Surface Acoustic Solitons - Quantum Theoretical Approach

Zadanie pt. Digitalizacja i udostępnienie w Cyfrowym Repozytorium Uniwersytetu Łódzkiego kolekcji czasopism naukowych wydawanych przez Uniwersytet Łódzki nr 885/P-DUN/2014 zostało dofinansowane ze środków MNiSW w ramach działalności upowszechniającej naukę

Phonon Universal Transmission Fluctuations and Localization in Semiconductor Superlattices with a Controlled Degree of Order

We study both analytically and numerically phonon transmission fluctuations and localization in partially ordered superlattices with correlations among neighboring layers. In order to generate a sequence of layers with a varying degree of order we employ a model proposed by Hendricks and Teller as well as partially ordered versions of deterministic aperiodic superlattices. By changing a parameter measuring the correlation among adjacent layers, the Hendricks- Teller superlattice exhibits a transition from periodic ordering, with alterna- ting layers, to the phase separated opposite limit; including many intermediate arrangements and the completely random case. In the partially ordered versions of deterministic superlattices, there is short-range order (among any $N$ conse- cutive layers) and long range disorder, as in the N-state Markov chains. The average and fluctuations in the transmission, the backscattering rate, and the localization length in these multilayered systems are calculated based on the superlattice structure factors we derive analytically. The standard deviation of the transmission versus the average transmission lies on a {\it universal\/} curve irrespective of the specific type of disorder of the SL. We illustrate these general results by applying them to several GaAs-AlAs superlattices for the proposed experimental observation of phonon universal transmission fluctuations.Comment: 16-pages, Revte

Phonon Transmission Rate, Fluctuations, and Localization in Random Semiconductor Superlattices: Green's Function Approach

We analytically study phonon transmission and localization in random superlattices by using a Green's function approach. We derive expressions for the average transmission rate and localization length, or Lyapunov exponent, in terms of the superlattice structure factor. This is done by considering the backscattering of phonons, due to the complex mass density fluctuations, which incorporates all of the forward scattering processes. These analytical results are applied to two types of random superlattices and compared with numerical simulations based on the transfer matrix method. Our analytical results show excellent agreement with the numerical data. A universal relation for the transmission fluctuations versus the average transmission is derived explicitly, and independently confirmed by numerical simulations. The transient of the distribution of transmission to the log-normal distribution for the localized phonons is also studied.Comment: 36 pages, Late

Gate voltage dependence of a single-electron transistor using the shuttle mechanism

The gate voltage dependence of a single-electron transistor using the shuttle mechanism in which a vibrating conductive nanoparticle carries charges between the electrodes is studied theoretically and with numerical simulations. Two types of gate voltage effect on the transport properties are demonstrated: one is direct modulation of the current via modification in the tunneling rate, giving rise to shift of ] I/]V peaks on the step-like current, splitting of the current steps and periodic behavior of the current with the change in gate voltage. Another is an indirect effect due to a shift in the range of the nanoparticle vibration induced by the gate voltage. The latter effect stops the shuttle mechanism at a large gate voltage, leading to the conduction gap which widens in proportion to the gate voltage

Electron scattering due to confined and extended acoustic phonons in a quantum wire

Electron scattering due to confined and extended acoustic phonons is analytically investigated for a quasi-one-dimensional GaAs quantum wire embedded within bulk AlAs. It is found that the deformation coupling between electrons and confined phonons is extremely small in comparison with that between electrons and extended phonons. Consequently, the electron scattering processes are governed by the extended phonons, and the magnitude and electron energy dependence of the scattering rates are almost the same as those due to the usual three-dimensional bulk phonons

Elastic deformation blockade in a single-electron transistor

A blockade phenomenon for electron transport in a freely suspended single-electron transistor (SET) is predicted. Voltages applied for its operation induce electromechanical forces acting on the SET, giving rise to structural deformation and collapse over a critical voltage. The electric characteristics become sensitive to charge fluctuations on the SET at the onset of the structural instability, leading to changes in the electrical characteristics that hinder electron transport through the SET around the zero-bias-voltage region.RAPID COMMUNICATION

Confined and interface acoustic phonons in a quantum wire

Confined and interface acoustic phonon modes in a cylindrical quantum wire embedded in another material are analytically investigated based on the elastic continuum model by means of the potential theory. Confined acoustic phonon modes are coupled modes of bulk-longitudinal and transverse acoustic waves, classified into torsional, dilatational, and flexural modes due to the rotational symmetry of the modes. Dispersions of the confined modes have subband structures with finite cutoff frequencies owing to quantization of wave vectors in the lateral direction. The density of confined phonon states becomes, as a result, a staircaselike structure. As for the interface modes, regions of material parameters for the possible existence of interface modes are investigated. We found that the existence of interface modes in a quantum wire–surrounding system becomes more sensitive to the combinations of materials than that for a plane interface

Shot-Noise-Induced Random Telegraph Noise in Shuttle Current

Random telegraph noise in the electric current produced by shot noise is predicted for an array of movable colloid particles by Monte Carlo and molecular dynamics calculations. The electron transport is attributed to the shuttle mechanism where moving colloid particles carry charges. The colloid-particle motion induced by the source-drain voltage shows periodic and/or quasiperiodic vibrations, and the current value depends on the vibration modes. Shot noise that is uncorrelated with the colloid-particle motion causes transitions between the periodic and quasiperiodic vibration modes, resulting in random switching between the current levels corresponding to the vibration modes

Resonant acoustic-phonon modes in a quantum wire

We study the extended acoustic-phonon modes in a cylindrical GaAs quantum wire embedded in bulk AlAs. There are two kinds of resonant acoustic-phonon modes related to the wire dimensions: one is entirely extended in the system and the other is almost confined in the wire. Displacement of extended phonon modes in the wire region is enhanced for the resonant modes. The dispersion relations of these resonant modes have subband structures similar to those of confined phonon modes in free-standing wires. Owing to the resonant modes, the extended phonon modes, in the wire region, have characters of confined phonon modes in a free-standing wire rather than the usual bulk phonon modes