Theory of huge tunneling magnetoresistance in graphene

We investigate theoretically the spin-independent tunneling magnetoresistance effect in a graphene monolayer modulated by two parallel ferromagnets deposited on a dielectric layer. For the parallel magnetization configuration, Klein tunneling can be observed in the transmission spectrum but at specific oblique incident angles. For the antiparallel magnetization configuration, the transmission can be blocked by the magneticelectric barrier provided by the ferromagnets. Such a transmission discrepancy results in a tremendous magnetoresistance ratio and can be tuned by the inclusion of an electric barrier.

Single-electron tunneling depressing synapse for cellular neural networks

In this paper, a cellular neural network with depressing synapses for contrast-invariant pattern classification and synchrony detection is presented, starting from the impulse model of the single-electron tunneling junction. The results of the impulse model and the network are simulated using simulation program with integrated circuit emphasis (SPICE). It is demonstrated that depressing synapses should be an important candidate of robust systems since they exhibit a rapid depression of excitatory postsynaptic potentials for successive presynaptic spikes.

Resonant tunneling through S- and U-shaped graphene nanoribbons

We theoretically investigate resonant tunneling through S- and U-shaped nanostructured graphene nanoribbons. A rich structure of resonant tunneling peaks is found emanating from different quasi-bound states in the middle region. The tunneling current can be turned on and off by varying the Fermi energy. Tunability of resonant tunneling is realized by changing the width of the left and/or right leads and without the use of any external gates.

Tunneling magnetoresistance in (Ga,Mn)As/Al-O/CoFeB hybrid structures

Tunneling magnetoresistance (TMR) in Ga(0.9)2Mn(0.08)As/Al-O/Co40Fe40B20 trilayer hybrid structure as a function of temperature from 10 to 50 K with magnetic field vertical bar H vertical bar <= 2000 Oe has been studied. TMR ratio of 1.6% at low fields at 10 K was achieved with the applied current of 1 mu A. The behavior of junction resistance was well explained by the tunneling resistance across the barrier. Strong bias dependences of magnetoresistance and junction resistance were presented. (C) 2009 American Institute of Physics. [DOI 10.1063/1.3068418]

Experimental verification on the origin of plateau-like current-voltage characteristics of resonant tunneling diodes

Current-voltage (I-V) characteristics of GaAs-based resonant tunneling diodes have been investigated in the presence of a perpendicular magnetic field. Electron resonant tunneling is strongly suppressed by the applied magnetic field, leading to peak current decreasing with increasing magnetic field. The observed plateau-like structures appear in negative differential resistance region on the I-V curves and are magnetic-field dependent. The plateau-like structures are due to the coupling between the energy levels in the emitter well and in the main quantum well. (C) 2004 American Institute of Physics.

Spin-dependent tunneling through a symmetric semiconductor barrier: The Dresselhaus effect

Spin-dependent tunneling through a symmetric semiconductor barrier is studied including the k(3) Dresselhaus effect. The spin-dependent transmission of an electron can be obtained analytically. By comparing with previous work [Phys. Rev. B 67, 201304(R) (2003) and Phys. Rev. Lett. 93, 056601 (2004)], it is shown that the spin polarization and interface current are changed significantly by including the off-diagonal elements in the current operator, and can be enhanced considerably by the Dresselhaus effect in the contact regions.

The quantum tunneling between two-component Bose-Einstein condensates in a double-well configuration

In terms of exact solution of the time-dependent Schrodinger equation. we examine the quantum tunneling process in Bose condensates of two interacting species trapped in a double well configuration. We use the two series of time-dependent SU(2) gauge transformation to diagonalize the Hamilton operator obtain analytic time-evolution formulas of the population imbalance and the berry phase. The particle population imbalance (a(L)(+)a(L) - a(R)(+)a(R)) of species A between the two wells is studied analytically.

Photoinduced voltage shift in a three-barrier, two-well resonant tunneling structure integrated with a 1.2-mu m-thick n-type GaAs layer

By integrating a three-barrier, two-well resonant tunneling structure with a 1.2-mu m-thick, slightly doped n-GaAs layer, a photoinduced voltage shift on the order of magnitude of 100 mV in resonant current peaks has been verified at an irradiance of low light power density. The 1.2-mu m-thick, slightly doped n-GaAs layer manifests itself of playing an important role in enhancing photoelectric sensitivity. (c) 2005 Elsevier B.V. All rights reserved.

