Dynamic nuclear polarization induced by hot electrons

A new method for local dynamic nuclear polarization is demonstrated in a GaAs/AlGaAs heterostructure at the Landau level filling factor $\nu=3$. Using a narrow channel sample, where the width varies stepwise along the electron flow, we find that electron cooling (heating) causes the polarization of nuclear spins against (toward) the external magnetic field at liquid helium temperatures. The longitudinal nuclear spin relaxation rate varies exponentially with inverse temperature.Comment: 3 pages, 3 figure

Magnetoresistance and spin polarization in the insulating regime of a Si two-dimensional electron system

We have studied the magnetoresistance in a high-mobility Si inversion layer down to low electron concentrations at which the longitudinal resistivity $\rho_{xx}$ has an activated temperature dependence. The angle of the magnetic field was controlled so as to study the orbital effect proportional to the perpendicular component $B_\perp$ for various total strengths $B_{\rm tot}$. A dip in $\rho_{xx}$, which corresponds to the Landau level filling factor of $\nu=4$, survives even for high resistivity of $\rho_{xx} \sim 10^8 \Omega$ at $T= 150 {\rm mK}$. The linear $B_{\rm tot}$-dependence of the value of $B_\perp$ at the dip for low $B_{\rm tot}$ indicates that a ferromagnetic instability does not occur even in the far insulating regime.Comment: 6 pages, 7 figures, submitted to PR

Quantum Hall effect at cleaved InSb surfaces and low-temperature annealing effect

We have performed low-temperature in-plane magnetotransport measurements on two-dimensional electron systems induced by deposition of Ag at {\it in situ} cleaved surfaces of {\it p}-type InSb. The quantum Hall effect was observed even at low magnetic fields around 2 T. The surface electron density and the electron mobility exhibit strong dependence on the Ag-coverage and the annealing temperature in the range of 15-40 K. The annealing effect suggests that the surface morphology strongly affects the properties of the two-dimensional electron systems.Comment: 3 pages, 2 figure

Evidence for Two-Dimensional Spin-Glass Ordering in Submonolayer Fe Films on Cleaved InAs Surfaces

Magnetotransport measurements have been performed on two-dimensional electron gases formed at InAs(110) surfaces covered with a submonolayer of Fe. Hysteresis in the magnetoresistance, a difference in remanent magnetoresistance between zero-field-cooling procedures and field-cooling procedures, and logarithmic time-dependent relaxation after magnetic field sweep are clearly observed at 1.7 K for a coverage of 0.42 monolayer. These features are associated with spin-glass ordering in the Fe film.Comment: 4 pages, 3 figure

Development of fully-automated synthesis systems

This paper describes the development of fully-automated synthesis systems for preparing and isolating various kinds of pharmaceutical compounds. The systems are versatile, and are able to perform most of the chemical reactions currently used in organic chemistry, with the exception of hydrogenation which requires high pressure. An additional benefit is the very user-friendly software