In this paper we analyze the main transport properties of a simple resonant magnetic tunnel junction ͑FM-IS-METAL-IS-FM structure͒ taking into account both elastic and magnon-assisted tunneling processes at low voltages and temperatures near 0 °K.We show the possibility of magnetoresistance inversion as a consequence of inelastic processes and spin-dependent transmission coefficients.Resonant tunneling can also explain the effect of scattering by impurities located inside an insulating barrier.
In this paper we analyze the main transport properties of a simple resonant magnetic tunnel junction ͑FM-IS-METAL-IS-FM structure͒ taking into account both elastic and magnon-assisted tunneling processes at low voltages and temperatures near 0 °K.We show the possibility of magnetoresistance inversion as a consequence of inelastic processes and spin-dependent transmission coefficients.Resonant tunneling can also explain the effect of scattering by impurities located inside an insulating barrier.
We study theoretically transport of a one-dimensional single-channel interacting electron gas through barriers or constrictions. We find that electrons with repulsive interactions, incident upon a single barrier, are completely reflected at zero temperature. At finite temperature (T), the conductance is shown to vanish as a power of T, and at zero temperature, power-law current-voltage characteristics are predicted. For attractive interactions, we predict perfect transmission at zero temperature, with similar power-law corrections. We also study resonant tunneling through a double-barrier structure and related effects associated with the Coulomb blockade. Resonant peaks in the transmission are possible, provided the interactions are not too strongly repulsive. However, in contrast to resonant tunneling in a noninteracting electron gas, we find that in the presence of interactions the width of the resonance vanishes, as a power of temperature, in the zero-temperature limit. Moreover, the resonance line shapes are shown to be described by a universal scaling function, which has power law, but non-Lorentzian tails. For a particular choice of interaction strengths, we present an exact solution of our model, which verifies the scaling assumptions and provides an explicit expression for the scaling function. We also consider the role played by the electron-spin degree of freedom in modifying the trasnsmission through barriers. With spin, there are four possible phases corresponding to perfect transmission or perfect reflection of charge and spin. We present phase diagrams for these different behaviors and analyze the nontrivial transitions between them. At these transitions we find that the conductance or transmission is universal---depending only on the dimensionless conductance of the leads and not on the details of the barriers. In the case of resonant tunneling with spin, we discuss the ``Kondo'' resonance, which occurs when there is a spin degeneracy for electrons between the two barriers. Many of the predictions should be directly testable in gated GaAs wires.
This paper focuses on the quantum tunneling effect, which describes how a particle may penetrate barriers or obstructions using the Schrödinger equation. If a particle makes a barrier tunneling, it means that a particle with low energy goes through the barrier whose energy level is much higher. It is a basis or background for the entire theory of this part. The particle transport probability is explained using both single- and multi-barrier system models. The paper studies the relationship between barrier parameters and particle transmission probability for both single- and multiple-barrier system models.The aim of the study is the provision of the theoretical devices and algorithms via a quantum operational efficiency.Particularly, the paper deals with the multipath barrier tunneling effect, and it connects the transmission coefficients with the system parameters. The goal of this article is to come up with the new strategies and procedures that one can use the quantum phenomenon of the tunneling effect in the contemporary physical th applications, cutting the gap between theoretical physics and technology.This will be done by studying and analyzing theoretical processes and mathematics of this phenomenon along with the technological applications it has.
