arXiv subjects

Y. Levinson

Publications and source records attributed to Y. Levinson.

At least 19 recordsLinked to original sources

arXiv2008

Auger-like Relaxation of Inter-Landau-Level Magneto-Plasmon Excitations in the Quantised Hall Regime

Auger relaxation in 2D strongly correlated electron gas can be represented as an Auger-like process for neutral magnetoplasmon excitations. The case of "dielectric" state with lack of free electrons (i.e. at integer filling $ν$) is considered. Really the Auger-like process is a coalescence of two magnetoplasmons which are converted into a single one of a different plasmon mode with zero 2D wave-vector. This event turns out to be energetically allowed for magnetoplasmons near their roton minima where the spectrum has the infinite density of states. As a result the additional possibility appears for indirect observation of the magnetorotons by means of anti-Stokes Raman scattering. We find the rate of this process employing the technique of Excitonic Representation for the relevant matrix element calculation.

cond-mat.mes-hall↗

arXiv2008

Relaxation of Inter-Landau-level excitations in the Quatized Hall Regime

Relaxation of collective plasmon inter-Landau-level excitation is determined by emission of LO-phonons or by Auger-like processes when this emission is suppressed off the magneto-phonon resonance conditions. The decay of "one-cyclotron" magneto-plasmons with wave-vectors near the roton minimum is studied under the condition of filling $ν=1$. Some features of this relaxation should be helpful for the experimental detection of the magneto-rotons in a strongly correlated 2D electron gas.

cond-mat.mes-hall↗

arXiv2007

Dephasing due to a fluctuating fractional quantum Hall edge current

The dephasing rate of an electron level in a quantum dot, placed next to a fluctuating edge current in the fractional quantum Hall effect, is considered. Using perturbation theory, we first show that this rate has an anomalous dependence on the bias voltage applied to the neighboring quantum point contact, because of the Luttinger liquid physics which describes the fractional Hall fluid. Next, we describe exactly the weak to strong backscattering crossover using the Bethe-Ansatz solution.

cond-mat.mes-hall↗

arXiv2006

Manipulation of collective spin correlations in semiconductors with polarization squeezed vacuum

We calculate the transfer rate of correlations from polarization entangled photons to the collective spin of a many-electron state in a two-band system. It is shown that when a semiconductor absorbs pairs of photons from a two-mode squeezed vacuum, certain fourth order electron-photon processes correlate the spins of the excited electron pairs of different quasi-momenta. Different distributions of the quantum Stokes vector of the light lead to either enhancement or reduction of the collective spin correlations, depending on the symmetry of the distribution. We find that as the squeezing of the light becomes non-classical, the spin correlations exhibit a crossover from being positive with a $\sim N^2$ ($N$ is average photon number) scaling, to being negative with $\sim N$ scaling, even when $N$ is not small. Negative spin correlations mean a preponderance of spin singlets in the optically generated state. We discuss the possibility to measure the collective spin correlations in a combined measurement of the Faraday rotation fluctuation spectrum and excitation density in a steady-state configuration.

cond-mat.mes-hall↗

arXiv2005

Coherence and Phase in an Electronic Mach-Zehnder Interferometer: An Unexpected Behavior of Interfering Electrons

We report the observation of an unpredicted behavior of interfering 2D electrons in the integer quantum Hall effect (IQHE) regime via a utilization of an electronic analog of the well-known Mach-Zehnder interferometer (MZI). The beauty of this experiment lies in the simplicity of two path interference. Electrons that travel the two paths via edge channels, feel only the edge potential and the strong magnetic field; both typical in the IQHE regime. Yet, the interference of these electrons via the Aharonov-Bohm (AB) effect, behaves surprisingly in a most uncommon way. We found, at filling factors 1 and 2, high visibility interference oscillations, which were strongly modulated by a lobe-type structure as we increased the electron injection voltage. The visibility went through a few maxima and zeros in between, with the phase of the AB oscillations staying constant throughout each lobe and slipping abruptly by at each zero. The lobe pattern and the 'stick-slip' behavior of the phase were insensitive to details of the interferometer structure; but highly sensitive to magnetic field. The observed periodicity defines a 'new energy scale' with an unclear origin. The phase rigidity, on the other hand, is surprising since Onsager relations are not relevant here.

