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We demonstrate that an off-resonant circularly polarized light-modulated double-barrier monolayer ${\mathrm{WSe}}_{2}$ junction can operate as a valley filter and a valley valve simultaneously. Spin-, valley-, and energy-dependent line-type resonant peaks appear in the transmission spectrum, and the splitting of the valley degree of freedom due to the coupling between the light-induced gap and the valley index is also present. By fixing the light on the first barrier, the valley switch can be controlled efficiently by the optical field on the second one. Furthermore, the gate voltage can adjust not only the conductance but also the operation window of the valley filter. The proposed junction provides insight into the manipulation of valley degree of freedom based on ${\mathrm{WSe}}_{2}$ and other transition metal dichalcogenides.

We show that the presence of a side-attached state strongly modifies the transmission through a one-dimensional double-barrier system in the window of wave vectors around the Fano antiresonance. Specifically, the interplay between the Fano interference and the size quantization inside the structure gives rise to narrow resonant peaks in the transmission coefficient. The height of the peaks may become close to unity (perfect transmission) even for an asymmetric setup with strong barriers, where the transmission coefficient in the absence of the Fano state is strongly suppressed at all other wave vectors. Thus, the two types of interference phenomena, each by itself leading to the suppression of the transmission, conspire in a peculiar way to produce the transparency enhancement.

We study the resistance states and spin dynamics in a Ag/Fe(8)/MgO(3)/Fe(8)/MgO(5)/Fe/Ag junction based on a first-principles scattering theory. Spin dynamics simulations show that up to four resistance states with noticeable difference can be achieved via manipulating the voltage bias scheme and the position of the reference magnetization. The study indicates possible multiple-valued logic applications in an asymmetric MgO-based double-barrier magnetic tunnel junction.

The Co-Fe-B/MgO system with perpendicular magnetic anisotropy finds extensive application in modern magnetic memories. Critical issues for the practical usage of magnetic tunnel junctions (MTJs) include the limited thermal stability of bit storage, and low switching efficiency. This study elucidates the deterministic influence of Co-Fe-B composition and the MgO interface on an MTJ's fundamental magnetic properties, which affect both thermal stability and switching current. Furthermore, the authors observe an anomalous trend in saturation magnetization, which is attributed to a change in magnetic anisotropy.

Shot noise reveals spin dependent transport properties in a magnetic tunnel junction. We report measurement of shot noise in CoFeB/MgO/CoFeB/MgO/CoFeB double barrier magnetic tunnel junctions, which shows a strong temperature dependence. The Fano factor used to characterize shot noise increases with decreasing temperature. A sequential tunneling model can be used to account for these results, in which a larger Fano factor results from larger spin relaxation length at lower temperatures.

The generalized Hartmann effect (GHE) predicts a strict inequality between the traversal times across a contiguous and a separated double-barrier system. This is compared to the implications of the time-of-arrival (TOA) operator approach to barrier traversal time [E. A. Galapon, Phys. Rev. Lett. 108, 170402 (2012)]. It is shown that, for initial wave packets with compact supports in the far incident side of the barrier system, the expectation value of the traversal time is independent of the separation between the barriers. On the other hand, for wave packets with supports extending inside the first barrier, the contribution of the barrier separation to the traversal time exponentially increases with the barrier height. Our result shows that if the support of the incident wave packet is far from the barrier region, the GHE inequality is violated. However, if the support of the wave packet extends inside the barrier region, the GHE inequality is consistent with the TOA operator approach, but only when the particle's incident energy is very small.

A new sustained high-performance regime, combining discrete edge and core transport barriers, has been discovered in the DIII-D tokamak. Edge localized modes (ELMs) are replaced by a steady oscillation that increases edge particle transport, thereby allowing particle control with no ELM-induced pulsed divertor heat load. The core barrier resembles those usually seen with a low (L) mode edge, without the degradation often associated with ELMs. The barriers are separated by a narrow region of high transport associated with a zero crossing in the E x B shearing rate.

The general solution for ballistic electronic transport through double-barrier Josephson junctions is derived. We show the existence of a regime of phase-coherent transport in which the supercurrent is proportional to the single barrier transparency and the way in which this coherence is destroyed for increasing interlayer thickness. The quasiparticle dc current at arbitrary voltage is determined., 4 pages, 2 figures, submitted to Phys. Rev. B

Enhancement of the magnitude of the value corresponding to the superconducting energy gap of Al${}^{\ensuremath{'}}$ in Nb/Al-AlO${}_{x}$-Al${}^{\ensuremath{'}}$-AlO${}_{x}$-Al/Nb and Nb/Al/Nb/Al-AlO${}_{x}$-Al${}^{\ensuremath{'}}$-AlO${}_{x}$-Al/Nb/Al/Nb devices by tunnel extraction of quasiparticles has been investigated experimentally. The enhancement is observed both at the gap-difference and gap-sum voltage. In addition to the gap-difference and gap-sum features, there is a feature in the $I$-$V$ characteristic which corresponds to the sum of the energy gaps of the external electrodes. The dc and ac Josephson currents appear in the devices below the same critical temperature ${T}_{\mathrm{c}\mathrm{}\mathrm{eq}},$ which is found to be ${T}_{\mathrm{c}\mathrm{}\mathrm{eq}}=2.35$ and 2.60 K for the devices of the first and second types, respectively. Below ${T}_{\mathrm{c}\mathrm{}\mathrm{eq}},$ an enhancement of the dc component of ac Josephson current has been observed at $Vg0$, as compared with the magnitude of the dc Josephson current at $V=0$.

