Double-barrier Potential Research Articles

Transmission in graphene through time periodic double barrier potential

Transmission of Dirac fermions through a chip of graphene under the effect of a magnetic field and a time oscillating double barrier with frequency ω is investigated. Quantum interference within the oscillating barrier has an important effect on quasi-particle tunneling. The combination of both time dependent potential and magnetic field generates physical states whose energy is double quantized as reflected by the integer pair quantum numbers with a high degeneracy. The large number of modes that exist in the energy spectrum presents a colossal difficulty in the evaluation of physical results for arbitrary parameters. Thus we restricted our computations to weak time dependent perturbations so that we could limit ourselves to the central and two adjacent sidebands ().

Band tunneling through double barrier in biased graphene bilayer

We calculate the transport properties of charge carriers in graphene bilayers across symmetric and asymmetric double potential barrier considering energies exceeding the inter-layer coupling where two transport modes exist. Evaluating the transmission and reflection probabilities and corresponding conductances, we show that the transport is sensitive to the distance between the two barriers. Moreover, we explain the characteristic features observed in the numerical calculations, such as resonance tunneling at normal incidence, based on the Febry–Pèrot oscillations and ballistic transmission carried out by the evanescent waves. Finally, we compute the conductance of each mode separately and investigate contributions from inter-mode scattering and show that some geometric potential parameters can be used to control the total conductance of the system.

Dark soliton scattering in symmetric and asymmetric double potential barriers

Dark soliton scattering in symmetric and asymmetric double potential barriers

Controllable Goos-Hänchen shift in graphene triangular double barrier

We study the Goos-Hänchen (GH) shifts for Dirac fermions in graphene scattered by a triangular double barrier potential. The massless Dirac-like equation was used to describe the scattered fermions by such potential configuration. Our results show that the GH shifts is affected by the geometrical structure of the double barrier. In particular the GH shifts change sign at the transmission zero energies and exhibit enhanced peaks at each bound state associated with the double barrier when the incident angle is less than the critical angle associated with total reflection.

Tamm states in graphene-based different combined magneto-electric superlattice heterostructures

Tamm states localized at the interface between a homogeneous potential barrier and a combined magneto-electric potential barriers superlattice in monolayer graphene have been theoretically investigated. The results show that the symmetries of Tamm states are different when the components of the superlattice are different. When the single unit of the superlattice consists of double anti-parallel potential barriers and two gaps, Tamm states present symmetry about momentum wave vector ky′=0 at the same intensity of the homogeneous potential barrier (Vs). When the single unit of the superlattice consists of double anti-parallel magnetic potential barriers and two gaps, it demonstrates that Tamm states at positive Vs are symmetric to that at negative Vs about the electron incident energy E0=0. When the single unit of the superlattice consists of double anti-parallel combined magneto-electric potential barriers, the band gap at Dirac point is opened, Tamm states exhibit no symmetry about ky′ or the electron incident energy whether at the same Vs or at positive and negative Vs.

Quantum noise with exchange and tunnelling: predictions for a two-particle scattering experiment with time-dependent oscillatory potentials

.Quantum noise with exchange and tunnelling is studied within time-dependent wave packets. A novel expression for the quantum noise of two identical particles injected simultaneously from opposite sides of a tunnelling barrier is presented. Such quantum noise expression provides a physical (non-spurious) explanation for the experimental detection of two electrons at the same side under static potentials. Numerical simulations of the two-particle scattering probabilities in a double barrier potential with an oscillatory well are performed. The dependence of the quantum noise on the electron energy and oscillatory frequency is analysed. The peculiar behaviour of the dependence of the quantum noise on such parameters is proposed as a test about the soundness of this novel quantum noise expression, for either static or oscillatory potentials.

Glancing angle deposited WO3 nanostructures for enhanced sensitivity and selectivity to NO2 in gas mixture

We report the facile synthesis and the chemoresistive performances of villi-like WO3 nanostructures (VLWNs) which were fabricated by RF sputter with glancing angle deposition (GAD) mode. A fast deposition of GAD effectively forms self-assembled anisotropic nanostructures with high porosity and surface-to-volume ratio. The sensing tests were examined for NO2 detection in dry air and a mixture of reducing gases. As a result, these sensors at 200°C exhibit an highly selective and sensitive NO2 detection down to 800 parts per trillion (ppt) level, and could also respond well to NO2 in the concentration range of 0.2–1 parts per million (ppm) without the interference of gas mixture. These results show that the enhanced sensing properties to NO2 are attributed to the highly efficient surface modulation by double potential barriers at nano-necks of WO3 nanostructures.

