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The evolution of the fractional quantum Hall state at filling 5/2 is studied in density tunable two-dimensional electron systems formed in wide wells in which it is possible to induce a transition from single to two subband occupancy. In... more
The evolution of the fractional quantum Hall state at filling 5/2 is studied in density tunable two-dimensional electron systems formed in wide wells in which it is possible to induce a transition from single to two subband occupancy. In 80 and 60 nm wells, the quantum Hall state at 5/2 filling of the lowest subband is observed even when the
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ABSTRACT We study the effect of spatial correlation of ionized donors on the single-particle scattering time and on spin splitting in a two-dimensional electron gas (2DEG). As the correlation is being reduced we observe a reduction in the... more
ABSTRACT We study the effect of spatial correlation of ionized donors on the single-particle scattering time and on spin splitting in a two-dimensional electron gas (2DEG). As the correlation is being reduced we observe a reduction in the scattering time and a collapse of the spin-splitted peaks into a single peak. We find these electronic properties to be much more sensitive than the momentum relaxation time (or mobility) in high mobility 2DEG. We compare our results with Monte Carlo simulations and find them to be in partial agreement.
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ABSTRACT Low temperature, high magnetic field experiments were carried out with monochromatic terahertz (THz) sources to reveal multimode spectra of magnetoplasmons excited in gated and ungated samples processed on a high electron... more
ABSTRACT Low temperature, high magnetic field experiments were carried out with monochromatic terahertz (THz) sources to reveal multimode spectra of magnetoplasmons excited in gated and ungated samples processed on a high electron mobility GaAs/AlGaAs heterostructure. We show that playing with the geometry and thickness of the gate one can control both the plasmon dispersion relation and selection rules for plasmon excitation, giving a tool to a better control of plasmon resonances in THz detectors. (C) 2014 AIP Publishing LLC.
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Electron pairing is a rare phenomenon appearing only in a few unique physical systems; for example, superconductors and Kondo-correlated quantum dots. Here, we report on an unexpected electron pairing in the integer quantum Hall effect... more
Electron pairing is a rare phenomenon appearing only in a few unique physical systems; for example, superconductors and Kondo-correlated quantum dots. Here, we report on an unexpected electron pairing in the integer quantum Hall effect regime. The pairing takes place within an interfering edge channel in an electronic Fabry-Perot interferometer at a wide range of bulk filling factors, between 2 and 5. We report on three main observations: high-visibility Aharonov-Bohm conductance oscillations with magnetic flux periodicity equal to half the magnetic flux quantum; an interfering quasiparticle charge equal to twice the elementary electron charge as revealed by quantum shot noise measurements, and full dephasing of the pairs' interference by induced dephasing of the adjacent inner edge channel-a manifestation of inter-channel entanglement. Although this pairing phenomenon clearly results from inter-channel interaction, the exact mechanism that leads to electron-electron attraction ...
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Abstract. We study the dependence of the photoluminescence decay of the negatively charged exciton on the electron concentration for different excitation energies. The radiative lifetime of the trion, directly measured when exciting the... more
Abstract. We study the dependence of the photoluminescence decay of the negatively charged exciton on the electron concentration for different excitation energies. The radiative lifetime of the trion, directly measured when exciting the trion resonantly, is found to be constant for the studied concentration range from about 3 x 1010 cm'2 upwards.
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ABSTRACT Coulomb exchange interactions of electrons in the nu=3 quantum Hall state are determined from two inter-Landau level spin-flip excitations measured by resonant inelastic light scattering. The two coupled collective excitations... more
ABSTRACT Coulomb exchange interactions of electrons in the nu=3 quantum Hall state are determined from two inter-Landau level spin-flip excitations measured by resonant inelastic light scattering. The two coupled collective excitations are linked to inter-Landau level spin-flip transitions arising from the N=0 and N=1 Landau levels. The strong repulsion between the two spin-flip modes in the long-wave limit is clearly manifested in spectra displaying Coulomb exchange contributions that are comparable to the exchange energy for the quantum Hall state at nu=1. Theoretical calculations within the Hartree-Fock approximation are in a good agreement with measured energies of spin-flip collective excitations.
