Effect of n+-GaAs thickness and doping density on spin injection of GaMnAs/n+-GaAs Esaki tunnel junction

We investigated the influence of n+-GaAs thickness and doping density of GaMnAs/n+-GaAs Esaki tunnel junction on the efficiency of the electrical electron spin injection. We prepared seven samples of GaMnAs/n+-GaAs tunnel junctions with different n+-GaAs thickness and doping density grown on identical p-AlGaAs/p-GaAs/n-AlGaAs light emitting diode (LED) structures. Electroluminescence (EL) polarization of the surface emission was measured under the Faraday configuration with external magnetic field. All samples have the bias dependence of the EL polarization, and higher EL polarization is obtained in samples in which n+-GaAs is completely depleted at zero bias. The EL polarization is found to be sensitive to the bias condition for both the (Ga,Mn)As/n+-GaAs tunnel junction and the LED structure.Comment: 4pages, 4figures, 1table, To appear in Physica

Maximal rank of extremal marginal tracial states

States on coupled quantum system whose restrictions to each subsystems are normalized traces are called marginal tracial states. We investigate extremal marginal tracial states and maximal rank of such states. Diagonal marginal tracial states are also considered.Comment: 10 page

(In,Ga)As gated-vertical quantum dot with an Al2O3 insulator

We fabricated a gated-vertical (In,Ga)As quantum dot with an Al2O3 gate insulator deposited using atomic layer deposition and investigated its electrical transport properties at low temperatures. The gate voltage dependence of the dI/dV-V characteristics shows clear Coulomb diamonds at 1.1K. The metal-insulator gate structure allowed us to control the number of electrons in the quantum dot from 0 to a large number estimated to be about 130.Comment: 14 pages, 4 figures. Accepted to Applied Physics Letter

Nef vector bundles on a projective space with first Chern class 3 and second Chern class 8

We describe nef vector bundles on a projective space with first Chern class three and second Chern class eight over an algebraically closed field of characteristic zero by giving them a minimal resolution in terms of a full strong exceptional collection of line bundles.Comment: 10 pages. v.2: Corrected typos and an error in the proof. To appear in Le Matematich

Roles of citizens or "civil society" and responsibility of state

Civil Society became an important theme in the recent discussion of political or social theory. Civil Society is playing a substantial role for the legislation process. We can find it especially in the activities of international NGO. It gives a new aspect of the relationship between state and society, and legal philosophically speaking, of validity of law. Activities of Civil Society are socially recognized and their support systems are gradually institutionalized also domestic in Japan. But Japanese NPO has its own weak point, which arises from the political structure of our society