Time-dependent transport in interacting mesoscopic systems

We review recent applications of the nonequilibrium Green function technique to time-dependent transport in mesoscopic systems.Comment: Submitted to "Progress in Nonequilibrium Green's Functions", Ed. M. Bonitz, World Scientific; 24 pages, 7 figures, uses sprocl.sty (included) Revised version (misprints corrected, added two references

Dynamical Franz-Keldysh effect

We introduce and analyze the properties of dynamical Franz-Keldysh effect, i.e. the change of density-of-states, or absorption spectra, of semiconductors under the influence of {\it time-dependent} electric fields. In the case of a harmonic time-dependence, we predict the occurence of significant fine structure, both below and above the zero-field band-gap, which should be experimentally observable.Comment: 4 pages, REVTEX 3.0, uses epsf, 5 figures attached as Z-compressed .tar fil

Simple models suffice for the single dot quantum shuttle

A quantum shuttle is an archetypical nanoelectromechanical device, where the mechanical degree of freedom is quantized. Using a full-scale numerical solution of the generalized master equation describing the shuttle, we have recently shown [Novotn\'{y} {\it et al.}, Phys. Rev. Lett. {\bf 92}, 248302 (2004)] that for certain limits of the shuttle parameters one can distinguish three distinct charge transport mechanisms: (i) an incoherent tunneling regime, (ii) a shuttling regime, where the charge transport is synchronous with the mechanical motion, and (iii) a coexistence regime, where the device switches between the tunneling and shuttling regimes. While a study of the cross-over between these three regimes requires the full numerics, we show here that by identifying the appropriate time-scales it is possible to derive vastly simpler equations for each of the three regimes. The simplified equations allow a clear physical interpretation, are easily solved, and are in good agreement with the full numerics in their respective domains of validity.Comment: 23 pages, 14 figures, invited paper for the Focus issue of the New Journal of Physics on Nano-electromechanical system

Phase measurement of photon-assisted tunneling through a quantum dot

Recent double-slit interference experiments have demonstrated the possibility of probing the phase of the complex transmission coefficient of a quantum dot via the Aharonov-Bohm effect. We propose an extension of these experiments: an ac voltage imposed on the side gate with the concomitant photonic sidebands leads to additional structure both in the amplitude and in the phase of the Aharonov-Bohm signal. Observation of these effects would be a definitive proof of coherent absorption and reemission of photons from the ac source.Comment: 6 pages using latex2e and EuroPhys.sty. Uses epsf to include 5 figures (submitted to Europhys. Lett.

Transport in semiconductor superlattices: from quantum kinetics to terahertz-photon detectors

Semiconductor superlattices are interesting for two distinct reasons: the possibility to design their structure (band-width(s),doping, etc.) gives access to a large parameter space where different physical phenomena can be explored. Secondly, many important device applications have been proposed, and then subsequently successfully fabricated. A number of theoretical approaches has been used to describe their current-voltage characteristics, such as miniband conduction, Wannier-Stark hopping, and sequential tunneling. The choice of a transport model has often been dictated by pragmatic considerations without paying much attention to the strict domains of validity of the chosen model. In the first part of this paper we review recent efforts to map out these boundaries, using a first-principles quantum transport theory, which encompasses the standard models as special cases. In the second part, focusing in the mini-band regime, we analyze a superlattice device as an element in an electric circuit, and show that its performance as a THz-photon detector allows significant optimization, with respect to geometric and parasitic effects, and detection frequency. The key physical mechanism enhancing the responsivity is the excitation of hybrid Bloch-plasma oscillations.Comment: 22 pages, 10 figures, uses lamuphys.sty (included); to appear in the Proceedings of the XVI Sitges Conference, Statistical and Dynamical Aspects of Mesoscopic Systems (Lecture Notes in Physics, Springer

Microscopic theory of indistinguishable single-photon emission from a quantum dot coupled to a cavity: The role of non-Markovian phonon-induced decoherence

We study the fundamental limit on single-photon indistinguishability imposed by decoherence due to phonon interactions in semiconductor quantum dot-cavity QED systems. Employing an exact diagonalization approach we find large differences compared to standard methods. An important finding is that short-time non-Markovian effects limit the maximal attainable indistinguishability. The results are explained using a polariton picture that yields valuable insight into the phonon-induced dephasing dynamics.Comment: published version, comments are very welcom

Shuttle instabilities: semiclassical phase analysis

We present a semiclassical analysis of the instability of an electron shuttle composed of three quantum dots: two are fixed and coupled via leads to electron resevoirs at different chemical potentials, while the central dot is mounted on a classical harmonic oscillator. The semiclassical analysis, which is valid if the central dot oscillation amplitude is larger than the quantum mechanical zero point motion, can be used to gain additional insight about the relationship of resonances and instabilities of the device.Comment: 4 pages, 3 figures, presented at EP2DS-15, Nara, July 200

Plasmons in dimensionally mismatched Coulomb coupled graphene systems

We calculate the plasmon dispersion relation for Coulomb coupled metallic armchair graphene nanoribbons and doped monolayer graphene. The crossing of the plasmon curves, which occurs for uncoupled 1D and 2D systems, is split by the interlayer Coulomb coupling into a lower and an upper plasmon branch. The upper branch exhibits a highly unusual behavior with endpoints at finite $q$. Accordingly, the structure factor shows either a single or a double peak behavior, depending on the plasmon wavelength. The new plasmon structure is relevant to recent experiments, its properties can be controlled by varying the system parameters, and be used in plasmonic applications.Comment: 5 pages, 3 figures; in press in Phys. Rev. Let

Wave packet approach to periodically driven scattering

For autonomous systems it is well known how to extract tunneling probabilities from wavepacket calculations. Here we present a corresponding approach for periodically time-dependent Hamiltonians, valid at all frequencies, field strengths, and transition orders. After mapping the periodically driven system onto a time-independent one with an additional degree of freedom, use is made of the correlation function formulation of scattering [J. Chem. Phys. {\bf 98}, 3884 (1993)]. The formalism is then applied to study the transmission properties of a resonant tunneling double barrier structure under the influence of a sinusoidal laser field, revealing an unexpected antiresonance in the zero photon transition for large field strengths.Comment: 4 pages, 2 figure

Current and current fluctuations in quantum shuttles

We review the properties of electron shuttles, i.e. nanoelectromechanical devices that transport electrons one-by-one by utilizing a combination of electronic and mechanical degrees of freedom. We focus on the extreme quantum limit, where the mechanical motion is quantized. We introduce the main theoretical tools needed for the analysis, e.g. generalized master equations and Wigner functions, and we outline the methods how the resulting large numerical problems can be handled. Illustrative results are given for current, noise, and full counting statistics for a number of model systems. Throughout the review we focus on the physics behind the various approximations, and some simple examples are given to illustrate the theoretical concepts. We also comment on the experimental situation.Comment: Minireview; technical level aimed at general audience, based on an invited talk at "Transport Phenomena in Micro and Nanodevices", October 17-21 Kona, Hawai