We report on the realization of a double barrier resonant tunneling diode for cavity polaritons, by lateral patterning of a one-dimensional cavity. Sharp transmission resonances are demonstrated when sending a polariton flow onto the device. We use a non-resonant beam can be used as an optical gate and control the device transmission. Finally we evidence distortion of the transmission profile when going to the high density regime, signature of polariton-polariton interactions., Comment: 5 pages, 4 figures

We report the observation of resonant tunneling through CdTe/${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mg}}_{\mathit{x}}$Te double barrier, single-quantum-well heterostructures. Pronounced negative differential resistance has been observed in the current-voltage characteristics with peak-to-valley ratios up to 8:1 at 4.2 K. Vertical transport across the double barrier has been analyzed in detail as a function of temperature and applied magnetic fields. \textcopyright{} 1996 The American Physical Society.

In this work, we have numerically integrated in space and time the effective-mass Schr\"odinger equation for an electron-hole pair in a GaAs/AlAs double-barrier heterostructure. Considering the electron-phonon interaction and an external electric field, we have studied the excitonic tunneling escape process from the double-barrier quantum well. In this way, electronic lifetimes have been obtained at different well widths and applied electric fields.

By means of hydrostatic pressure, the bottom of the conduction band of GaSb can be displaced from the \ensuremath{\Gamma} point in the Brillouin zone to the L point. We have used this effect to control the nature of the electrons (\ensuremath{\Gamma} or L) available for tunneling at the electrodes of GaSb-AlSb-GaSb-AlSb-GaSb double-barrier heterostructures. In a structure grown along the (100) direction, we have observed negative differential resistance features due to resonant tunneling through two different paths: from the \ensuremath{\Gamma} valley in the electrodes through the first quantized \ensuremath{\Gamma} state in the well and from the L valley in the electrodes through the first and second L states in the well. In a structure grown along the (111) direction, only resonant tunneling via the \ensuremath{\Gamma} path has been observed.

Based upon Keldysh nonequilibrium Green functions, a theoretical formalism is developed to study the current-noise characteristics of one-dimensional double-barrier heterostructures. The effects of the Coulomb blockade on the I-V curve and on the current fluctuation is studied. For the static case a reduction of the full shot noise is observed. A connection between the noise frequency dependence and the transit time of the electron going through the structure is established.

The dc current in a biased double-barrier resonant-tunneling structure is calculated using a nonequilibrium Green's-function formalism. Realistic models involving well, barrier, and interface modes are employed to evaluate the phonon-assisted components of the current. The calculated dc current agrees well with experimental data for a GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As resonant-tunneling structure. The observed phonon-replica peak in the I-V characteristics is attributed to the emission of GaAs-confined modes in the well and AlAs-like symmetric interface modes. The effect of the nonequilibrium well-occupation function is shown to be small. For the ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Al}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As resonant-tunneling structure, phonon scattering becomes comparable to alloy-well scattering at about 200 K.

In this paper we report the results of extensive magnetotransport experiments on asymmetric GaAs/AlAs double-barrier structures that were specifically designed to possess large phonon-assisted tunneling currents. We find quantitative agreement between measured valley currents at liquid-helium temperature and calculations that include the effects of phonon localization using the dielectric-continuum model. The results demonstrate that (1) a major part of the valley current in these structures is due to phonon-assisted tunneling, and (2) symmetric-interface phonons and confined phonons in the GaAs well are the most important in phonon-assisted tunneling processes

A theoretical analysis has been carried out to compare the tunneling processes in a double-quantum-well three-barrier (DQW-TB) system and a single-quantum-well double-barrier (SQW-DB) system. Based on a general WKB formula, it is shown that a symmetric DQW-TB system with transparencymatched barriers is far superior to the SQW-DB system in a number of aspects, including the peak current, the peak-to-valley ratio, and the speed limit

The lifetime τ e of an electron occupying the quasibound state in an Al x Ga 1-x As/GaAs doublebarrier structure has been calculated with both the tunneling Hamiltonian approach and the complex eigenvalue method. It is found that τ e is dominated by the barrier width, but is insensitive to the well width and the bias. We have also investigated the effect of the electron-LO-phonon interaction on the dynamics of the electron in the quasibound state

The effects of Coulomb interactions on the transport properties of the relativistic electron through graphene-based double-barrier structures have been investigated. A self-consistent Green's function method has been developed by solving numerically the Dyson equation in the Hartree-Fock approximation. The transmission probability, conductivity, shot noise, and Fano factor through the structures have been calculated and analyzed. It is shown that Klein tunneling is suppressed strongly by taking into account the electron-electron interaction. In contrast, the Fano factor shows abrupt increase. The shot noise is either improved or suppressed, which depends on the energy of the incident electron and the strength of the electron-electron interaction. The physical originations for these phenomena have been discussed.