The quantum eraser is a device that illustrates the quantum principle of complementarity and shows how a dephased system can regain its lost quantum behavior by erasing the "which-path" information already obtained about... more
The quantum eraser is a device that illustrates the quantum principle of complementarity and shows how a dephased system can regain its lost quantum behavior by erasing the "which-path" information already obtained about it. Thus far, quantum erasers were constructed predominantly in optical systems. Here, we present a realization of a quantum eraser in a mesoscopic electronic device. The use of interacting electrons, instead of noninteracting photons, allows control over the extracted information and a smooth variation of the degree of quantum erasure. The demonstrated system can serve as a first step toward a variety of more complex setups.
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Oscillations of the resistance observed under electromagnetic wave excitation in the high mobility GaAs/AlGaAs 2DES are examined as a function of the radiation frequency and the power, utilizing an empirical lineshape based on... more
Oscillations of the resistance observed under electromagnetic wave excitation in the high mobility GaAs/AlGaAs 2DES are examined as a function of the radiation frequency and the power, utilizing an empirical lineshape based on exponentially damped sinusoids. The fit-analysis indicates the resistance oscillation frequency, F, increases with the radiation frequency, n, at the rate dF/dn = 2.37 mTesla/GHz; the damping parameter, a, is approximately independent of n at constant power; and the amplitude, A, of the oscillations grows slowly with the incident power, at a constant temperature and frequency. The lineshape appears to provide a good description of the data.
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The exact structure of edge modes in "hole conjugate" fractional quantum Hall states remains an unsolved issue despite significant experimental and theoretical efforts devoted to their understanding. Recently, there has... more
The exact structure of edge modes in "hole conjugate" fractional quantum Hall states remains an unsolved issue despite significant experimental and theoretical efforts devoted to their understanding. Recently, there has been a surge of interest in such studies led by the search for neutral modes, which in some cases may lead to exotic statistical properties of the excitations. In this Letter, we report on detailed measurements of shot noise, produced by partitioning of the more familiar 2/3 state. We find a fractional charge of (2/3)e at the lowest temperature, decreasing to e/3 at an elevated temperature. Surprisingly, strong shot noise had been measured on a clear 1/3 plateau upon partitioning the 2/3 state. This behavior suggests an uncommon picture of the composite edge channels quite different from the accepted one.
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We observe microwave-induced photocurrent and photovoltage oscillations around zero as a function of the applied magnetic field in high mobility GaAs 2D electron systems. The photosignals pass zero whenever the microwave frequency is... more
We observe microwave-induced photocurrent and photovoltage oscillations around zero as a function of the applied magnetic field in high mobility GaAs 2D electron systems. The photosignals pass zero whenever the microwave frequency is close to a multiple of the cyclotron resonance frequency. They originate from built-in electric fields due to for instance band bending at contacts. The oscillations correspond to a suppression (screening) or an enhancement ("antiscreening") of these fields by the photoexcited electrons.
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We investigate the quantum Hall stripe phase at filling factor 9/2 at the microscopic level by probing the dispersion of its collective modes with the help of surface acoustic waves with wavelengths down to 60 nm. The dispersion is... more
We investigate the quantum Hall stripe phase at filling factor 9/2 at the microscopic level by probing the dispersion of its collective modes with the help of surface acoustic waves with wavelengths down to 60 nm. The dispersion is strongly anisotropic. It is highly dispersive and exhibits a roton minimum for wave vectors aligned along the easy transport direction. In the perpendicular direction, however, the dispersion is featureless, although not flat as predicted by theory. Oscillatory behavior in the absorption intensity of the collective mode with a wave vector perpendicular to the stripes is attributed to a commensurability effect. It allows us to extract the periodicity of the quantum Hall stripes.
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The energy spectrum of a two-dimensional electron system in a perpendicular homogeneous magnetic field and a weak lateral superlattice potential with square symmetry is composed of Landau bands with recursive internal subband structure.... more
The energy spectrum of a two-dimensional electron system in a perpendicular homogeneous magnetic field and a weak lateral superlattice potential with square symmetry is composed of Landau bands with recursive internal subband structure. The Hall conductance in the minigaps is anticipated to be quantized in integer multiples of e(2)/h that vary erratically from minigap to minigap in accordance with a Diophantine equation. Hall measurements on samples with the requisite properties uncover this long searched for evidence of Hofstadter's butterflylike energy spectrum.
