Showing papers by "Er'el Granot published in 2022"

Dynamic resonant tunneling via a quasibound superstate

Abstract: The quantum tunneling current via an opaque barrier with an oscillating well reveals a wealth of physical phenomena: eigenstate-assisted activation, the elevator effect, coherent destruction of tunneling, suppression of activation, and the Sisyphus effect are a few examples. In this paper, we investigate these effects from a different perspective---transmission via a quasibound super state (QBSS). It is shown that an oscillating well supports a QBSS, which consists of numerous quasibound substates. Each one of these substates has a finite spectral width, which corresponds to the escape probability. However, they construct a unique spectrum, which consists of activated and suppressed quasi substates all of which are simultaneously excited. Thus, when the oscillating well is integrated into an opaque barrier, one can borrow an analogy from stationary resonant tunneling (RT). In the stationary RT scenario, current flows via a quasibound state. In the oscillating RT scenario, current flows via a QBSS. This analogy can easily explain many of the system's complex behaviors: the symmetry between the current's sensitivity to the incoming energy and the outgoing one, and even why some frequencies induce activation while others suppress it. This analogy can be applied to improve the sensitivity of the system when used for a frequency-controlled transistor for it predicts that when the incoming energy is shifted from the central resonance of the QBSS, the device's current becomes exponentially sensitive to the applied frequency. While the oscillations' frequency mainly determines the spectral distance between substates, the oscillations' amplitude determines the spectral width and center of the QBSS. Furthermore, it is suggested that this analogy can be applied to investigate microbiological systems (the olfactory system) and optical devices.

Derivation of analytical expressions for anomalous reflection in the limit of zero thickness and weakly modulated dielectric grating.

Abstract: It is known that dielectric gratings exhibit anomalous scattering behavior. At certain incident angles, which are not related to the grating's formula, 100% of the incident beam is reflected and, at other angles, 100% is transmitted. In this paper, analytical expressions are derived, for the first time, to the best of our knowledge, for these angles in the regime of narrow grating and weak modulation depth. In these expressions, the parameters emerge from basic principles. Moreover, in this weak modulation regime, a simple and analytically solvable model can be used to derive an analytical expression for the scattered electromagnetic field. Furthermore, it is shown that 100% reflection is achieved even when the grating layer shrinks to zero, the change in the layer's refractive index is zero, and even when the modulation depth is arbitrarily weak, in which case, the incident angle satisfies sin⁡θmin≅±(1-λ/Λ), where Λ is the grating spacing and λ is the beam's wavelength. This result is valid for any ratio λ/Λ. Finally, it is shown that these anomalous transmission behaviors occur even when the modulation coefficient is imaginary and that these analytical expressions are still valid and can predict the corresponding angles.

01 12 16 7 v 1 2 7 D ec 2 00 1 Selected elevation in quantum tunneling

Abstract: The tunneling through an opaque barrier with a strong oscillating component is investigated. It is shown, that in the strong perturbations regime (in contrast to the weak one), higher perturbations rate does not necessarily improve the activation. In fact, in this regime two rival factors play a role, and as a consequence, this tunneling system behaves like a sensitive frequency-shifter device: for most incident particles’ energies activation occurs and the particles are energetically elevated , while for specific energies activation is depressed and the transmission is very low. This effect is unique to the strong perturbation regime, and it is totally absent in the weak perturbation case. Moreover, it cannot be deduced even in the adiabatic regime. It is conjectured that this mechanism can be used as a frequency-dependent transistor, in which the device’s transmission is governed by the external field frequency.