Asymmetric Confinement Potential Research Articles

Reversible and Nonvolatile Manipulation of the Spin-Orbit Interaction in Ferroelectric Field-Effect Transistors Based on a Two-Dimensional Bismuth Oxychalcogenide

The spin-orbit interaction (SOI) offers a nonferromagnetic scheme to realize spin polarization through utilizing an electric field. Electrically tunable SOIs through electrostatic gates have been investigated; however, the relatively weak and volatile tunability limits their practical applications in spintronics. Here, we demonstrate the nonvolatile electric field control of the SOI via constructing ferroelectric Rashba architectures, i.e., two-dimensional ${\mathrm{Bi}}_{2}{\mathrm{O}}_{2}\mathrm{Se}/\mathrm{Pb}({\mathrm{Mg}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_{3}$-${\mathrm{PbTiO}}_{3}$ ferroelectric field-effect transistors. The experimentally observed weak antilocalization (WAL) cusp in ${\mathrm{Bi}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ films implies the Rashba-type SOI that arises from the asymmetric confinement potential. Significantly, taking advantage of the switchable ferroelectric polarization, the WAL-to-weak-localization-transition trend reveals the competition between spin relaxation and the dephasing process, and the variation of carrier density leads to a reversible and nonvolatile modulation of the spin-relaxation time and the spin-splitting energy of ${\mathrm{Bi}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ films by this ferroelectric gating. Our work provides a scheme to achieve nonvolatile control of the Rashba SOI with the utilization of ferroelectric remanent polarization.

Temperature effect of strong-coupling polaron in RbCl quantum wells with double asymmetric confined potentials

In this study, the ground state properties of strong-coupling polaron in RbCl quantum wells (QWs) by using double asymmetric confined potential were theoretically investigated based on effective mass approximation. Ground state binding energy (GSBE), ground state energy (GSE), vibrational frequency (VF), and mean LO phonon number (MLOPN) were obtained as functions of asymmetric confinement potential parameters in QWs by using the unitary transformation method and linear combination operator. GSBE, GSE, VF and MLOPN were found to be increasing functions of asymmetric semi-exponential confinement potential (ASECP) parameter [Formula: see text] and decreasing functions of parameter [Formula: see text]. GSE was rapidly increased with the increase of confinement strength. GSBE, GSE, VF and MLOPN increase as the increasing (decreasing) of anisotropic parabolic confinement potential strength (confinement length). In addition, the temperature effect was evaluated by using quantum statistical theory. With the increase of temperature, GSE and GSBE decreased while VF and MNLOP increased.

Engineering electron wavefunctions in asymmetrically confined quasi one-dimensional structures

We present results on electron transport in quasi-one dimensional quantum wires in GaAs/AlGaAs heterostructures obtained using an asymmetric confinement potential. The variation of the energy levels of the spatially quantized states is followed from strong confinement through weak confinement to the onset of two dimensionality. An anticrossing of the initial ground and first excited states is found as the asymmetry of the potential is varied, giving rise to two anticrossing events, which occur on either side of symmetric confinement. We present results analyzing this behavior and showing how it can be affected by the inhomogeneity in background potential. The use of an enhanced source-drain voltage to alter the energy levels is shown to be a significant validation of the analysis by showing the formation of double rows of electrons, which correlate with the anticrossing.

Formation of a non-magnetic, odd-denominator fractional quantized conductance in a quasi-one-dimensional electron system

We have investigated the transport properties of a two-dimensional electron gas confined to one dimension by voltages applied to a pair of split gates and an additional top gate deposited on the surface of the GaAs/AlGaAs heterostructure. At low carrier concentrations, <5 × 1010 cm−2, in a wide 1D channel (700 nm), with an asymmetric confinement potential, the conductance plateaux in units of e2/h at 1 and 2/3 were observed. In the presence of a fixed in-plane magnetic field of 10 T, additional plateaux at 2/5 and 2/7 appeared with increasing asymmetry in confinement potential. The appearance of odd-denominator fractional states seems to originate from the zigzag formed when electrons are allowed to relax in the second dimension at the boundary of the 1D-2D transition.