"A microscopic theory of impurity-assisted tunneling is constructed in which the current-carrying (extended) eigenstates of the average one electron potential in a tunnel junction are utilized as the basis functions which are mixed by the Hamiltonian associated with the presence of a static or dynamic impurity anywhere in the system. In such a system, the one-electron propagator and its concomitant current across the junction easily can be calculated at zero bias by standard techniques for manipulating temperature Green's functions, The presence of a finite bias across the junction is incorporated into the theory via the principle of rigid-occupancy; i.e, the equilibrium occupation of the (current-carrying) many-body eigenstates of the system is taken to be unaffected by the presence of the bias. Therefore the rigid occupancy hypothesis relates the non-equilibrium current flow to the equilibrium (zero-bias) properties of the junction system so that we obtain a theory of nonequilibrium current flow which is not based on linear-response theory, The hypothesis is incorporated into the Matsubara perturbation theory by treating the chemical potentials of the left and right-hand electrodes as separate Lagrangian multipliers determined after the completion of all Matsubara sums to be related by ~=~L-eV. Therefore, for purposes of constructing and solving Dyson's equations for the renormalized one-electron propagators, the theory reduces to the conventional equilibrium theory defined using distorted-wave (i,e. non-plane-wave) states. The usual transfer Hamiltonian results are recovered by expanding the transmission probability. Using this theory, we have constructed and solved the Dysonis equations associated with bare vertex functions for both a static delta-function impurity and dynamic delta-function impurity vibrating at a (Einstein) local mode frequency, All electron-impurity (l~cal-mode-phonon) interactions appear in this formalism as self-energy corrections to the extended-basis electronic wave functions, The position of the impurity relative to the junction-region determines both the sign and magnitude of these corrections, Therefore, the asymmetries in the tunnel characteristics which can be traced to the position of the impurities enter the theory via the asymmetry in the impurity-induced self-energy of the two (i,e, left ~right and right ~ left) linearly-independent current-carrying basis states. Resonant elastic tunneling through impurity states of energy Er near the zero-bias Fermi energy, ,~ causes conductance minima(maxima) for E > r ,(E <'). Zero-bias anomalies in photosensitive GaAs:Au p-n tunnel diodes have been identified with this mechanism. The major new prediction is that resonant elastic impurity-assisted tunneling strongly affects inelastic impurity-assisted tunneling: e,g., if an ""impurity"" state is localized near the oxide in a M-O-S junction then large cusp-like phonon structure in the conductance appears only for majority carrier tunneling from the semiconductor into the metal, This prediction, and its correlation with a zero-bias anomaly is borne out in III-V tunnel diodes and metal-Si:B3P junctions."
Numerical simulations of quantum tunneling with time-dependent barriers show that there is a resonance, with a marked increase in the transmission coefficient. For a raised cosine potential, and for low energies with square barriers, the resonance occurs when a modulation quantum can take a tunneling particle to the top of the barrier. For energies near the top of a square barrier the resonance may be understood by hypothesizing that a tunneling particle may travel from end to end of the barrier until it is ultimately either transmitted or reflected.
We have measured the current-voltage characteristic of a small capacitance tunnel junction coupled to a transmission line resonator. We calibrate the resonator using the sharp resonances displayed by the junction in the superconducting state, which corresponds to the pumping of the modes of the resonator by the ac Josephson current. With this calibration, we explain quantitatively the nonlinearity of the junction characteristic in the normal state as being due to the process by which a single electron tunnels by emitting a photon, the basic process of the theory of the effect of the electromagnetic environment on tunneling.
Quantum tunnelling is a phenomenon in which a particle is able to traverse a potential barrier, even if said particle possesses less energy than the barrier. This process is highly important in many modern fields of physics, such as nuclear physics and semiconductor technology. In this thesis, this phenomenon was presented through analytical study, as well as the derivation of the transmission coefficient in one and three dimensions. Of even greater interest is the phenomenon of resonant tunnelling, where particles tunnel through two or more potential barriers, leading to the formation of quantum wells and quasi-bound energy levels that result in heightened transmission probabilities at certain energies. The transfer matrix method was used in order to find an expression for the resonant tunnelling transmission coefficient in double barrier systems. In addition, a programme was developed in Python in order to investigate resonant tunnelling in different barrier systems. The programme demonstrates how the probability of transmission fluctuates with the energy of the incoming particle, as well as how it is influenced by changes to the framework of the barrier system. Furthermore, effects caused by the inclusion of asymmetry into the system are studied. Finally, the process of spin-dependent tunnelling and the related Rashba spin-orbit coupling were discussed as an extension of the resonant tunnelling phenomenon.