We reexamine the Salecker-Wigner-Peres clock formalism and show that it can be directly applied to the phenomenon of tunneling. Then we apply this formalism to the determination of the tunneling time of a nonrelativistic wave packet, sharply concentrated around a tunneling energy, incident on a symmetric double-barrier potential. In order to deepen the discussion about the generalized Hartman effect, we consider the case in which the clock runs only when the particle can be found inside the region between the barriers and show that, whenever the probability to find the particle in this region is non-negligible, the corresponding time (which in this case turns out to be a dwell time) increases with barrier spacing.

We suggest a simple approach for studying the quasi-bound fermion states induced by one-dimensional potentials in graphene. Detailed calculations have been performed for symmetric double barrier structures and $n\text{\ensuremath{-}}p\text{\ensuremath{-}}n$ junctions. Besides the crucial role of the transverse motion of carriers, we systematically examine the influence of different structure parameters such as the barrier width in double barrier structures or the potential slope in $n\text{\ensuremath{-}}p\text{\ensuremath{-}}n$ junctions on the energy spectrum and, especially, on the resonant-level width and, therefore, the localization of quasi-bound states.

En utilisant la formule de Kubo pour la conductivite electrique, et un Hamiltonien de la liaison forte represente sur un reseau de Bethe, on developpe un formalisme pour etudier les proprietes electroniques et de transport des structures amorphes a double barrieres. Analyse des effets de taille quantiques en fonction des parametres de l'heterostructure. Comparaison des resultats theoriques avec les courbes I-V experimentales

Les magneto-oscillations du courant dans la situation de resonance montrent la bidimensionnalite des electrons de la source resultant de la formation d'une couche d'accumulation dans l'emetteur. On observe trois ensembles differents des oscillations du courant en regime hors resonance: effet tunnel avec des processus de diffusion elastique ou non et modulation de charge de la couche d'accumulation

Etude de l'interference quantique a travers ces structures, de la distribution hors equilibre des electrons de l'effet tunnel conduits par la tension de polarisation appliquee, et de l'effet des reservoirs (electrodes). Le comportement transitoire du courant d'effet tunnel est caracterise par le processus de construction des electrons de l'effet tunnel dans le puits quantique. La partie imaginaire de l'admittance est liee a la conductance par la relation de Kronig-Kramers

We report on the noise characteristics of double-barrier resonant-tunneling structures obtained from systematic noise measurements on three samples with different barrier structures. Our results provide direct evidence of incoherent tunneling and can be qualitatively understood if phase incoherence of the tunneling processes is taken into account.

Quantum well (QW) resonances in Fe(001)/MgO/Fe/MgO/Fe double barrier magnetic tunnel junctions are calculated from first principles. By including the Coulomb blockade energy due to the finite size islands of the middle Fe film, we confirm that the oscillatory differential resistance observed in a recent experiment [T. Nozaki, Phys. Rev. Lett. 96, 027208 (2006)10.1103/PhysRevLett.96.027208] originates from the QW resonances from the Delta1 band of the Fe majority-spin channel. The primary source of smearing at low temperatures is shown to be the variation of the Coulomb blockade energy.

The lateral conductivity of the middle Al layer of a $\mathrm{Nb}∕\mathrm{Al}∕\mathrm{Al}{\mathrm{O}}_{x}∕\mathrm{Al}∕\mathrm{Al}{\mathrm{O}}_{x}∕\mathrm{Al}∕\mathrm{Nb}$ (SINIS) multiterminal device is studied as a function of the current injected perpendicular to the layers in a regime where a gap-difference-like feature is observed in the current-voltage characteristic. The response of the Al layer does not confirm an earlier reported observation of superconductivity in the Al far above its transition temperature [Blamire et al., Phys. Rev. Lett. 66, 220 (1991)].

Recent papers suggest that tunneling wave packets traverse the region of allowed propagation between two potential barriers with superluminal group velocity and in a time independent of barrier separation. This phenomenon has been termed the ``generalized Hartman effect'' and extended to multiple barriers. Here we show that this delay time is not a transit time but a cavity lifetime. It does not imply superluminal velocity. Reported experimental verifications of this effect are reinterpreted.

We present a general treatment to study transport phenomena in systems described by tight-binding Hamiltonians coupled to reservoirs and with one or more time-periodic potentials. We apply this treatment to the study of transport phenomena in a double barrier structure with one and two harmonic potentials. Among other properties, we discuss the origin of the sign of the net current., To appear in PRB