Dust Particle Pair Correlation Functions and the Nonlinear Effect of Interaction Potentials

Dust kinetic temperature is a measure of the energy of the stochastic motion of a dust particle and is a result of the combination of the Brownian motion and the fluctuations in the dust charge and confining electric field. A method using the equilibrium value of the mean square displacement was recently introduced to obtain the dust kinetic temperature experimentally. As a follow up, this paper investigates the relationship between the dust kinetic energy derived from the mean square displacement technique and a technique using the probability distribution of the displacements obtained from random fluctuations of the dust particle. The experimental results indicate that the harmonic confinement potential acting on the dust particle can be obtained by combining the two methods, allowing the nonlinear effect of the confining force to be investigated. The thermal expansion in a 1-D vertical chain is discussed as a representative application as it is related to the nonlinear confinement force, or the asymmetric confinement potential.

Excitonic properties in an asymmetric quantum dot nanostructure under combined influence of temperature and lateral hydrostatic pressure

Abstract Simultaneous influences of temperature and lateral hydrostatic pressure combined to axial asymmetric confinement potential and size effects on the behavior of the exciton in 0D GaAs / Ga ( 1 - x j ) A l ( x j ) asymmetric cylindrical quantum dot (QD) nanostructure are investigated. Our calculations are performed in the framework of the effective mass approximation by using a variational method with a robust trial wave function through taking into account the dependence of exciton properties on the QD sizes, the axial asymmetric confinement potential, the temperature and the pressure. Variation of the excitonic binding energy, photoluminescence energy transition and band gap energy are discussed according to temperature and hydrostatic pressure for different confinement regimes and various potential wells. Our numerical findings show that the applied pressure favors the attraction between electron and hole while the temperature tends to decrease the exciton binding energy. Furthermore, the photoluminescence energy is decreasing function of the temperature and increasing function of the pressure. The opposing influences caused by temperature and lateral hydrostatic pressure with contribution of variation of axial asymmetric confinement potential reveal a significant practical interest and offer an alternative manner to the tuning of the excitonic transition in optoelectronic devices.

Strong and Tunable Spin-Orbit Coupling in a Two-Dimensional Hole Gas in Ionic-Liquid Gated Diamond Devices.

Hydrogen-terminated diamond possesses due to transfer doping a quasi-two-dimensional (2D) hole accumulation layer at the surface with a strong, Rashba-type spin-orbit coupling that arises from the highly asymmetric confinement potential. By modulating the hole concentration and thus the potential using an electrostatic gate with an ionic-liquid dielectric architecture the spin-orbit splitting can be tuned from 4.6-24.5 meV with a concurrent spin relaxation length of 33-16 nm and hole sheet densities of up to 7.23 × 10(13) cm(-2). This demonstrates a spin-orbit interaction of unprecedented strength and tunability for a 2D hole system at the surface of a wide band gap semiconductor. With a spin relaxation length that is experimentally accessible using existing nanofabrication techniques, this result suggests that hydrogen-terminated diamond has great potential for the study and application of spin transport phenomena.

Spin polarization of the asymmetric quantum point contact and conductance anomalies in the case of resonances

We study spin polarization and conductance of the asymmetric quantum point contact. We consider both Rashba coupling and lateral spin–orbit interaction induced by laterally asymmetric confinement potential. We show that in longitudinally symmetric quantum point contact, the spin polarization is not accompanied by the appearance of the conductance plateau at 0.5G0(G0=2e2/h). In longitudinally asymmetric quantum point contact the above plateau arises due to the presence of resonant states within the using one-electron approximation. An explanation of the experimental fact that the plateau exists only for a limited range of variation of the gate voltage is given.

Morphology-Driven Stark Shift Switching in Ge/Si Type-II Heterointerfaces

Morphology-related anomaly was found in the photoluminescence (PL) of Ge/Si type-II double heterostructures with varying Ge coverage. PL Stokes shifts of 2-D Ge wetting layers functioning as a quantum well for holes switched from negative to positive under electric field as Ge coverage crossed 3.7 monolayers, which correlates well with the onset of Stranski-Krastanow growth mode transition. The origin of such shift polarity switch is discussed in terms of the linear Stark effect in an asymmetric confinement potential developing due to 3-D Ge islands.

