Publications (44)102.61 Total impact
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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.Journal of Physics Conference Series 08/2013; 456(1):2030. 
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.Physical review. B, Condensed matter 05/2013; 87(20). · 3.66 Impact Factor 
Article: Lighthole quantization in the optical response of ultrawide GaAs/Al(x)Ga(1x)As quantum wells.
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ABSTRACT: Temperaturedependent reflectivity and photoluminescence spectra are studied for undoped ultrawide 150 and 250 nm GaAs quantum wells. It is shown that spectral features previously attributed to a size quantization of the exciton motion in the zdirection coincide well with energies of quantized levels for light holes. Furthermore, optical spectra reveal very similar properties at temperatures above the exciton dissociation point.Journal of Physics Condensed Matter 11/2012; 25(2):025801. · 2.22 Impact Factor 
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.Physical review. B, Condensed matter 03/2012; 85(11). · 3.66 Impact Factor 
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.Journal of Physics Conference Series 12/2011; 334(1):012024. 
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.Physical review. B, Condensed matter 12/2011; 84(23). · 3.66 Impact Factor  [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, 2009.03/2011;  [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.03/2011;  [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.JETP Letters 01/2011; 92(9):600606. · 1.52 Impact Factor  Physical Review B. 01/2011; 83:14.

Article: Observation of hybrid plasmonphoton modes in microwave transmission of coplanar microresonators
Physical Review B. 01/2011; 83:15. 
Article: gfactor anisotropy in a GaAs/Al_ {x} Ga_ {1x} As quantum well probed by electron spin resonance
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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.Physical review. B, Condensed matter 01/2011; 83(4). · 3.66 Impact Factor  [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.Semiconductor Science and Technology 01/2011; 26(1). · 1.92 Impact Factor  [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.Physical review. B, Condensed matter 11/2010; 81(12). · 3.66 Impact Factor  [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 spin exciton. 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.Physical Review Letters 04/2010; 104(13):136804. · 7.73 Impact Factor  [Show abstract] [Hide abstract]
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.03/2010;  [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)03/2010;  [Show abstract] [Hide abstract]
ABSTRACT: The effect of tunneling on the transport properties of quantum Hall double layers in the regime of the excitonic condensate at a 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.Physical Review Letters 03/2010; 104(11):116802. · 7.73 Impact Factor  Journal of Vacuum Science & Technology B  J VAC SCI TECHNOL B. 01/2010; 28(3).
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ABSTRACT: Photoluminescence studies of a wide asymmetric quantum well hosting two strongly coupled electron layers demonstrate unambiguously how such a system deforms itself due to interlayer charge transfer in a quantizing magnetic field thus manifesting its overall singlelayer appearance. The charge distribution inside the quantum well is balanced for total filling factor ν=4N (N integer), while it is imbalanced at most for ν=4N+2. The intersubband energy oscillates enormously with the applied magnetic field and reaches values as large as the electron cyclotron energy for filling factors 4N.Physical review. B, Condensed matter 12/2009; 80(24). · 3.66 Impact Factor
Publication Stats
184  Citations  
102.61  Total Impact Points  
Top Journals
Institutions

2008–2013

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


2009–2010

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


2002–2010

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


2003

Ioffe Physical Technical Institute
 Centre of Nanoheterostructure Physics
SanktPeterburg, St.Petersburg, Russia