Voltage tunable dielectric properties of oxides at nanoscale: TiO2 and CeO2 as model systems

Carrier transport through electrically active grain boundaries has been studied under biased condition using Solartron 1260 impedance/gain phase analyzer with an applied AC potential of 250 mV in the frequency range 1 Hz–1 MHz for nanocrystalline TiO2 and CeO2 as the model systems. Prior to the measurement both the materials were converted into cylindrical pellets with (8 mm diameter and 1 mm thick) by applying uni-axial pressure of 4 ton using a hydraulic press, then sintered at 300, 450 and 600 °C for 30 min for TiO2 sample and for the case of CeO2 it was done at 300, 600 and 900 °C for 30 min. Further, they were characterized using powder X-ray diffractometer (XRD) and transmission electron microscopy (TEM) to know the crystal structure, average crystallite size and morphology. The impedance measurements were performed at room temperature under applied DC bias voltages from 0 to 3 V in the periodic increment of 0.2 V. The observed applied bias voltage effect on dielectric constant of both the systems was analyzed with ‘grain boundary double Schottky potential barrier height model’ for different grain sizes. The percentage of voltage tunable dielectric constant (T%) as a function of frequency was estimated for all the grain sizes and it was found to be increase with reduction of grain size. Our experimental findings reveal the possibilities of utilizing these nanocrystals as a potential active material for phased array antenna since both the samples exhibits T% = 85% at 100 Hz frequency.

Transmission and Goos-Hänchen like shifts through a graphene double barrier in an inhomogeneous magnetic field

We studied the transport properties of electrons in graphene as they are scattered by a double barrier potential in the presence of an inhomogeneous magnetic field. We computed the transmission coefficient and Goos-H\"anchen like shifts for our system and noticed that transmission is not allowed for certain range of energies. In particular, we found that, in contrast to the electrostatic barriers, the magnetic barriers are able to confine Dirac fermions. We also established some correlation between the electronic transmission properties of Dirac fermions with the Goos-H\"anchen like shifts, as reflected in the numerical data.

On the generalized Hartman effect for symmetric double-barrier point potentials

We consider the scattering of a non-relativistic particle by a symmetrical arrangement of two identical barriers in one-dimension, with the barriers given by the well-known four-parameter family of point interactions. We calculate the phase time and the stationary Salecker-Wigner-Peres clock time for the particular cases of a double δ and a double δ' barrier and investigate the off-resonance behavior of these time scales in the limit of opaque barriers, addressing the question of emergence of the generalized Hartman effect.

Electronic properties of core-shell nanowire resonant tunneling diodes.

The electronic sub-band structure of InAs/InP/InAs/InP/InAs core-shell nanowire resonant tunneling diodes has been investigated in the effective mass approximation by varying the core radius and the thickness of the InP barriers and InAs shells. A top-hat, double-barrier potential profile and optimal energy configuration are obtained for core radii and surface shells >10 nm, InAs middle shells <10 nm, and 5 nm InP barriers. In this case, two sub-bands exist above the Fermi level in the InAs middle shell which belongs to the m = 0 and m = 1 ladder of states that have similar wave functions and energies. On the other hand, the lowest m = 0 sub-band in the core falls below the Fermi level but the m = 1 states do not contribute to the current transport since they reside energetically well above the Fermi level. We compare the case of GaAs/AlGaAs/GaAs/AlGaAs/GaAs which may conduct current with smaller applied voltages due to the larger effective mass of electrons in GaAs and discuss the need for doping.

Reduction of local velocity spreads by linear potentials

We study the spreading of the wave function of a Bose-Einstein condensate accelerated by a constant force both in the absence and in the presence of atom-atom interactions. We show that, despite the initial velocity dispersion, the local velocity dispersion defined at a given position downward can reach ultralow values and be used to probe very narrow energetic structures. We explain how one can define quantum mechanically and without ambiguities the different velocity moments at a given position by extension of their classical counterparts. We provide a common theoretical framework for interacting and non-interacting regimes based on the Wigner transform of the initial wave function that encapsulates the dynamics in a scaling parameter. In the absence of interaction, our approach is exact. Using a numerical simulation of the 1D Gross-Pitaevskii equation, we provide the range of validity of our scaling approach and find a very good agreement in the Thomas-Fermi regime. We apply this approach to the study of the scattering of a matter wave packet on a double barrier potential. We show that a Fabry-Perot resonance in such a cavity with an energy width below the pK range can be probed in this manner. We show that our approach can be readily transposed to a large class of many-body quantum systems that exhibit self-similar dynamics.

Current–voltage characteristics of asymmetric double-barrier Josephson junctions

We develop a theory for the current–voltage characteristics of diffusive superconductor-normal metal–superconductor Josephson junctions with resistive interfaces and the distance between the electrodes smaller than the superconducting coherence length. The theory allows for a quantitative analytical and numerical analysis in the whole range of the interface transparencies and asymmetry. We focus on the regime of large interface resistance compared to the resistance of the normal region, when the electron–hole dephasing in the normal region is significant and the finite length of the junction plays a role. In the limit of strong asymmetry we find pronounced current structures at the combination subharmonics of Δ+Δg, where Δg is the proximity minigap in the normal region, in addition to the subharmonics of the energy gap 2Δ in the electrodes. In the limit of rather transparent interfaces, our theory recovers a known formula for the current in a short mesoscopic connector – a convolution of the current through a single-channel point contact with the transparency distribution for an asymmetric double-barrier potential.