Spin-polarized tunneling through a diluted magnetic semiconductor quantum dot

Spin-polarized tunneling through a diluted magnetic semiconductor quantum dot embedded in a tunneling barrier is investigated using the Bardeen transfer Hamiltonian. The tunneling current oscillates with an increasing magnetic field for a fixed bias. Many peaks are observed with an increasing external bias under a fixed magnetic field. Spin polarization of the tunneling current is tuned by changing the external bias under a weak magnetic field.

Dynamics of spin-dependent tunneling through a semiconductor double-barrier structure

The dynamics of spin-dependent tunneling through a nonmagnetic semiconductor double-barrier structure is studied including the k(3) Dresselhaus spin orbit coupling is solved by the time-dependent Schrodinger equation with a developed method for the finite-difference relaxation. The resonant peak and quasibound level lifetime are determined by the in-plane wave vector and the applied electric field. The buildup time and decay lifetime of resonant probability amplitude are different for the spin-down and spin-up electrons due to the Dresselhaus spin-orbit coupling. Further investigation shows that the steady spin-polarization in both the well and collector regions has been obtained in the time domain. (C) 2007 American Institute of Physics.

Greatly enhanced resonant tunneling of photo-excited holes in a three-barrier resonant tunneling structure

By integrating a resonant tunneling diode with a 1.2 mu m-thick slightly doped n-type GaAs layer in a three-barrier, two-well resonant tunneling structure, the resonant tunneling of photo-excited holes exhibits a value of peak-to-valley current ratio (PVCR) as high as 36. A vast number of photo-excited holes generated in this 1.2 mu m-thick slightly doped n-type GaAs layer, and the quantization of hole levels in a 23nm-thick quantum well on the outgoing side of hole tunneling out off the resonant tunneling diode which greatly depressed the valley current of the holes, are thought to be responsible for such greatly enhanced PVCR.

Effects of phase-breaking on long-range charge transfer in DNA: Partially-coherent-tunneling model study

The mechanism of hole charge transfer in DNA of various lengths and sequences is investigated based on a partially coherent tunneling theory (Zhang et al., J Chem Phys 117:4578, 2002), where the effects of phase-breaking in adenine-thymine and guanine-cytosine base pairs are treated on equal foot. This work aims at providing a self-consistent microscopic interpretation for rate experiments on various DNA systems. We will also clarify the condition under which the simple superexchange-mediated-hopping picture is valid, and make some comments on the further development of present theory.

Electron resonant tunneling through InAs/GaAs quantum dots embedded in a Schottky diode with an AlAs insertion layer

Molecular beam epitaxy was employed to manufacture self-assembled InAs/GaAs quantum dot Schottky resonant tunneling diodes. By virtue of a thin AlAs insertion barrier, the thermal current was effectively reduced and electron resonant tunneling through quantum dots under both forward and reverse biased conditions was observed at relatively high temperature of 77 K. The ground states of quantum dots were found to be at similar to 0.19 eV below the conduction band of GaAs matrix. The theoretical computations were in conformity with experimental data. (c) 2006 The Electrochemical Society.

New type of Fano resonant tunneling via Anderson impurities in superlattice

The spectrum of differential tunneling conductance in Si-doped GaAs/AlAs superlattice is measured at low electric fields. The conductance spectra feature a zero-bias peak and a low-bias dip at low temperatures. By taking into account the quantum interference between tunneling paths via superlattice miniband and via Coulomb blockade levels of impurities, we theoretically show that such a peak-dip structure is attributed to a Fano resonance where the peak always appears at the zero bias and the line shape is essentially described by a new function \xi\/\xi\+1 with the asymmetry parameter q approximate to 0. As the temperature increases, the peak-dip structure fades out due to thermal fluctuations. Good agreement between experiment and theory enables us to distinguish the zero-bias resonance from the usual Kondo resonance.

Room-temperature observation of electron resonant tunneling through InAs/AlAs quantum dots

Molecular beam epitaxy is employed to manufacture self-assembled InAs/AlAs quantum-dot resonant tunneling diodes. The resonant tunneling current is superimposed on the thermal current, and together they make up the total electron transport in devices. Steps in current-voltage characteristics and peaks in capacitance-voltage characteristics are explained as electron resonant tunneling via quantum dots at 77 or 300 K, and thus resonant tunneling is observed at room temperature in III-V quantum-dot materials. Hysteresis loops in the curves are attributed to hot electron injection/emission process of quantum dots, which indicates the concomitant charging/discharging effect. (c) 2006 The Electrochemical Society.