Results 1 - 10 of 4325
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[en] Scanning gate microscopy is used to find the position of a quantum Hall island (QHI) which controls the electron transport through a mesoscopic quantum ring. Such QHIs emerging around potential inhomogeneities are tunnel-coupled with edge states. Approaching a polarized metallic tip over the QHIs gradually changes their surface and generates Coulomb blockade oscillations. This mechanism permits the identification of the center of the QHIs. Here, by sweeping the distance between the tip and the two dimensional electron gas, we clearly locate the center of an individual QHI
[en] The effect of strong singularity in the calculation of range function for the RKKY interaction in 1D electron gas is discussed. The method of handling this singularity is presented. A possible way of avoiding the singularity in the Ruderman–Kittel perturbation theory in 1D is described.
[en] We introduce the concept of electrophobic interaction, analogous to hydrophobic interaction, for describing the behavior of impurity atoms in a metal, a “solvent of electrons”. We demonstrate that there exists a form of electrophobic interaction between impurities with closed electron shell structure, which governs their dissolution behavior in a metal. Using He, Be and Ar as examples, we predict by first-principles calculations that the electrophobic interaction drives He, Be or Ar to form a close-packed cluster with a clustering energy that follows a universal power-law scaling with the number of atoms (N) dissolved in a free electron gas, as well as W or Al lattice, as E_c ∝ (N"2"/"3−N). This new concept unifies the explanation for a series of experimental observations of close-packed inert-gas bubble formation in metals, and significantly advances our fundamental understanding and capacity to predict the solute behavior of impurities in metals, a useful contribution to be considered in future material design of metals for nuclear, metallurgical, and energy applications.
[en] The small-rsub(s) expansion is derived for the positron correlation energy and annihilation rate in a homogeneous electron gas. The correlation energy is found to be μ = -1.563 x rsub(s)sup(-1/2) + 0.051 (ln rsub(s))2 -0.098 ln rsub(s) + 0.976 + higher terms. (author)
[en] We present a systematic study of the microwave-induced oscillations in the magnetoresistance of a two-dimensional electron gas for mixed disorder including both short-range and long-range components. The obtained photoconductivity tensor contains contributions of four distinct transport mechanisms. We show that the photoresponse depends crucially on the relative weight of the short-range component of disorder. Depending on the properties of disorder, the theory allows one to identify the temperature range within which the photoresponse is dominated by one of the mechanisms analyzed in the paper.
[en] We report on a theoretical study of the commensurability oscillations in a quasi-two-dimensional electron gas modulated by a unidirectional periodic potential and subject to tilted magnetic fields with a strong in-plane component. As a result of coupling of the in-plane field component and the confining potential in the finite-width quantum well, the originally circular cyclotron orbits become anisotropic and tilted out of the sample plane. A quasi-classical approach to the theory, that relates the magneto-resistance oscillations to the guiding-center drift, is extended to this case.
[en] The onset is described on the example of neon of a transition from a non-hydrodynamic state of the electron gas, which exists at low pressures and currents, to a state where a local hydrodynamics is applicable. In the non-hydrodynamic state the ionization waves are influenced by the resonant properties of the electron gas which means that several varieties can be selected on each of the two dispersion curves. With increasing current the two parts of dispersion curve of the fast varieties (r and s) merge and this is interpreted as the disappearance of the spatial resonance of the electron gas due to an enhancement of electron Coulomb collisions. (author)
[en] Current fluctuations in ballistic quantum point contacts attract now much attention, both in theory and experiment partly because of the assumed possibility to measure fractional charges in shot-noise and to probe other non Fermi liquid properties. We are interested in current fluctuations in a ballistic point contacts biased by applied voltage and irradiated by external field. Time averaged current in microstructures under such conditions (photon-assisted current) was investigated experimentally in point contacts and quantum dots. We consider a classical field which can be coherent (e.g. microwave radiation) or incoherent (e.g. representing the environment at high enough temperature or a heat phonon pulse). We assume that the field does not irradiate the leads between which the bias is applied. Which means e.g. modulated gate voltage, not modulated bias voltage. We model this situation considering a 1D channel with a time-dependent barrier potential U(x, t). The d.c. part of the potential U0(x) is due to the squeezing of the point contacts while the a.c. part JδU(x, t) is due to the field. We suggest a new approach to calculate current and current correlations in such a system. The approach is based on the concept of scattering states for a time dependent Hamiltonian. Consider the 1D Schroedinger equation i(∂/∂t)ψ = Hψ for one particle with a time dependent Hamiltonian H = -∇2/2m + U(x,t), where the barrier potential U(x,t) = 0 at x->→ ±∞ for all t. For any energy εk ≡ k2/2m > 0 (with k > 0) we define time dependent scattering states Χσk(x,t),σ = ±, as solutions of the Schroedinger equation with the following boundary conditions: the only incoming waves are e-iεkt+ikx for Χ+k e-iεkt-ikx for Χ-k. The outgoing parts of Χ+k contain waves with k' ≠ k, describing inelastic scattering in transmission and reflection by the a.c. barrier. The time-dependent electron field operator can be calculated in the following way: Ψ(x,t) ΣkσσσkΧσk(x,t), where σσσk are Fermi operators of electrons in the left lead and the right lead at x = ±∞, respectively. Electrons in different leads do not correlate, while averages for operators belonging to the same lead can be calculated as for a free Fermi gas with chemical potentials μ± introducing the bias voltage V = (μ+ - μ-)/e. Using this approach we calculated the spectra of the current noise in a biased contact irradiated by a weak random field. Considered examples demonstrate that the nonequilibrium noise excited by irradiation differs essentially from nonequilibrium noise excited by bias