Nammee Kim

Characteristics of GaMnN based ferromagnetic resonant tunneling diode without external magnetic field

Achievement of a spin polarization without magnetic field through a GaMnN based ferromagnetic resonant tunneling diode (RTD) is proposed theoretically. The influences of the temperature and structure on the spin polarization current and differential conductance have been investigated. The clear spin splitting current can be observed in an optimal RTD structure without magnetic field even though the splitting energy of the ferromagnetic barrier is very small. Large spin polarization can be obtained and the polarization orientation can be varied by an applied bias voltage without external magnetic field.

Edge-channel transport through quantum wires with a magnetic quantum dot

We investigate the scattering of edge channels by a magnetic quantum dot, which is formed by two different magnetic fields B∗ and B0 inside and outside the dot, respectively, in a quantum wire. We calculate the two-terminal conductance (G) of the wire and find that for γ(=B∗/B0)>0, G is quantized, while for γ<0 it is not quantized. This feature results from the different magnetic confinements, caused by nonuniform magnetic fields, between the two cases.

Finite-temperature study of a modulation-doped DMS quantum well with broken spin symmetry

Abstract We present a finite-temperature self-consistent calculation of the electronic properties in a modulation doped dilute magnetic strucuture (DMS) QW structure with broken spin-symmetry. The spin-split subband structure is calculated at finite temperatures as a function of applied magnetic field. Temperature and magnetic field effects on the electronic properties are analyzed for various degrees of spin polarization. Carrier-induced magnetism and the possible ferromagnetic–paramagnetic phase transitions are analyzed in terms of various material parameters of the DMS QW structures.

Polarization switching effects in ferromagnetic/ferroelectric hybrid double quantum wells

The ferromagnetic transition temperature is investigated as a function of the electric field for a ferromagnetic/ferroelectric hybrid double quantum well (HDQW) system through the self‐consistent treatment of wave functions. These results are also compared with those obtained from the flat‐band model. We found that the self‐consistent treatment in obtaining ferromagnetic transition temperatures Tc/Tco is very important in the case of a high carrier density.

Effects of Magnetic Quantum Dots on Magnetoconductance in Quantum Wires

We present a theoretical study of electronic transport in quantum wires (narrow two-dimensional electron gas) with array of magnetic quantum dots. Each magnetic quantum dot is defined by a small circular region where the strength of perpendicular magnetic field is modulated. By making use of a newly developed calculation method based on the gauge transformations, we calculated the conductance as a function of the external perpendicular magnetic field. Our numerical calculations show that the magnetoconductance is very sensitive to the number of magnetic quantum dots in the field region where the direction of the net magnetic field in dot regions is antiparallel to the external magnetic field.

Dimensional crossover in cylindrical quantum-box structures formed by penetrable barriers

We study the density of states (DOS) in a cylindrical quantum box formed by a cylindrical penetrable barrier and a planer penetrable double barrier perpendicular to the cylinder. The control of the cylindrical barrier thickness or height is found to cause the dimensional transitions from a three-dimensional (3D) DOS to a quasi-one-dimensional (Q1D) DOS and from a quasi-two-dimensional (Q2D) DOS to a quasi-zero-dimensional (Q0D) DOS, if the strength of the planer double barrier is zero and infinity, respectively. In between the 3D and the Q1D (Q2D and Q0D) limiting regimes, we found the presence of a Q2D (Q1D) like crossover regime.