Shinji Nonoyama

Spin-dependent transport in a double barrier structure with a ferromagnetic material emitter

Abstract The differential conductance for a double barrier resonant tunnel diode is calculated by a recursive Green-function method based on the Keldysh formalism. The calculated results show that the conductance is strongly spin dependent for only the case where a positive bias voltage is applied between two barriers. The life time broadening at the Fermi level due to the magnetic impurity is found to be important to understand the dip structure of the conductance curve in experimental results. The features of the splitting of the dips in the calculated results are consistent with those in the experimental results.

Influence of disorder on the perpendicular magnetoresistance of magnetic multilayers

The e!ect of disorder on the perpendicular magnetoresistance of magnetic multilayers is investigated theoretically. Various kinds of disorder are considered: (i) interface substitutional disorder and (ii) bulk disorder in the various layers and in the leads. The calculations are based upon the non-equilibrium Green’s function formalism, together with the recursion method for calculating the real-space Green’s function. ( 1999 Elsevier Science B.V. All rights reserved.

Spin excitations of a ferromagnetic wire with a magnetic domain wall

Abstract The spin excitation for a ferromagnetic wire with a domain wall (DW) is studied in a framework of the random phase approximation. We show that the excitation energy due to the DW is much smaller than that for the spin wave. In the spin-wave spectrum, there are lots of peaks or shoulders, which is related to the existence of the DW and the dimension of the leads. Using the results, the energy dissipation of conduction electrons is also discussed.

Ab Initio Cluster Study of the Interaction of Hydrogen with the GaAs(100) Surface

The GaAs(100) surface is modeled, using a cluster to study the interaction with hydrogen. On the basis of ab initio theory including electron correlations, the most stable structures for the As-terminated surface with adsorbed hydrogen atoms are established. The optimized structure of the modeled cluster without the adsorbate is also obtained. From the computational results of total energy, the activation energy of the dissociation of the hydrogen molecule on the surface was estimated. The cluster with adsorbed hydrogen atoms is more stable than that without hydrogen, although the approach of the hydrogen molecule toward the surface causes an increase in the total energy.

Numerical studies of quantum conduction through a junction of wide‐narrow geometry

The conductance of the wide‐narrow geometry in the ballistic transport regime has been calculated by numerical scattering matrix methods. The oscillations of the conductance as a function of the width of the wide region relative to that of the narrow region was found. The period of oscillation corresponds to twice the width, where a new subband is generated as the width of the wide region is increased. The amplitude of the oscillation decreases with an increase in the width of the wide region. The effects of contact potential at a junction are also discussed.

QUANTUM INTERFERENCE EFFECTS OF ELECTRONS SCATTERED BY ANTIDOTS IN MAGNETIC FIELDS

Abstract We investigate the quantum transport phenomena for a quasi-one-dimensional quantum wire with antidots in magnetic fields. The calculated magnetoconductance shows a quasi-periodic structure of the group of dips. The characteristic properties of the magnetoconductance can be understood through a simple hopping model, where the electron transfers between the neighboring pinned orbits. We also discuss the interference effects on the conductance in connection with local electronic states.

Study of the Effect of Coulomb Repulsion on Resonant Tunneling in Magnetic Fields

The effect of on-site Coulomb repulsion on the process of resonant tunneling through a small interacting region is studied in the presence of a magnetic field by using the recursive Greens function method within a mean field approximation. The conductance is calculated as a function of the chemical potential µ making use of the Kubo formula, and calculations are performed for single- and double-mode quasi-one-dimensional quantum wires. In a magnetic field, some resonance levels close each other to form a single Landau level, so that the electron correlation in the small region is enhanced, and the µ-dependence of the conductance is changed by rather small value of the Coulomb repulsion. For the double-mode wire a collinear-type electronic state, in which spins in the small region are aligned antiferromagnetically in the x -direction and ferromagnetically in the y -direction, is found to be stable over a wide range of the chemical potential.

ELECTRON SCATTERING BY A RING-SHAPED BARRIER IN MAGNETIC FIELDS

Abstract We investigate the transport phenomena through a region containing a ring-shaped barrier in a quasi-one-dimensional quantum wire in magnetic fields. The calculated magnetoconductance curve shows a periodic dip structure, which is superimposed upon by another quasi-periodic dip structure. The current distributions for resonant states and the magnetoconductance features are well explained on the basis of the magnetic field dependence of the eigenvalue in the two-dimensional system.

Resonant Reflections in a Particle Conducting Through a Normal-Conductor–Superconductor Interface in Magnetic Fields

A quantum resonance in the conduction through the normal-conductor–superconductor junction is investigated in the presence of a magnetic field using a numerical transfer matrix method. It is shown that dip-pairs in the conductance curve occur at a certain geometry of the system owing to the resonant reflection caused by the interference of the reflected electron and hole waves under a finite magnetic field. By examining a local density of quasiparticles, we found that the feature of the resonant state giving the dip-pair in the conductance (in a magnetic field) is very different from that in a finite bias voltage.

Direct calculation of nonequilibrium current in a magnetic field

Abstract We calculate nonlinear I–V characteristics in the system comprising a tunnel junction and a rectangle barrier to study quantum interference effects using the lattice Greens function method based on Keldyshs theory.