Publications (45)104.13 Total impact
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ABSTRACT: The dependence of the quasiparticle Fermi energy on the electron density is investigated by analyzing the radiative recombination spectra of twodimensional electrons with photoexcited holes bound at remote acceptors. In this way, the electrondensity dependence of the renormalized mass of quasiparticles is determined. It is established that, as the electron density decreases (the parameter r s increases to 4.5), the densityofstates effective mass of quasiparticles increases by 35% as compared to the cyclotron mass of the electron. It is shown that, in a perpendicular magnetic field, the concept of quasiparticles in a twodimensional Fermi liquid is applicable not only near the Fermi level but also deeply below the Fermi surface, even to the bottom of the quantumconfinement subband, because the broadening of excitations remains considerably smaller than their energy.  [Show abstract] [Hide abstract]
ABSTRACT: We study single quantum wells and matched density bilayer samples. Simultaneous measurements of the Hall voltages using low frequency lockin techniques and of the changes in the 232 MHz (12.6 μm) SAW propagation measured with a vector networkanalyzer allow comparison of the complex bulk and edge conductivities. The vtotal = 1 bilayer state is seen directly in the SAW measurement only when the conductivity is below ~ 6 × 107 Siemens and is destroyed at moderate SAW powers by localized heating. The simultaneous reduction of the conductivity minima extracted from Hall data and from SAW data conclusively demonstrates that the vtotal = 1 state disappears simultaneously throughout the bulk and not by the formation of competing domains or conducting filaments. 
Article: Local compressibility measurement of the νtot=1 quantum Hall state in a bilayer electron system
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ABSTRACT: The filling νtot=1 quantum Hall state under charge imbalance is investigated through both transport and thermodynamic measurements on a highmobility lowdensity GaAs bilayer sample with negligible single particle tunneling. The νtot=1 state demonstrates its robustness against imbalance by evolving continuously from the single layer regime (νupper=1, νlower=0) to the bilayer regime with fillings νupper=1/3 and νlower=2/3 for the separate layers. The energy gap of the νtot=1 state obtained from compressibility measurements using single electron transistors depends on position, i.e., the local disorder potential. Nevertheless, compressibility and thermal activation measurements yield comparable values for the energy gap under imbalance. 
Article: Lighthole quantization in the optical response of ultrawide GaAs/AlxGa1xAs quantum wells
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ABSTRACT: Temperaturedependent reflectivity and photoluminescence spectra are studied for undoped ultrawide 150 nm and 250 nm GaAs quantum wells. It is shown that spectral features previously attributed to a size quantization of exciton motion in zdirection coincide well with energies of quantized levels for light holes. Furthermore, optical spectra reveal very similar properties at temperatures above exciton dissociation point. 
Article: Resonant Rayleigh scattering as a probe of spin polarization in a twodimensional electron system
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ABSTRACT: We investigated the resonant Rayleigh scattering in a twodimensional electron system (2DES) and developed a differential technique for obtaining highquality RRS spectra. Oscillations of the RRS scattering efficiency are observed. The oscillations are explained in terms of redistribution of electron spins within two spin subbands of the zero Landau level. The RRS serves as an effective probe of the electron spin polarization in the ground state of 2DES. 
Article: Critical tunnel currents and dissipation of QuantumHall bilayers in the excitonic condensate state
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ABSTRACT: Transport and tunneling is studied in the regime of the excitonic condensate at total filling factor one using the counterflow geometry. At small currents the coupling between the layers is large making the two layers virtually electrically inseparable. Above a critical current the tunneling becomes negligible. An onset of dissipation in the longitudinal transport is observed in the same current range. 
Article: Electron gfactor anisotropy in GaAs/Al_ {1− x} Ga_ {x} As quantum wells of different symmetry
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ABSTRACT: The anisotropy of the electron g factor is investigated in symmetrically (SQW) and asymmetrically (AQW) doped 20nm GaAs/AlGaAs quantum wells, grown in the [001] direction. Applied was the electrically detected electron spin resonance technique. The AQW demonstrates strong twofold inplane gfactor anisotropy with the [110] and [11̅ 0] principal axes. This can be readily ascribed to the internal electric field asymmetry as caused by singleside doping. The SQW is shown to have 10 times as weak (but still detectable) anisotropy with the same principal axes. The linear (in the magnetic field) corrections to the g factor were also carefully measured. The â tensor of these corrections is shown to have at least three different nonzero components, namely, azzz, axxz, and ayyz.  [Show abstract] [Hide abstract]