Anomalous conductance quantization observed in a quantum point contact with an asymmetric confinement potential

The conductance through a quantum point contact with an asymmetric confinement potential has been studied. Multiple anomalous conductance plateaus were observed, around 0.5G0 and 0.9G0, when the confinement potential of the QPC was set to be asymmetric. Also, resonance-like conductance peaks were observed in some devices for highly asymmetric confinement potentials while some of the peaks evolved into anomalous conductance plateaus when the asymmetry was reduced. We found that the spin polarization model based on spin-orbit coupling in an asymmetric confinement potential could not directly explain our data.

Contactless electroreflectance of optical transitions in tunnel-injection structures composed of an In0.53Ga0.47As/In0.53Ga0.23Al0.24As quantum well and InAs quantum dashes

Tunnel-injection structures composed of an In0.53Ga0.47As/In0.53Ga0.23Al0.24As quantum well (QW) and a layer of InAs quantum dashes (QDashes) separated by In0.53Ga0.23Al0.24As barriers of various thicknesses have been investigated by contactless electroreflectance. The observed spectral features have been explained taking into account the optical transitions in a combined system of In0.53Ga0.47As QW and InAs QDash wetting layer. It has been shown that there exist electron and hole states which are localized on both sides of such an asymmetric confinement potential. The latter has allowed concluding that the QDash region in tunnel-injection structures can be easily penetrated by the carriers due to the presence of the wetting layer in the self-assembled structure.

A three-terminal spin filter induced by spin-orbit interaction in the presence of an antidot

The generation of a spin-polarized electric current is one of the key issues in the field of semiconductor spintronics. We show by numerical simulation that a three-terminal conductor with an antidot potential at the junction can be used as a spin filter. In addition, one can control the direction of spin polarization by changing the Fermi energy with respect to the height of antidot potential. This is understood by the interplay between spin-orbit coupling and the curvature of the potential. We also investigate the effect of disorder and an asymmetric confinement potential in order to clarify the validity of the spin filter.

Diffuse transport and spin accumulation in a Rashba two-dimensional electron gas

The Rashba Hamiltonian describes the splitting of the conduction band as a result of spin-orbit coupling in the presence of an asymmetric confinement potential and is commonly used to model the electronic structure of confined narrow-gap semiconductors. Due to the mixing of spin states some care has to be exercised in the calculation of transport properties. We derive the diffusive conductance tensor for a disordered two-dimensional electron gas with spin-orbit interaction and show that the applied bias induces a spin accumulation, but that the electric current is not spin-polarized.

Improved luminescence quality with an asymmetric confinement potential in Si-based type-II quantum wells grown on a graded SiGe relaxed buffer

A new class of Si-based quantum confined geometry is demonstrated using a combination of oppositely strained layers grown on a step-graded relaxed SiGe buffer. The role of heterointerfaces is revealed as the controlling mechanism of the exciton localization, which results in enhanced no-phonon transition intensity.

High mobility 2-D hole gases in strained Ge channels on Si substrates studied by magnetotransport and cyclotron resonance

High mobility two-dimensional hole gases have been achieved in p-type modulation doped Ge/SiGe heterostructures grown by MBE on a relaxed graded SiGe buffer. Hall mobilities of up to 15,500 cm 2/Vs at carrier densities of 1.04 × 10 12cm −2 are observed at 0.4 K in magnetotransport. The cyclotron resonance (CR) shows a narrow (FWHM 15 cm −1) and strong absorption of up to 15%. Quantum transitions are resolved. A splitting of the CR is observed, attributed to the lifting of the spin degeneracy of the ±3/2 states at B = 0 due to the asymmetric confinement potential. Mean CR masses of 0.14 m 0 up to 0.20 m 0 are found depending on well width and carrier density.