Search Results for « Double-barrier system »

We study theoretically the resonant transmission of acoustic phonons in a double-barrier system for phonons consisting of a bulk material sandwiched between periodic superlattices. The phonon transmission rate and the resonance condition in this system are derived analytically based on the transfer-matrix method. We show that the phonons in a frequency gap of the superlattices can be transmitted through the whole system without attenuation, if the frequency of incident phonons satisfies the resonance condition. Based on the Green's-function method, we also show that the resonant frequencies coincide with the impurity levels associated with the lattice vibrations localized near the embedded bulk layer.

The transmission characteristic of barrierless ABABA multilayer system, where A and B are materials with differing effective masses, is analyzed.The system shows resonant transmission similarly to a conventional double-barrier system, but shows unique features: unity transmission at zero energy, a more structured nature of the transmission versus energy curve and a non-decreasing peak-to-valley ratio with increasing energy.

Copyright c ○ 2013 S. P. Bhattacharya et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A relativistic study on lifetime of resonant tunneling states in the case of the double barrier system consisting of rectangular potential barriers has been studied. This study reveals the fact that as compared to the non-relativistic resonant tunneling states the relativistic resonant states occur in the lower energies but they are having shorter lifetime..

This article investigates the correlation between the optical and transport properties of zinc oxide-zinc magnesium oxide double barrier system by investigating the localization of the energy levels in the quantum well. Effective mass approach is used to investigate this system. The degree of localization of the levels in the quantum well is also examined with respect to the width of the ZnMgO barriers. The energy bands for ZnO/Zn/sub 0.8/Mg/sub 0.2/O structure is also studied.

Abstract Current-voltage (I – V) characteristics in armchair graphene nanoribbon (AGNR) double barrier systems (DBSs) are investigated by the density functional theory (DFT) and the non-equilibrium Green’s function (NEGF) methods. The hexagonal boron nitride (h-BN) which has an analogous structure with a graphene shows wide bandgap and becomes an electrical barrier in DBSs. The heterojunction structure of AGNR and two h-BNs with one six-membered ring width has properties as a resonant tunnelling device. Due to the resonance, sharp peaks are formed in the transmission function around the Fermi energy EF . Our previous studies have explained the origins of some peaks by solving the one-dimensional Dirac equation for massless particles. Here, by using the two-dimensional Dirac equation, we show that the remaining sharp peaks depend on the transverse nodal pattern of the wavefunction as well as the anisotropy of the Fermi velocity. Moreover, in the I – V characteristics, a flat part is formed without the negative differential resistance appearing. By partial density of state (PDOS) analysis, we reveal that the flat part in the current is caused by the fact that the peak positions in the resonance region are stable against the bias voltage.

Abstract A solid-state experiment based on quantum tunneling is proposed to reproduce the natural numbers and prime numbers as resonant tunneling energies in a double barrier system (DBS). For getting the prime numbers as eigenvalues the well potential is considered as the superposition of a smooth potential which is estimated using a semi-classical approach and a weak local fluctuating potential. We use the transfer matrix approach and finite element method by taking only the smooth part of the potential to obtain resonant energies which reproduces the local average prime density and the local average prime gap exactly. The methodology when applied to a quadratic potential of the well, produces whole numbers as eigenvalues except for a constant zero-point energy —the energy levels of a simple harmonic oscillator.

Using a transfer matrix method, we have studied the relationship between the conductance of a harmonically driven quantum dot system and the strength V ac of the time-varying potential in both cases of \hbarω≠Δε and \hbarω= Δε, where ω is the frequency of the time-varying potential and Δε is the energy distance between adjacent resonant levels of the system. In the off-resonance condition (\hbarω≠Δε), it is found that conductance dips appear in the V ac dependence of the sideband conductance instead of the perfect sideband quenching predicted by previous works. Our results show that conductance dips corresponding to the quenching scale with ω-1, while previous theories have suggested that the spectral weight of sideband components is scaled by ω-2 for inhomogeneous time-varying potentials. Under the resonance condition (\hbarω=Δε), our calculation shows the Rabi-type level splitting. The quenching effect of the Rabi-type splitting is also discussed.

Resonant tunneling devices are still under study today due to their multiple applications in optoelectronics or logic circuits. In this work, we review an out-of-equilibrium GaAs/AlGaAs double-barrier resonant tunneling diode system, including the effect of donor density and external potentials in a self-consistent way. The calculation method uses the finite-element approach and the Landauer formalism. Quasi-stationary states, transmission probability, current density, cut-off frequency, and conductance are discussed considering variations in the donor density and the width of the central well. For all arrangements, the appearance of negative differential resistance (NDR) is evident, which is a fundamental characteristic of practical applications in devices. Finally, a comparison of the simulation with an experimental double-barrier system based on InGaAs with AlAs barriers reported in the literature has been obtained, evidencing the position and magnitude of the resonance peak in the current correctly.

We calculate the current and spin torque in small symmetric double tunnel barrier ferromagnet-superconductor-ferromagnet (F-S-F) systems. Spin accumulation in the superconductor governs the transport properties when the spin-flip relaxation time is longer than the transport dwell time. In the elastic transport regime, it is demonstrated that the relative change in the current (spin torque) for F-S-F systems equals the relative change in the current (spin torque) for F-N-F systems upon changing the relative magnetization direction of the two ferromagnets. This differs from the results in the inelastic transport regime where spin accumulation suppresses the superconducting gap and dramatically changes the magnetoresistance [S. Takahashi, H. Imamura, and S. Maekawa, Phys. Rev. Lett. 82, 3911 (1999)]. The experimental relevance of the elastic and inelastic transport regimes, respectively, as well as the reasons for the change in the transport properties are discussed.