cond-mat.mes-hall↗

arXiv2004

The absorption spectrum around nu=1: evidence for a small size Skyrmion

We measure the absorption spectrum of a two-dimensional electron system (2DES) in a GaAs quantum well in the presence of a perpendicular magnetic field. We focus on the absorption spectrum into the lowest Landau Level around nu=1. We find that the spectrum consists of bound electron-hole complexes, trion and exciton like. We show that their oscillator strength is a powerful probe of the 2DES spatial correlations. We find that near nu=1 the 2DES ground state consists of Skyrmions of small size (a few magnetic lengths).

cond-mat.str-el↗

arXiv2003

Shakeup spectrum in a two-dimensional electron gas in a strong magnetic field

The shakeup emission spectrum in a two-dimensional electron gas in a strong magnetic field is calculated analytically. The case of a localized photocreated hole is studied and the calculations are performed with a Nozieres-De Dominicis-like Hamiltonian. The hole potential is assumed to be small compared to the cyclotron energy and is therefore treated as a perturbation. Two competing many-body effects, the shakeup of the electron gas in the optical transition, and the excitonic effect, contribute to the shakeup satellite intensities. It is shown, that the range of the hole potential essentially influences the shakeup spectrum. For a short range interaction the above mentioned competition is more important and results in the shakeup emission quenching when electrons occupy only the lowest Landau level. When more than one Landau level is filled, the intensities of the shakeup satellites change with magnetic field nonmonotonically. If the interaction is long range, the Fermi sea shakeup processes dominate. Then, the satellite intensities smoothly decrease when the magnetic field increases and there is no suppression of the shakeup spectrum when the only lowest Landau level is filled. It is shown also that a strong hole localization is not a necessary condition for the SU spectrum to be observed. If the hole localization length is not small compared to the magnetic length, the SU spectrum still exists. Only the number of contributions to the SU spectrum reduces and the shakeup processes are always dominant.

cond-mat.str-el↗

arXiv2002

Quantum noise in current biased Josephson junction

Quantum fluctuations in a current biased Josephson junction, described in terms of the RCSJ-model, are considered. The fluctuations of the voltage and phase across the junction are assumed to be initiated by equilibrium current fluctuations in the shunting resistor. This corresponds to low enough temperatures, when fluctuations of the normal current in the junction itself can be neglected. We used the quantum Langevin equation in terms of random variables related to the limit cycle of the nonlinear Josephson oscillator. This allows to go beyond the perturbation theory and calculate the widths of the Josephson radiation lines.

cond-mat.supr-con↗

arXiv2002

Shot-noise in transport and beam experiments

Consider two Fermi gases with the same {\it average} currents: a transport gas, as in solid-state experiments where the chemical potentials of terminal 1 is $μ+eV$ and of terminal 2 and 3 is $μ$, and a beam, i.e., electrons entering only from terminal 1 having energies between $μ$ and $μ+eV$. By expressing the current noise as a sum over single-particle transitions we show that the temporal current fluctuations are very different: The beam is noisier due to allowed single-particle transitions into empty states below $μ$. Surprisingly, the correlations between terminals 2 and 3 are the same.

cond-mat.mes-hall↗

arXiv2002

Quantum noise, detailed balance and Kubo formula in nonequilibrium quantum systems

Current quantum noise can be pictured as a sum over transitions through which the electronic system exchanges energy with its environment. We formulate this picture and use it to show which type of current correlators are measurable, and in what measurement the zero point fluctuations will play a role (the answer to the latter is as expected: only if the detector excites the system.) Using the above picture, we calculate and give physical interpretation of the finite-frequency finite-temperature current noise in a noninteracting Landauer-type system, where the chemical potentials of terminals 1 and 2 are $μ+eV/2$ and $μ-eV/2$ respectively, and derive a detailed-balance condition for this nonequilibrium system. Finally, we derive a generalized form of the Kubo formula for a wide class of interacting nonequilibrium systems, relating the differential conductivity to the current noise.

cond-mat.mes-hall↗

arXiv2002

What quantity is measured in an excess noise experiment?