Size effect of the subharmonic Shapiro steps on the interference phenomena in the Frenkel-Kontorova model with realistic substrate potentials

Size effect of the subharmonic Shapiro steps on the behavior of harmonic ones is studied in the ac driven overdamped Frenkel-Kontorova model with different types of physically important realistic substrate potentials. The properties of harmonic Shapiro steps are directly correlated with the size of halfinteger steps; and according to that in their amplitude dependence, three distinctive types of behavior have been classified. Our results on other realistic systems show that these classifications are not universal, and that not only the size of halfinteger steps but also the type of the substrate potential determines the properties and correlation between the Shapiro steps. While for some potentials such as variable and double-barrier potential, system evolves through different types of amplitude dependence as the size of halfinteger steps changes, in the case of double-well potential, the system maintains the standard behavior (the behavior for small halfinteger steps) even in the presence of large halfinteger steps.

Transmission of massless Dirac fermions through an array of random scatterers in terms of Fabry-Perot resonances: a Green’s function approach

Transmission properties of massless Dirac fermions that are charge carriers in graphene through a double potential barrier can be completely understood in terms of resonances in Fabry-Perrot cavity. Using a Green’s function based approach we generalize this analysis to the case of transmission through an array of short range random scatterers modeled as delta function. The method helps to understand such disordered transport in terms of well-known optical phenomena such as Fabry-Perot resonances. Using this optical analogy we particularly provide a microscopic understanding of the interplay between disorder-induced localisation that is the hallmark of a non-relativistic system and two important properties of such massless Dirac fermions, namely, complete transmission at normal incidence and periodic dependence of transmission coefficient on the strength of the barrier that leads to a periodic resonant transmission. Within this framework we show that this leads to two different types of conductance behaviour as a function of the system size at the resonant and the off-resonance strengths of the delta function potential.

Effect of DC bias on dielectric properties of nanocrystalline CuAlO2

Grain boundary effect on the room temperature dielectric behavior in mechanically alloyed nanocrystalline CuAlO2 has been investigated using impedance spectroscopy under the applied DC bias voltages 0 V to 4.8 V in a periodic interval of 0.2 V. Analysis of impedance data confirms the existence of double Schottky potential barrier heights (Φb) between two adjacent grains (left and right side) with grain boundary and its influences in dielectric relaxation time (τ), dielectric constant (ɛ′) and dielectric loss (tan δ) factor. Also, clear evidence on the suppression of Φb was demonstrated in the higher applied bias voltages with the parameter τ. At equilibrium state, τ is 0.63 ms and it was reduced to 0.13 ms after the 3.2 V applied DC bias. These observed DC bias voltage effects are obeying ‘brick layer model’ and also elucidates Φb is playing a crucial role in controlling dielectric properties of nanomaterials.

The beam propagation based on one-dimensional separation modulated photonic lattices

We numerically study the propagations of Gaussian beams in four types of separation modulated photonic lattices. The results shows that the potential wells between double positive hyperbolic secant and rectangular potential barriers and between the potential barriers in the forms of double negative hyperbolic secant and rectangular functions can both support localized linear modes. Moreover, the coupling effects between two linear modes in the potential barriers can be used to realize all-optical switch. Furthermore, the nonlinear localization can also be observed in high power. Our results supply new ideas for all optical switch, light controlling and manipulation in photonic lattices.

Crystallite size effect on voltage tunable giant dielectric permittivity of nanocrystalline CuO

The effect of crystallite size and applied DC bias voltage on dielectric permittivity of CuO was studied using impedance spectroscopy. The measurements were performed at room temperature in a wide frequency range of 1 Hz to 1 MHz under applied DC bias voltages from 0 to 3 V in the periodic increment of 0.2 V. The observed applied DC bias voltage effect on giant dielectric constant (ɛ′ = 104) were analyzed with ‘grain boundary double Schottky potential barrier height model’. The percentage of tunability (T %) at the frequency 100 Hz is found to be 45.5% for the case of nanocrystalline CuO in contrast to 0% tunability in bulk CuO.

Tunneling time and stochastic-mechanical trajectories for the double-barrier potential

Abstract Quantum motion of particles tunneling a double barrier potential is considered by using stochastic mechanics. Stochastic-mechanical trajectories give us information about complex motion of tunneling particles that is not obtained within the framework of ordinary quantum mechanics. Using such information, we calculate the tunneling times within each of the barriers which depend on the distance between them. It is found that the stochastic-mechanical tunneling time shows better asymptotic behavior than the quantum-mechanical dwell time and presence time.

Spectrum of localized states in graphene quantum dots and wires

We developed semiclassical method and show that any smooth potential in graphene describing elongated a quantum dot or wire may behave as a barrier or as a trapping well or as a double barrier potential, Fabry–Perot structure, for 1D Schrödinger equation. The energy spectrum of quantum wires has been found and compared with numerical simulations. We found that there are two types of localized states, stable and metastable, having finite life time. These life times are calculated, as is the form of the localized wave functions which are exponentially decaying away from the wire in the perpendicular direction.