Room-temperature detection of spin accumulation in silicon across Schottky tunnel barriers using a MOSFET structure

Using a metal-oxide-semiconductor field effect transistor (MOSFET) structure with a high-quality CoFe/n^+Si contact, we systematically study spin injection and spin accumulation in a nondegenerated Si channel with a doping density of ~ 4.5*10^15cm^-3 at room temperature. By applying the gate voltage (V_G) to the channel, we obtain sufficient bias currents (I_Bias) for creating spin accumulation in the channel and observe clear spin-accumulation signals even at room temperature. Whereas the magnitude of the spin signals is enhanced by increasing I_Bias, it is reduced by increasing V_G interestingly. These features can be understood within the framework of the conventional spin diffusion model. As a result, a room-temperature spin injection technique for the nondegenerated Si channel without using insulating tunnel barriers is established, which indicates a technological progress for Si-based spintronic applications with gate electrodes.Comment: 7 pages, 6 figure

Dynamic Evolution of Flux Distributions in a Pulse-driven Superconductor by High-speed Magneto-optical Imaging

The accurate understanding of flux dynamics is essential for the design and operation of superconducting circuits. The time evolution of flux-density distribution in an NbN strip by the transport current was observed using high-speed magneto-optical microscopy. It was determined that even for the dynamic penetration and exclusion of vortices under the transport current, the surface barrier is essential. This feature is important for the correct understanding of the complex behavior of state-of-the-art superconducting devices

NMR measurements on obliquely evaporated Co-Cr films

The distribution of the hyperfine fields or the resonance frequencies in metals and alloys obtained by NMR measurements have been known for a long time. Recently, new experimental data have been published about thin films for studying their chemical inhomogeneities. An example is the study on sputtered and evaporated Co-Cr layers. In this paper we report on the compositional distribution of co-evaporated Co-Cr films by using the Co spin-echo NMR technique. For comparison single source evaporated samples of Co-Cr and pure Co as well as two alloyed ribbons (¿bulk¿ samples) have also been measured. Based on the NMR results the local Cr concentration of the ferromagnetic and less ferromagnetic regions are determined. In comparison the data from the co-evaporated films, even at low substrate temperature, have clearly shown the presence of a process-induced compositional separation. This is in qualitative agreement with the magnetic properties of the samples

Canonical treatment of two dimensional gravity as an anomalous gauge theory

The extended phase space method of Batalin, Fradkin and Vilkovisky is applied to formulate two dimensional gravity in a general class of gauges. A BRST formulation of the light-cone gauge is presented to reveal the relationship between the BRST symmetry and the origin of $SL(2,R)$ current algebra. From the same principle we derive the conformal gauge action suggested by David, Distler and Kawai.Comment: 11 pages, KANAZAWA-92-1

Study of the K+K- Interaction at COSY-11

In this article we present studies of the near threshold pp-->ppK+K- reaction in view of the K+K- final state interaction. The investigations include analysis of both the low-energy K+K- invariant mass distributions measured by COSY-11 collaboration at excess energies of Q = 10 MeV and Q = 28 MeV and the near threshold excitation function for the pp-->ppK+K- reaction. As a result of these studies we have estimated the K+K- scattering length more precise compared to the previous analysis based only on the analysis of the differential cross sections.Comment: Proceedings from the MESON2010 conference ,3 pages, 3 figure

Full-Coupled Channel Approach to Doubly Strange ss-Shell Hypernuclei

We describe {\it ab initio} calculations of doubly strange, $S=-2$, $s$-shell hypernuclei ($^4_{\Lambda\Lambda}$H, $^5_{\Lambda\Lambda}$H, $^5_{\Lambda\Lambda}$He and $^6_{\Lambda\Lambda}$He) as a first attempt to explore the few-body problem of the {\it full}-coupled channel scheme for these systems. The wave function includes $\Lambda\Lambda$, $\Lambda\Sigma$, $N\Xi$ and $\Sigma\Sigma$ channels. Minnesota $NN$, D2$^\prime$ $YN$, and simulated $YY$ potentials based on the Nijmegen hard-core model, are used. Bound state solutions of these systems are obtained. We find that a set of phenomenological $B_8B_8$ interactions among the octet baryons in $S=0, -1$ and -2 sectors, which is consistent with all of the available experimental binding energies of $S=0, -1$ and -2 $s$-shell (hyper-)nuclei, can predict a particle stable bound state of $^4_{\Lambda\Lambda}$H. For $^5_{\Lambda\Lambda}$H and $^5_{\Lambda\Lambda}$He, $\Lambda N-\Sigma N$ and $\Xi N-\Lambda\Sigma$ potentials enhance the net $\Lambda\Lambda-N\Xi$ coupling, and a large $\Xi$ probability is obtained even for a weaker $\Lambda\Lambda-N\Xi$ potential.Comment: 4 pages, 1 figur

Structure of air shower disc near the core

The longitudinal structure of the air shower disk is studied by measuring the arrival time distributions of air shower particles for showers with electron size in the range 3.2 x 10 to the 5.5. power to 3.2 x 10 to the 7.5 power in the Akeno air-shower array (930 gcm squared atmospheric depth). The average FWHM as a parameter of thickness of air shower disk increases with core distances at less than 50m. AT the present stage, dependence on electron size, zenith angle and air shower age is not apparent. The average thickness of the air shower disk within a core distance of 50m could be determined by an electromagnetic cascade starting from the lower altitude

Superconductivity in Tetragonal LaPt_{2-x}Ge_{2+x}

We find that a tetragonal CaBe_2Ge_2-type structure can be stabilized in non-stoichiometric LaPt_{2-x}Ge_{2+x}. We further discovered that tetragonal LaPt_{2-x}Ge_{2+x} with x=0.15 and 0.2 respectively superconduct at Tc=1.85 K and 1.95 K, which is about four time higher than that in monoclinic LaPt_2Ge_2.Comment: 6 pages, 4 figure