ABSTRACT: The luminescence spectra due to recombination of twodimensional electrons with optically excited holes have been studied in a wide range of electron filling factors in the transverse magnetic field. A nonmonotonic fillingfactor dependence of the energy splitting between different circular polarizations of photoluminescence from the completely filled zeroth Landau level of electrons has been observed. It has been shown that this dependence is associated with collective (excitonic) effects that appear due to the interaction between electrons from partially occupied upper Landau levels and holes remaining on the zeroth Landau level after recombination.  [Show abstract] [Hide abstract]
ABSTRACT: An electron bilayer system is realized in a wide GaAs quantum well. The chemical potentials of both layers can be tuned by intrinsic back and top gates. The Landau level spectrum for various charge distributions is probed by photoluminescence (PL), able to discriminate between both layers independently. The PL spectra show unambiguously how the system spontaneously deforms itself in strong magnetic fields as a consequence of energy minimization under Landau quantization and huge SAS energy gaps, reaching up to the cyclotron energy, become visible in the PL spectra [1]. [4pt] [1] V.V. Solovyev, S. Schmult, W. Dietsche, I.V. Kukushkin, PRB 80, 241310, 2009.  [Show abstract] [Hide abstract]
ABSTRACT: A prerequisite towards BoseEinstein condensation is a cold and dense system of bosons. Indirect excitons in double GaAs/AlGaAs quantum wells (DQWs) are believed to be suitable candidates. Indirect excitons are formed in asymmetric DQW structures by mass filtering, a method which does not require external electric fields. The exciton density and the electronhole balance can be tuned optically. Binding energies are measured by a resonant microwave absorption technique. Our results show that screening of the indirect excitons becomes already relevant at densities as low as 5x10^9cm2 and results in their destruction.  [Show abstract] [Hide abstract]
ABSTRACT: In this paper, the highfrequency ($f=0.05$\char21{}10 GHz) magnetoresistance of a twodimensional electron system is studied in the regime of microwaveinduced resistance oscillations (MIRO). For this purpose, we employed a technique based on measuring the attenuation of a broadband coplanar transmission line placed on the sample surface, with the sample simultaneously being subjected to external microwave irradiation of frequency $F=40$\char21{}140 GHz. In the $f$\leqslant${}1$ GHz probe frequency range, the coplanar waveguide transmission exhibits several features that repeat the MIRO measured on the same sample using the conventional dc transport technique. At higher probe signal frequencies $f$, the MIRO features in transmission are significantly suppressed. In particular, for a microwave irradiation frequency of $F=80$ GHz, the first two features of the waveguide transmission decrease by an order of magnitude at ${f}_{1}=3.0$ GHz and ${f}_{2}=1.5$ GHz, respectively. 
Article: Observation of hybrid plasmonphoton modes in microwave transmission of coplanar microresonators
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ABSTRACT: Microwave transmission of a coplanar microresonator deposited on a sample surface over a twodimensional electron system has been studied. The transmission signal reveals a series of resonances corresponding to the excitation of hybrid cavity plasmonphoton modes, and ultrastrong plasmonphoton coupling has been realized. The hybridization frequency (Rabi frequency) is shown to be anomalously larger than the frequencies of unperturbed modes and it reaches values of up to $25$ GHz. The effect of electron density and magnetic field on the excitation spectrum of cavity polariton has been investigated.  [Show abstract] [Hide abstract]
ABSTRACT: The anisotropy of electron gfactor is investigated for several GaAs/AlxGa1xAs heterostructures using an electrically detected electron spin resonance technique at liquid helium temperature. For a modulationdoped 25nm single quantum well with electron density n=4×1011 cm2 we extracted an outofplane gfactor value of gzz=0.410 and inplane values of gyy=0.359 and gxx=0.289. In addition, linear in magnetic field corrections to the gfactor components were also extracted and strong anisotropy in their values was established.  [Show abstract] [Hide abstract]
ABSTRACT: A new method of creating indirect excitons in asymmetric double quantum wells, based on mass filtering, is introduced in this paper. It is shown that different tunneling times of electrons and holes from the narrow well to the wide one in connection with fine tuning of the carrier density by a small barrier photoexcitation allow the creation of an electrically neutral system of indirect excitons. Resonant microwave absorption is investigated in such a doublelayer system which detects both sizedependent plasma resonances for the case of a charged electronhole system and sizeindependent indirect exciton 1S2S transitions in the case of a neutral system. The exciton transition energy is measured as a function of the layer separation, and a contradiction with theoretical predictions is established which indicates a strong dielectric screening of excitonic states due to overlap of their wavefunctions.  [Show abstract] [Hide abstract]
