S. Schmult

Max Planck Institute for Solid State Research, Stuttgart, Baden-Württemberg, Germany

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Publications (45)104.13 Total impact

  • I. V. Kukushkin · S. Schmult
    JETP Letters 05/2015; 101(10):693-698. DOI:10.1134/S0021364015100082 · 1.36 Impact Factor
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    ABSTRACT: We study single quantum wells and matched density bilayer samples. Simultaneous measurements of the Hall voltages using low frequency lock-in techniques and of the changes in the 232 MHz (12.6 μm) SAW propagation measured with a vector network-analyzer 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 × 10-7 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-. DOI:10.1088/1742-6596/456/1/012030
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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 high-mobility low-density 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). DOI:10.1103/PhysRevB.87.205304 · 3.66 Impact Factor
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    ABSTRACT: Temperature-dependent reflectivity and photoluminescence spectra are studied for undoped ultra-wide 150 nm and 250 nm GaAs quantum wells. It is shown that spectral features previously attributed to a size quantization of exciton motion in z-direction coincide well with energies of quantized levels for light holes. Furthermore, optical spectra reveal very similar properties at temperatures above exciton dissociation point.
    Journal of Physics Condensed Matter 11/2012; 25(2):025801. DOI:10.1088/0953-8984/25/2/025801 · 2.35 Impact Factor
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    ABSTRACT: We investigated the resonant Rayleigh scattering in a two-dimensional electron system (2DES) and developed a differential technique for obtaining high-quality 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). DOI:10.1103/PhysRevB.85.113403 · 3.66 Impact Factor
  • Y Yoon · X Huang · E Yarar · W Dietsche · L Tiemann · S Schmult · K v Klitzing
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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. DOI:10.1088/1742-6596/334/1/012024
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    ABSTRACT: The anisotropy of the electron g factor is investigated in symmetrically (SQW) and asymmetrically (AQW) doped 20-nm GaAs/AlGaAs quantum wells, grown in the [001] direction. Applied was the electrically detected electron spin resonance technique. The AQW demonstrates strong twofold in-plane g-factor anisotropy with the [110] and [11̅ 0] principal axes. This can be readily ascribed to the internal electric field asymmetry as caused by single-side 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). DOI:10.1103/PhysRevB.84.233302 · 3.66 Impact Factor
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    ABSTRACT: The luminescence spectra due to recombination of two-dimensional electrons with optically excited holes have been studied in a wide range of electron filling factors in the transverse magnetic field. A nonmonotonic filling-factor 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 11/2011; 92(9):600-606. DOI:10.1134/S0021364010210071 · 1.36 Impact Factor
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    ABSTRACT: A prerequisite towards Bose-Einstein 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 electron-hole 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 5x10^9cm-2 and results in their destruction.
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    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.
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    ABSTRACT: In this paper, the high-frequency ($f=0.05$\char21{}10 GHz) magnetoresistance of a two-dimensional electron system is studied in the regime of microwave-induced 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.
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    ABSTRACT: Microwave transmission of a coplanar microresonator deposited on a sample surface over a two-dimensional electron system has been studied. The transmission signal reveals a series of resonances corresponding to the excitation of hybrid cavity plasmon-photon modes, and ultrastrong plasmon-photon 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.
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    ABSTRACT: The anisotropy of electron g-factor is investigated for several GaAs/AlxGa1-xAs heterostructures using an electrically detected electron spin resonance technique at liquid helium temperature. For a modulation-doped 25-nm single quantum well with electron density n=4×1011 cm-2 we extracted an out-of-plane g-factor value of |gzz|=0.410 and in-plane values of |gyy|=0.359 and |gxx|=0.289. In addition, linear in magnetic field corrections to the g-factor components were also extracted and strong anisotropy in their values was established.
    Physical review. B, Condensed matter 01/2011; 83(4). DOI:10.1103/PhysRevB.83.041307 · 3.66 Impact Factor
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    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 double-layer system which detects both size-dependent plasma resonances for the case of a charged electron-hole system and size-independent indirect exciton 1S-2S 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). DOI:10.1088/0268-1242/26/1/014023 · 2.19 Impact Factor
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    R. G. Mani · C. Gerl · S. Schmult · W. Wegscheider · V. Umansky
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    ABSTRACT: We report the observation of inverse magnetic field periodic, radiation-induced 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 radiation-induced 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). DOI:10.1103/PhysRevB.81.125320 · 3.66 Impact Factor
  • S. Schmult · L. Tiemann · W. Dietsche · K. von Klitzing
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    ABSTRACT: Utilizing an intrinsically density-matched double quantum well system, a two-terminal 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 density-matched 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]
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 05/2010; 28(3). DOI:10.1116/1.3319260 · 1.46 Impact Factor
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    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. DOI:10.1103/PhysRevLett.104.136804 · 7.51 Impact Factor
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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 filling-factor one state as observed in magneto-transport, but at currents exceeding $I_C$ the resistance along the layers increases rapidly.
    Physical Review Letters 03/2010; 104(11):116802. DOI:10.1103/PhysRevLett.104.116802 · 7.51 Impact Factor
  • R. G. Mani · C. Gerl · S. Schmult · W. Wegscheider · V. Umansky
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    ABSTRACT: We compare the characteristics of inverse-magnetic-field- periodic, radiation-induced 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 radiation-induced 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.
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    ABSTRACT: We study magnetotransport in the quantum Hall (QH) regime of a two-dimensional electron system with an epitaxially overgrown sharp cleaved-edge. A thick insulating barrier is overgrown at the cleaved-edge 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 side-gate bias.[4pt] [1] A. Siddiki, Euro. Phys. Lett. 87, 17008(2009)

Publication Stats

296 Citations
104.13 Total Impact Points


  • 2008–2013
    • Max Planck Institute for Solid State Research
      Stuttgart, Baden-Württemberg, Germany
  • 2002–2010
    • Universität Regensburg
      • Institut für Experimentelle und Angewandte Physik
      Regensburg, Bavaria, Germany
  • 2009
    • Russian Academy of Sciences
      • Institute of Solid State Physics
      Moscow, Moscow, Russia