12th Asia Pacific Physics Conferenc

On the Fertilization of the Triploid Ginbuna

The ferilization process of the gynogenetic triploid ginbuna Carassius auratus langsdorfii were observed histologically. In the triploid female, it has been reported that the sperm nucleus remains in condensed condition throughout the ferilization to first cleavage. This sperm nucleus does not fuse with female pronucleus, producing the all female triploid offsprings gynogenetically. On the other hand, in the present experiment, in some triploid eggs, the penetrated sperm nucleus swells to form male pronucleus. Some of these eggs develop into tetraploid other than triploid fish. On the scale transplantation experiments between these offsprings, in which all of the sperm nuclei had swollen at the time of fertilization, the unidirectional rejection were observed in two combinations. One of these donors was tetraploid and other was triploid. It seems probable that the former unidirectional rejection might be caused by the introduction of paternal genome, and the later might be caused by the recombination of genes at meiosis or the mutation of the donor and/or the host. From these observation, it was ascertained that the offsprings of triploid ginbuna were not always belonging to the same clone but that some of them differenciated their genome during the gametogenesis or early developmental stage.Article信州大学理学部紀要 19(1): 53-61(1984)departmental bulletin pape

Effect of Strain on Room-Temperature Spin Transport in Si₀.₁Ge₀.₉

We report a strain effect on spin transport in semiconductors that exhibit Ge-like conduction bands at room temperature. Using four-terminal nonlocal spin-transport measurements in lateral spin-valve devices, we experimentally estimate the spin diffusion length (λ) of Ge and strained Si₀.₁Ge₀.₉ with two different carrier concentrations. Despite the Ge-like electronic band structure, the obtained λ of a strained Si₀.₁Ge₀.₉ is comparable to that of a Si channel. We discuss a possible mechanism of the strain-induced enhancement of λ at room temperature. As a consequence, we demonstrate the electrical detection of 5-μm lateral spin transport in the strained Si₀.₁Ge₀.₉ by applying an electric field at room temperature.T. Naito, M. Yamada, Y. Wagatsuma, K. Sawano, and K. Hamaya, Effect of Strain on Room-Temperature Spin Transport in Si₀.₁Ge₀.₉, Phys. Rev. Applied, 18, 024005

An Electron-Tracking Compton Telescope for a Survey of the Deep Universe by MeV gamma-rays

Photon imaging for MeV gammas has serious difficulties due to huge backgrounds and unclearness in images, which are originated from incompleteness in determining the physical parameters of Compton scattering in detection, e.g., lack of the directional information of the recoil electrons. The recent major mission/instrument in the MeV band, Compton Gamma Ray Observatory/COMPTEL, which was Compton Camera (CC), detected mere $\sim30$ persistent sources. It is in stark contrast with $\sim$2000 sources in the GeV band. Here we report the performance of an Electron-Tracking Compton Camera (ETCC), and prove that it has a good potential to break through this stagnation in MeV gamma-ray astronomy. The ETCC provides all the parameters of Compton-scattering by measuring 3-D recoil electron tracks; then the Scatter Plane Deviation (SPD) lost in CCs is recovered. The energy loss rate (dE/dx), which CCs cannot measure, is also obtained, and is found to be indeed helpful to reduce the background under conditions similar to space. Accordingly the significance in gamma detection is improved severalfold. On the other hand, SPD is essential to determine the point-spread function (PSF) quantitatively. The SPD resolution is improved close to the theoretical limit for multiple scattering of recoil electrons. With such a well-determined PSF, we demonstrate for the first time that it is possible to provide reliable sensitivity in Compton imaging without utilizing an optimization algorithm. As such, this study highlights the fundamental weak-points of CCs. In contrast we demonstrate the possibility of ETCC reaching the sensitivity below $1\times10^{-12}$ erg cm$^{-2}$ s$^{-1}$ at 1 MeV.Comment: 19 pages, 12 figures, Accepted to the Astrophysical Journa

Nonlinear Conduction by Melting of Stripe-Type Charge Order in Organic Conductors with Triangular Lattices

We theoretically discuss the mechanism for the peculiar nonlinear conduction in quasi-two-dimensional organic conductors \theta-(BEDT-TTF)2X [BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene] through the melting of stripe-type charge order. An extended Peierls-Hubbard model attached to metallic electrodes is investigated by a nonequilibrium Green's function technique. A novel current-voltage characteristic appears in a coexistent state of stripe-type and nonstripe 3-fold charge orders, where the applied bias melts mainly the stripe-type charge order through the reduction of lattice distortion, whereas the 3-fold charge order survives. These contrastive responses of the two different charge orders are consistent with the experimental observations.Comment: 5 pages, 4 figures, to appear in J. Phys. Soc. Jp

Significant effect of interfacial spin moments in ferromagnet-semiconductor heterojunctions on spin transport in a semiconductor

Using controlled ferromagnet (FM) -semiconductor (SC) interfaces in SC-based lateral spin-valve (LSV) devices, we experimentally study the effect of interfacial spin moments in FM-SC heterojunctions on spin transport in SC. First-principles calculations predict that the spin moment of FM-SC junctions can be artificially reduced by inserting 3d transition metal V, Cr, or Cu atomic layers between FM and SC. When all-epitaxial FM-SC Schottky-tunnel contacts with a 0.4-0.5-nm-thick V, Cr, or Cu interfacial layer are formed, we find that the spin signals in FM-SC LSV devices are significantly decreased at 8 K. When we increase the interfacial spin moment by inserting an ∼0.3-nm-thick Co layer between FM and SC, the spin signals at 8 K are significantly enhanced again. From these experiments, we conclude that the interfacial spin moments at FM-SC interfaces are one of the important factors to achieve large spin signals even in SC-based spintronic devices.T. Naito, R. Nishimura, M. Yamada, A. Masago, Y. Shiratsuchi, Y. Wagatsuma, K. Sawano, R. Nakatani, T. Oguchi, and K. Hamaya, Significant effect of interfacial spin moments in ferromagnet-semiconductor heterojunctions on spin transport in a semiconductor, Phys. Rev. B 105, 195308

Phase Diagram of Spinless Fermions on an Anisotropic Triangular Lattice at Half-filling

The strong coupling phase diagram of the spinless fermions on the anisotropic triangular lattice at half-filling is presented. The geometry of inter-site Coulomb interactions rules the phase diagram. Unconventional charge ordered phases are detected which are the recently reported pinball liquid and the striped chains. Both are induced by the quantum dynamics out of classical disordered states and afford extremely correlated metallic states and the particular domain wall-type of excitations, respectively. The disorder once killed by the quantum effect revives at the finite temperature, which is discussed in the terms of the organic $\theta$-ET$_2X$.Comment: 4pages 6figure