ABSTRACT: We report the observation of inverse magnetic field periodic, radiationinduced magnetoresistance oscillations in GaAs/AlGaAs heterostructures prepared in W. Wegscheider’s group, compare their characteristics with similar oscillations in V. Umansky’s material, and describe the lineshape variation vs the radiation power, P, in the two systems. We find that the radiationinduced oscillatory resistance, ΔRxx, in both materials, can be described by ΔRxx=−A exp(−λ/B)sin(2πF/B), where A is the amplitude, λ is the damping parameter, and F is the oscillation frequency. Both λ and F turn out to be insensitive to P. On the other hand, A grows nonlinearly with P.  [Show abstract] [Hide abstract]
ABSTRACT: Utilizing an intrinsically densitymatched double quantum well system, a twoterminal resistance of the strongly correlated total filling factor one (nu(tot)=1) state measuring h/e(2) is determined. In contrast to conventional devices exhibiting the nu(tot)=1 state exclusively in regions, where the densities are adjusted by biasing front and back gate electrodes, the intrinsic devices show the nu(tot)=1 state without any external control. Moreover, the intrinsically densitymatched systems allow for direct contacting of the nu(tot)=1 quantum Hall edges. Transport measurements indicate that under the nu(tot)=1 condition, both layers become indistinguishable. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3319260]  [Show abstract] [Hide abstract]
ABSTRACT: We report on the observation of a new spin mode in a quantum Hall system in the vicinity of odd electron filling factors under experimental conditions excluding the possibility of Skyrmion excitations. The new mode having presumably zero energy at odd filling factors emerges at small deviations from odd filling factors and couples to the spinexciton. The existence of an extra spin mode assumes a nontrivial magnetic order at partial fillings of Landau levels surrounding quantum Hall ferromagnets other then the Skyrmion crystal. 
Article: Interlayer Tunneling in Counterflow Experiments on the Excitonic Condensate in Quantum Hall Bilayers
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ABSTRACT: The effect of tunneling on the transport properties of} quantum Hall double layers in the regime of the excitonic condensate at total filling factor one is studied in counterflow experiments. If the tunnel current $I$ is smaller than a critical $I_C$, tunneling is large and is effectively shorting the two layers. For $I > I_C$ tunneling becomes negligible. Surprisingly, the transition between the two tunneling regimes has only a minor impact on the features of the fillingfactor one state as observed in magnetotransport, but at currents exceeding $I_C$ the resistance along the layers increases rapidly. 
Article: Nonlinear growth with the microwave intensity in radiationinduced magnetoresistance oscillations
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ABSTRACT: We compare the characteristics of inversemagneticfield periodic, radiationinduced magnetoresistance oscillations in GaAs/AlGaAs heterostructures prepared by W. Wegscheider et al., and V. Umansky, by fitting the observed lineshape vs. the radiation power, P, in the two MBE materials. We find that the radiationinduced oscillatory δRxx, in both materials, can be described by δRxx= A exp(λ/B)sin(2 πF/B), where A is the amplitude, λ is the damping parameter, and F is the oscillation frequency. Both λ and F turn out to be insensitive to P. On the other hand, A grows nonlinearly with P.  [Show abstract] [Hide abstract]
ABSTRACT: We study magnetotransport in the quantum Hall (QH) regime of a twodimensional electron system with an epitaxially overgrown sharp cleavededge. A thick insulating barrier is overgrown at the cleavededge followed by a doped layer, serving as a side gate which can control depletion or accumulation at the sharp edge, hence can convert a sharp edge into a soft edge by changing the gate bias. This geometry leads to a tunable edge potential with either the standard incompressible strips in the ``soft edge'' limit, or thin or vanishing incompressible strips in the ``sharp edge'' limit. DC magnetotransport measurements show evidence of a longitudinal resistance minimum whose width depends on the current direction. This experimental result is consistent with recent theory on the role of edge potentials in defining the QH in small samples [1]. Size effect and gate bias dependence are studied. We also report an unexplained magnetic field hysteresis at the high field side of filling factors nu=1, 2, 3, 4 in the limit of negative sidegate bias.[4pt] [1] A. Siddiki, Euro. Phys. Lett. 87, 17008(2009)
Publication Stats
369  Citations  
104.13  Total Impact Points  
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Institutions

2013

Technische Universität Dresden
Dresden, Saxony, Germany


20082013

Max Planck Institute for Solid State Research
Stuttgart, BadenWürttemberg, Germany


20022010

Universität Regensburg
 Institut für Experimentelle und Angewandte Physik
Regensburg, Bavaria, Germany


2009

Russian Academy of Sciences
 Institute of Solid State Physics
Moscow, Moscow, Russia
