Search results for "JUNCTION"
showing 10 items of 862 documents
Image charge dynamics in time-dependent quantum transport
2012
In this work we investigate the effects of the electron-electron interaction between a molecular junction and the metallic leads in time-dependent quantum transport. We employ the recently developed embedded Kadanoff-Baym method [Phys. Rev. B 80, 115107 (2009)] and show that the molecule-lead interaction changes substantially the transient and steady-state transport properties. We first show that the mean-field Hartree-Fock (HF) approximation does not capture the polarization effects responsible for the renormalization of the molecular levels neither in nor out of equilibrium. Furthermore, due to the time-local nature of the HF self-energy there exists a region in parameter space for which …
Generation and Evolution of Spin-, Valley-, and Layer-Polarized Excited Carriers in Inversion-Symmetric WSe2
2016
We report the spin-selective optical excitation of carriers in inversion-symmetric bulk samples of the transition metal dichalcogenide (TMDC) ${\mathrm{WSe}}_{2}$. Employing time- and angle-resolved photoelectron spectroscopy (trARPES) and complementary time-dependent density functional theory (TDDFT), we observe spin-, valley-, and layer-polarized excited state populations upon excitation with circularly polarized pump pulses, followed by ultrafast ($l100\text{ }\text{ }\mathrm{fs}$) scattering of carriers towards the global minimum of the conduction band. TDDFT reveals the character of the conduction band, into which electrons are initially excited, to be two-dimensional and localized wit…
The influence of disorder on the exciton spectra in two-dimensional structures
2019
We study the role of disorder in the exciton spectra in two-dimensional (2D) semiconductors. These can be heterostructures, thin films and multilayers (so-called van der Waals structures) of organometallic perovskites, transition metal dichalcogenides and other semiconductors for optoelectronic applications. We model the disorder by introduction of a fractional Laplacian (with Le´vy index m, defining the degree of disorder) to the Scro¨dinger equation with 2D Coulomb potential. Combining analytical and numerical methods, we observe that the exciton exists only for m 4 1, while the point m = 1 (strongest disorder) corresponds to the exciton collapse. We show also that in the fractional (diso…
Background charge fluctuations in SET-transistors
1996
We have studied fluctuations of background charges in single electron tunnelling (SET) transistors. Changes in the charge distribution of the substrate and other dielectric materials near the transistor cause uncontrolled changes in its conductivity. We have observed big differences in the type and frequency of the conductivity fluctuations between different samples, but no systematic dependence on the substrate material has been found. To obtain information about the location of the source of the charge noise, we performed coincidence measurements on two separate SET transistors which were made very near to each other. The results suggest that the conductivity fluctuations are caused by ch…
The effect of reducing dimensionality on the excitonic recombination in InAs/InP heterostructures
1997
In this work we study the exciton recombination of InAs/InP self-organized quantum dots by means of photolumincscence (PL) as a function of temperature and excitation density. Well defined islands, spatially separated in most cases, and with different size distribution, make localized exciton recombination the dominant contribution to the PL spectrum. From our experimental results, we propose the co-existence of two types of islands, one with small height whose contribution to the PL spectra is important in samples with low InAs coverage (below two monolayers), and the properly 3D islands, whose dimensions and sheet concentration increase with the InAs coverage. Good quality structures are …
Resonant rayleigh scattering in semiconductor structures
1995
A detailed study of the relative role played by localized and/or propagating intermediate excitonic states in, resonant Rayleigh scattering (RRS) is presented for a large set of GaAs quantum well (QW) and bulk structures. We show that the two kinds of states contribute to RRS through different mechanisms. We concluded that RRS occurs via localized states in QW heterostructures, very likely due to localization by the interface roughness, while bulk, crystals turn out to be better candidates for RRS via propagating states.
Triple magnetopolarons in quantum wells
1997
We derive the equations for eigenstates and eigenenergies of a triple magnetopolaron in quantum-well structures. An iteration procedure for obtaining the wave function and energy including the contributions of diagrams with crossing phonon lines is given. We show that under conditions of exact resonance the middle energy branch of the triply split magnetopolaron state consists of only two out of three bare states. We suggest the experimental verification of this prediction.
Solid State Analogue of a Double Slit Interferometer
2002
In a conventional optical double slit interferometer Fig. 1a light emerges from a source at a point O’, passes through two slits A and B and forms an interference pattern at a point O. If the source provides monochromatic radiation the coherence between optical paths O’AO and O’BO is preserved at all reasonable scales. The intensity of the interference pattern at a given point O can be altered by changing the distance ∣O’AO∣ - ∣O’BO∣.
Arrays of Josephson junctions in an environment with vanishing impedance
1999
The Hamiltonian operator for an unbiased array of Josephson junctions with gate voltages is constructed when only Cooper pair tunnelling and charging effects are taken into account. The supercurrent through the system and the pumped current induced by changing the gate voltages periodically are discussed with an emphasis on the inaccuracies in the Cooper pair pumping. Renormalisation of the Hamiltonian operator is used in order to reliably parametrise the effects due to inhomogeneity in the array and non-ideal gating sequences. The relatively simple model yields an explicit, testable prediction based on three experimentally motivated and determinable parameters.
Noise-induced effects in nonlinear relaxation of condensed matter systems
2015
Abstract Noise-induced phenomena characterise the nonlinear relaxation of nonequilibrium physical systems towards equilibrium states. Often, this relaxation process proceeds through metastable states and the noise can give rise to resonant phenomena with an enhancement of lifetime of these states or some coherent state of the condensed matter system considered. In this paper three noise induced phenomena, namely the noise enhanced stability, the stochastic resonant activation and the noise-induced coherence of electron spin, are reviewed in the nonlinear relaxation dynamics of three different systems of condensed matter: (i) a long-overlap Josephson junction (JJ) subject to thermal fluctuat…