540 research outputs found
XOR logic gate on electron spin qubits in quadruple coupled quantum dots
The spin-dependent localization of electrons in quadruple quantum dots (QD's)
has been studied by the configuration interaction method. We have investigated
two nanodevices that consist of laterally coupled quadruple QD's. We have shown
that -- in both the nanodevices with suitably chosen parameters -- the
exclusive OR (XOR) logic gate can be realized by all-electrical control with
the readout of output via the spin-to-charge conversion. We have determined the
nanodevice parameters that are optimal for the performance of the XOR logic
gate.Comment: 4 pages, 5 figure
Spin filtering effect generated by the inter-subband spin-orbit coupling in the bilayer nanowire with the quantum point contact
The spin filtering effect in the bilayer nanowire with quantum point contact
is investigated theoretically. We demonstrate the new mechanism of the spin
filtering based on the lateral inter-subband spin-orbit coupling, which for the
bilayer nanowires has been reported to be strong. The proposed spin filtering
effect is explained as the joint effect of the Landau-Zener inter-subband
transitions caused by the hybridization of states with opposite spin (due to
the lateral Rashba SO interaction) and the confinement of carriers in the
quantum point contact region.Comment: 14 pages, 11 figure
Electrically controlled spin-transistor operation in helical magnetic field
A proposal of electrically controlled spin transistor in helical magnetic
field is presented. In the proposed device, the transistor action is driven by
the Landau-Zener transitions that lead to a backscattering of spin polarized
electrons and switching the transistor into the high-resistance state (off
state). The on/off state of the transistor can be controlled by the
all-electric means using Rashba spin-orbit coupling that can be tuned by the
voltages applied to the side electrodes.Comment: 5 pages, 6 figure
Lateral electron localization by the induced surface charge
We investigate the problem of the electron interacting with the charge
induced on the metal or dielectric surface. We show that the interaction
between the electron and the induced surface charge leads to the lateral
confinement of the electron. As a result the electron propagates parallel to
the surface not as a plane wave but as a wave packet of a Gaussian shape. The
electron moving together with the induced charge can be treated as a new
quasi-particle, which we call inducton. We discuss a possible experimental
evidence for inductons in semiconductor nanostructures, metal-vacuum, and
dielectric-vacuum interfaces.Comment: 4 pages, 4 figure
Non-ballistic spin separator based on Y-shaped nanostructure with a quantum point contact
A proposal of a spin separator based on the spin Zeeman effect in Y-shaped
nanostructure with a quantum point contact is presented. Our calculations show
that the appropriate tuning of the quantum point contact potential and the
external magnetic field leads to the spin separation of the current: electrons
with opposite spins flow through the different output branches. We demonstrate
that this effect is robust against the scattering on impurities. The proposed
device can also operate as a spin detector, in which -- depending on the
electron spin -- the current flows through one of the output branches.Comment: 5 pages, 4 figure
Spin filter effect at room temperature in GaN/GaMnN ferromagnetic resonant tunneling diode
We have investigated the spin current polarization without the external
magnetic field in the resonant tunneling diode with the emitter and quantum
well layers made from the ferromagnetic GaMnN. For this purpose we have applied
the self-consistent Wigner-Poisson method and studied the spin-polarizing
effect of the parallel and antiparallel alignment of the magnetization in the
ferromagnetic layers. The results of our calculations show that the
antiparallel magnetization is much more advantageous for the spin filter
operation and leads to the full spin current polarization at low temperatures
and 35 % spin polarization of the current at room temperature.Comment: 4 pages, 5 figure
Effect of current hysteresis on the spin polarization of current in a paramagnetic resonant tunneling diode
A spin-dependent quantum transport is investigated in a paramagnetic resonant
tunneling diode (RTD) based on a ZnMnSe/ZnBeSe heterostructure.