Consider a measurement in which the current coming out of a mesoscopic sample is filtered around a given frequency, amplified, measured and squared. Then this process is repeated many times and the results are averaged. Often, two such measurements are performed on the same system in and out of equilibrium (the nonequilibrium state can be obtained by a variety of methods, e.g., by applying a DC voltage or electromagnetic radiation to the sample). The excess noise is defined as the difference in the noise between these two measurements. We find that this excess noise is given by the excess of the non-symmetrized power-spectrum of the current-noise. This result holds for a rather general class of experimental setups.

cond-mat.mes-hall↗

arXiv2002

The magnetic response of disordered metallic rings: the large contribution of the far levels

We calculate the orbital linear magnetic response of disordered metallic rings to an Aharonov-Bohm flux using the BCS model for attractive electron-electron interaction. The contribution of all levels including those up to a high energy cutoff results in a much larger value than previously obtained using the local interaction model. The possible relevance of our results to the resolution of the discrepancy between the experimental and theoretical values for the ensemble-averaged persistent currents in these systems is discussed.

cond-mat.mes-hall↗

arXiv2002

Pairing and persistent currents - the role of the far levels

We calculate the orbital magnetic response to Aharonov Bohm flux of disordered metallic rings with attractive pairing interaction. We consider the reduced BCS model, and obtain the result as an expansion of its exact solution to first order in the interaction. We emphasize the connection between the large magnetic response and the finite occupation of high energy levels in the many-body ground state of the ring.

cond-mat.mes-hall↗

arXiv2002

Two pairing parameters in superconducting grains

Unlike bulk superconductivity, where one energy scale, the energy gap, characterizes pairing correlations, we show that in small superconducting grains there exist two different such quantities. The first characterizes cumulative properties of the grain, such as the condensation energy, and the second single-particle properties. To describe these two energy scales, we define two corresponding pairing parameters, and show that although both reduce to the bulk gap for large grains, this occurs at different size scales.

cond-mat.supr-con↗

arXiv2002

Broken unitarity and phase measurements in Aharonov-Bohm interferometers

Aharonov-Bohm mesoscopic solid-state interferometers yield a conductance which contains a term $\cos(ϕ+β)$, where $ϕ$ relates to the magnetic flux. Experiments with a quantum dot on one of the interfering paths aim to relate $β$ to the dot's intrinsic Friedel transmission phase, $α_1$. For closed systems, which conserve the electron current (unitarity), the Onsager relation requires that $β=0$. For open systems, we show that $β$ depends in general on the details of the broken unitarity. Although it gives information on the resonances of the dot, $β$ is generally not equal to $α_1$. A direct relation between $β$ and $α_1$ requires specific ways of opening the system, which are discussed.

cond-mat.mes-hall↗

arXiv2002

Adiabatic transport in nanostructures

A confined system of non-interacting electrons, subject to the combined effect of a time-dependent potential and different external chemical-potentials, is considered. The current flowing through such a system is obtained for arbitrary strengths of the modulating potential, using the adiabatic approximation in an iterative manner. A new formula is derived for the charge pumped through an un-biased system (all external chemical potentials are kept at the same value); It reproduces the Brouwer formula for a two-terminal nanostructure. The formalism presented yields the effect of the chemical potential bias on the pumped charge on one hand, and the modification of the Landauer formula (which gives the current in response to a constant chemical-potential difference) brought about by the modulating potential on the other. Corrections to the adiabatic approximation are derived and discussed.

cond-mat.mes-hall↗

arXiv2001

Reflectionless tunneling in ballistic normal-metal--superconductor junctions

We investigate the phenomenon of reflectionless tunneling in ballistic normal-metal--superconductor (NS) structures, using a semiclassical formalism. It is shown that applied magnetic field and superconducting phase difference both impair the constructive interference leading to this effect, but in a qualitatively different way. This is manifested both in the conductance and in the shot noise properties of the system considered. Unlike diffusive systems, the features of the conductance are sharp, and enable fine spatial control of the current, as well as single channel manipulations. We discuss the possibility of conducting experiments in ballistic semiconductor-superconductor structures with smooth interfaces and some of the phenomena, specific to such structures, that could be measured. A general criterion for the barrier at NS interfaces, though large, to be effectively transparent to pair current is obtained.

cond-mat.supr-con↗

arXiv2001

The Fano Effect in Aharonov-Bohm interferometers

After briefly reviewing the Fano effect, we explain why it may be relevant to various types of Aharonov-Bohm interferometers. We discuss both closed (electron conserving) and open interferometers, in which one path contains either a simple quantum dot or a decorated quantum dot (with more than one internal state or a parallel path). The possible relevance to some hitherto unexplained experimental features is also discussed.

cond-mat.mes-hall↗