Search results for "Hall effect"
showing 10 items of 702 documents
Anharmonicity-induced polaron relaxation in GaAs/InAs quantum dots
2002
The anharmonicity-induced relaxation of a polaron in a quantum dot is analyzed using the Davydov diagonalization method, including the coherent renormalization of the relevant third-order phonon interaction. The resulting relaxation time for a small GaAs/InAs self-assembled quantum dot turns out to be a few times longer than that found previously by a perturbative method.
Coulomb Effects on Few-Body Scattering States
1986
Modifications of stationary momentum space scattering theory, necessitated by the presence of Coulomb forces, are described, both in the formalism which uses unscreened Coulomb potentials and in the screening and renormalization approach. Thereby, emphasis is laid on exposing the conceptual differences, as well as the different, presently achieved status of applicability. Some of the unresolved problems in both methods are enumerated.
Localized surface plasmons on a torus in the nonretarded approximation
2005
International audience; The dispersion relations and field patterns of the localized surface plasmons of a torus are derived analytically in toroidal coordinates in the nonretarded approximation. Numerical calculations are provided in order to identify the conditions under which a toroidal nanostructure supports a significant magnetic dipole moment at optical frequencies.
Optical absorption of torus-shaped metal nanoparticles in the visible range
2007
Received 22 November 2007; published 19 December 2007We theoretically and experimentally investigated the optical response of a thin metal nanotorus in the visiblerange. The close formulas describing the extinction cross sections of a torus are obtained in the nonretardedapproximation. We demonstrate a good agreement between numerical simulations and experimental data. Ourfindings show that the main resonance is highly sensitive to the external medium and the geometrical param-eters of the particle.DOI: 10.1103/PhysRevB.76.245422 PACS number s : 78.67.Bf, 73.20.Mf, 78.20.Ci
Stabilizing spin spirals and isolated skyrmions at low magnetic field exploiting vanishing magnetic anisotropy
2018
Skyrmions are topologically protected non-collinear magnetic structures. Their stability is ideally suited to carry information in, e.g., racetrack memories. The success of such a memory critically depends on the ability to stabilize and manipulate skyrmions at low magnetic fields. The non-collinear Dzyaloshinskii-Moriya interaction originating from spin-orbit coupling drives skyrmion formation. It competes with Heisenberg exchange and magnetic anisotropy favoring collinear states. Isolated skyrmions in ultra-thin films so far required magnetic fields as high as several Tesla. Here, we show that isolated skyrmions in a monolayer of Co/Ru(0001) can be stabilized down to vanishing fields. Eve…
Resonant laser spectroscopy of localized excitons in monolayer WSe_2
2016
Coherent quantum control and resonance fluorescence of few-level quantum systems is integral for quantum technologies. Here we perform resonance and near-resonance excitation of three-dimensionally confined excitons in monolayer WSe2 to reveal near-ideal single-photon fluorescence with count rates up to 3 MHz. Using high-resolution photoluminescence excitation spectroscopy of the localized excitons, we uncover a weakly fluorescent exciton state ∼5 meV blue shifted from the ground-state exciton, providing important information to unravel the precise nature of quantum states. Successful demonstration of resonance fluorescence paves the way to probe the localized exciton coherence in two-dime…
Reliable signal processing using parallel arrays of non-identical nanostructures and stochastic resonance
2010
In the stochastic resonance (SR) phenomena, the response of a non-linear system to a weak periodic input signal is optimised by the presence of a particular level of noise which enhances signal detection. We explore, theoretically, the influence of thermal noise in arrays of metal nanoparticles functionalised with organic ligands acting as tunnelling junctions, with emphasis on the interplay between the SR phenomena and the nanostructure variability. In this system, the transference of a reduced number of electrons may suffice to implement a variety of electronic functions. However, because nanostructures are expected to show a significant variability in their physical characteristics, it i…
High accuracy Raman measurements using the Stokes and anti-Stokes lines
1997
We show that by measuring the separation between the Stokes and anti-Stokes peaks excited by two different laser lines we obtain a very precise determination of absolute phonon energies. The method is useful for measuring small changes of these energies with strain, temperature, laser power, etc. It doubles the changes and avoids the necessity of using the reference lines in the Raman spectra. The method can be applied for the determination of phonon deformation potentials, for the characterization of strained heteroepitaxial layers, and for micro-Raman analysis of strain in silicon integrated circuits. We give examples of phonon shifts in Si, Ge, GaAs, InAs, and GaP as a function of applie…
Optical switching of quantum states inside self-assembled quantum dots
2008
Abstract Photoluminescence and excitation of photoluminescence spectroscopy have been performed for two kinds of single InAs self-assembled quantum dots grown on GaAs. The presence of unintentional impurities (donors and acceptors) offers the possibility to switch from negative to positively charged excitons by selectively exciting impurity related optical transitions.
Isolated self-assembled InAs/InP(001) quantum wires obtained by controlling the growth front evolution
2007
6 páginas, 5 figuras. In this work we explore the first stages of quantum wire (QWR) formation studying the evolution of the growth front for InAs coverages below the critical thickness, θc, determined by reflection high energy electron diffraction (RHEED). Our results obtained by in situ measurement of the accumulated stress evolution during InAs growth on InP(001) show that the relaxation process starts at a certain InAs coverage θRθR this ensemble of isolated nanostructures progressively evolves towards QWRs that cover the whole surface for θ = θc. These results allow for a better understanding of the self-assembling process of QWRs and enable the study of the individual properties of In…