Using the Wigner-Poisson method and assuming the two-current model we have
calculated the current-voltage characteristics, potential energy profiles and
electron density distributions for spin-up and spin-down electron current in an
external magnetic field. We have found that -- for both the spin-polarized
currents -- two types of the current hysteresis appear on the current-voltage
characteristics. The current hysteresis of the first type occurs at the bias
voltage below the resonant current peak and results from the accumulation of
electrons in the quantum well layer. The current hysteresis of the second type
appears at the bias voltage above the resonant current peak and is caused by
the creation of the quasi-bound state in the left contact region and the
resonant tunneling through this quasi-bound state. The physical interpretation
of both the types of the current hysteresis is further supported by the
analysis of the calculated self-consistent potential profiles and electron
density distributions. Based on these results we have shown that -- in certain
bias voltage and magnetic field ranges -- the spin polarization of the current
exhibits the plateau behavior with the nearly full spin polarization. This
property is very promising for possible applications in spintronics.Comment: 11 pages, 10 figure
Spin transistor operation driven by the Rashba spin-orbit coupling in the gated nanowire
The theoretical description has been proposed for the operation of the spin
transistor in the gate-controlled InAs nanowire. The calculated current-voltage
characteristics show that the current flowing from the source (spin injector)
to the drain (spin detector) oscillates as a function of the gate voltage,
which results from the precession of the electron spin caused by the Rashba
spin-orbit interaction in the vicinity of the gate. We have studied two
operation modes of the spin transistor: (A) the ideal operation mode with the
full spin polarization of electrons in the contacts, the zero temperature, and
the single conduction channel corresponding to the lowest-energy subband of the
transverse motion and (B) the more realistic operation mode with the partial
spin polarization of the electrons in the contacts, the room temperature, and
the conduction via many transverse subbands taken into account. For mode (A)
the spin-polarized current can be switched on/off by the suitable tuning of the
gate voltage, for mode (B) the current also exhibits the pronounced
oscillations but with no-zero minimal values. The computational results
obtained for mode (B) have been compared with the recent experimental data and
a good agreement has been found.Comment: 8 pages, 11 figure
Periodicity of resonant tunneling current induced by the Stark resonances in semiconductor nanowire
The modification of the electronic current resulting from Stark resonances
has been studied for the semiconductor nanowire with the double-barrier
structure. Based on the calculated current-voltage characteristics we have
shown that the resonant tunneling current is a periodic function of the width
of the spacer layer. We have also demonstrated that the simultaneous change of
the source-drain voltage and the voltage applied to the gate located near the
nanowire leads to almost periodic changes of the resonant tunneling current as
a function of the source-drain and gate voltages. The periodic properties of
the resonant tunneling current result from the formation of the Stark resonance
states. If we change the electric field acting in the nanowire, the Stark
states periodically acquire the energies from the transport window and enhance
the tunneling current in a periodic manner. We have found that the separations
between the resonant current peaks on the source-drain voltage scale can be
described by a slowly increasing linear function of the Stark state quantum
number. This allows us to identify the quantum states that are responsible for
the enhancement of the resonant tunneling. We have proposed a method of the
experimental observation of the Stark resonances in semiconductor
double-barrier heterostructures.Comment: 9 pages, 8 figure
Intrinsic oscillations of spin current polarization in a paramagnetic resonant tunneling diode
A spin- and time-dependent electron transport has been studied in a
paramagnetic resonant tunneling diode using the self-consistent Wigner-Poisson
method. Based on the calculated current-voltage characteristics in an external
magnetic field we have demonstrated that under a constant bias both the spin-up
and spin-down current components exhibit the THz oscillations in two different
bias voltage regimes. We have shown that the oscillations of the spin-up (down)
polarized current result from the coupling between the two resonance states:
one localized in the triangular quantum well created in the emitter region and
the second localized in the main quantum well. We have also elaborated the
one-electron model of the current oscillations, which confirms the results
obtained with the Wigner-Poisson method. The spin current oscillations can
lower the effectiveness of spin filters based on the paramagnetic resonant
tunneling structures and can be used to design the generators of the spin
polarized current THz oscillations that can operate under the steady bias and
constant magnetic field.Comment: 11 pages, 8 figures, to be published in Phys.Rev.
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