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ABSTRACT
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We report transport and nuclear spin relaxation studies of a density tunable two-dimensional electron system at filling nu=1/2 in tilted magnetic fields. The transition from partial to full spin polarization with an in-plane field leaves... more
We report transport and nuclear spin relaxation studies of a density tunable two-dimensional electron system at filling nu=1/2 in tilted magnetic fields. The transition from partial to full spin polarization with an in-plane field leaves a clear signature in the resistance. Nuclear spin relaxation studies suggest that puddles of minority spins are responsible for an observed non-Korringa temperature dependence. This inhomogeneous spin polarization, similarly encountered in manganites where it strongly affects resistance, may help with understanding the spin dependent transport at nu=1/2.
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... 90, 026804 (2003). 19 T. Rejec and Y. Meir, Nature (London) 442, 900 (2006). 20 JH Hsiao, KM Liu, SY Hsu, and TM Hong, Phys. Rev. B 79, 033304 (2009). 21 F. Sfigakis, CJB Ford, M. Pepper, M. Kataoka, DA Ritchie, and MY Simmons, Phys.... more
... 90, 026804 (2003). 19 T. Rejec and Y. Meir, Nature (London) 442, 900 (2006). 20 JH Hsiao, KM Liu, SY Hsu, and TM Hong, Phys. Rev. B 79, 033304 (2009). 21 F. Sfigakis, CJB Ford, M. Pepper, M. Kataoka, DA Ritchie, and MY Simmons, Phys. Rev. Lett. 100, 026807 (2008). ...
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We investigate commensurability oscillations in the magnetoresistances of unstressed ungated rectangular two-dimensional superlattices of different periods. The amplitude of the commensurability oscillations in these systems exhibits a... more
We investigate commensurability oscillations in the magnetoresistances of unstressed ungated rectangular two-dimensional superlattices of different periods. The amplitude of the commensurability oscillations in these systems exhibits a nonmonotonic dependence on the applied magnetic field, which is not present in 1D or square superlattices. Furthermore, the high and low resistance directions switch between the two axial directions of the superlattices depending
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... where Vsd is the applied dc excitation voltage, gi=gi−gi−1, with gj = je2/h, t i−i−1 = g−gi−1 gi is the transmission probability of the ith channel, and g is the two-terminal ... We thank Ady Stern, Yuval Gefen, Bernd Rosenow, Dario... more
... where Vsd is the applied dc excitation voltage, gi=gi−gi−1, with gj = je2/h, t i−i−1 = g−gi−1 gi is the transmission probability of the ith channel, and g is the two-terminal ... We thank Ady Stern, Yuval Gefen, Bernd Rosenow, Dario Ferraro, and Maura Sassetti for helpful discussions. ...
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A density-tunable GaAs-AlGaAs heterostructure is used to study the density dependence of the filling factor nu=(5)/(2) and other fractional and reentrant integer quantum-Hall states in the second Landau level. The activation energy at... more
A density-tunable GaAs-AlGaAs heterostructure is used to study the density dependence of the filling factor nu=(5)/(2) and other fractional and reentrant integer quantum-Hall states in the second Landau level. The activation energy at nu=(5)/(2) can be determined for densities between 1.3 and 2.7×1011/cm2 and reaches up to 310 mK. The 5/2 energy gap is calculated numerically, including finite width and Landau-level-mixing corrections, both as a function of electron density. The discrepancy between theory and experiment increases moderately with density and reaches about 1.5 K at the highest density. We argue that the activation energy is strongly influenced by disorder from ionized donors and attribute this to the surprisingly large size of the 5/2 quasiparticles. We find that the quasiparticles have a diameter of at least 12 times the magnetic length or 150 nm at a magnetic field of 4 T. Implications for heterostructure design are discussed.
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... With electron beam lithography (EBL) and electrodeposition it is possible to generate ferromagnetic nanostructures with high aspect-ratio [1]. While the micromagnetic properties of the arrays are interesting on its own and can be... more
... With electron beam lithography (EBL) and electrodeposition it is possible to generate ferromagnetic nanostructures with high aspect-ratio [1]. While the micromagnetic properties of the arrays are interesting on its own and can be probed, eg by micro-Hall magnetometry [2], we ...