Publications (33)130.1 Total impact

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ABSTRACT: A threeterminal device based upon a twodimensional electron system is investigated in the regime of nonequilibrium transport. Excited electrons scatter with the cold Fermi sea and transfer energy and momentum to other electrons. A geometry analogous to a water jet pump is used to create a jet pump for electrons. Because of its phenomenological similarity we name the observed behavior the “electronic Venturi effect.”Journal of Applied Physics 06/2011; DOI:10.1063/1.3577959 · 2.19 Impact Factor 
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ABSTRACT: The energy relaxation channels of hot electrons far from thermal equilibrium in a degenerate twodimensional electron system are investigated in transport experiments in a mesoscopic threeterminal device. We observe a transition from two dimensions at zero magnetic field to quasionedimensional scattering of the hot electrons in a strong magnetic field. In the twodimensional case electronelectron scattering is the dominant relaxation mechanism, while the emission of optical phonons becomes more and more important as the magnetic field is increased. The observation of up to 11 optical phonons emitted per hot electron allows us to determine the onset energy of LO phonons in GaAs at cryogenic temperatures with a high precision, $\eph=36.0\pm0.1\,$meV. Numerical calculations of electronelectron scattering and the emission of optical phonons underline our interpretation in terms of a transition to onedimensional dynamics.Physical review. B, Condensed matter 04/2011; 83. DOI:10.1103/PhysRevB.83.235404 · 3.66 Impact Factor 
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ABSTRACT: We explore the acoustic phononbased interaction between two neighboring coplanar circuits containing semiconductor quantum point contacts in a perpendicular magnetic field B. In a dragtype experiment, a current flowing in one of the circuits (unbiased) is measured in response to an external current in the other. In moderate B the sign of the induced current is determined solely by the polarity of B. This indicates that the spatial regions where the phonon emission/reabsorption is efficient are controlled by magnetic field. The results are interpreted in terms of nonequilibrium transport via skipping orbits in twodimensional electron system.Physical review. B, Condensed matter 08/2010; DOI:10.1103/PhysRevB.82.201310 · 3.66 Impact Factor 
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ABSTRACT: Time resolved electronic dynamics in coupled quantum dots is directly obtained by a pulsedgate technique. While individual gate voltages are modulated with periodic pulse trains average charge occupations are measured. A nearby quantum point contact serves as detector. A key component of our setup is a radio frequency sample holder based on impedance matched micro strip lines virtually free of crosstalk. It allows to observe displacements of single electrons on time scales well below a nanosecond. Microscopically resolved tunneling rates as well as relaxation times are obtained by using an adapted rate equation model.Physical review. B, Condensed matter 06/2010; DOI:10.1103/PhysRevB.82.195310 · 3.66 Impact Factor 
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ABSTRACT: Quantum point contacts (QPCs) are commonly employed to detect capacitively the charge state of coupled quantum dots (QDs). An indirect backaction of a biased QPC onto a double QD laterally defined in a GaAs/AlGaAs heterostructure is observed. Energy is emitted by nonequilibrium charge carriers in the leads of the biased QPC. Part of this energy is absorbed by the double QD where it causes charge fluctuations that can be observed under certain conditions in its stability diagram. By investigating the spectrum of the absorbed energy, we find that both acoustic phonons and Coulomb interaction can be involved in the backaction, depending on the geometry and coupling constants.Physical Review Letters 05/2010; 104(19):196801. DOI:10.1103/PhysRevLett.104.196801 · 7.73 Impact Factor 
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ABSTRACT: We investigate an electronic MachZehnder interferometer with high visibility in the quantum Hall regime. The superposition of the electrostatic potentials from a quantum point contact (QPC) and the residual disorder potential from doping impurities frequently results in the formation of inadvertent quantum dots (QDs) in one arm of the interferometer. This gives rise to resonances in the QPC transmission characteristics. While crossing the QD resonance in energy, the interferometer gains a phase shift of π in the interference pattern.Physical review. B, Condensed matter 05/2010; 81(20). DOI:10.1103/PhysRevB.81.205425 · 3.66 Impact Factor 
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ABSTRACT: Scattering of otherwise ballistic electrons far from equilibrium is investigated in a cold twodimensional electron system. The interaction between excited electrons and the degenerate Fermi liquid induces a positive charge in a nanoscale region which would be negatively charged for diffusive transport at local thermal equilibrium. In a threeterminal device we observe avalanche amplification of electrical current, resulting in a situation comparable to the Venturi effect in hydrodynamics. Numerical calculations using a random phase approximation are in agreement with our data and suggest Coulomb interaction as the dominant scattering mechanism. Comment: 4 pages, 4 figuresPhysical review. B, Condensed matter 01/2010; DOI:10.1103/PhysRevB.82.161416 · 3.66 Impact Factor 
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ABSTRACT: We investigate an electronic MachZehnder interferometer with high visibility in the quantum Hall regime. The superposition of the electrostatic potentials from a quantum point contact (QPC) and the residual disorder potential from doping impurities frequently results in the formation of inadvertent quantum dots (QD) in one arm of the interferometer. This gives rise to resonances in the QPC transmission characteristics. While crossing the QD resonance in energy, the interferometer gains a phase shift of $\pi$ in the interference pattern. Comment: 5 pages, 4 figures 
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ABSTRACT: Interactions between mesoscopic devices induced by interface acoustic phonons propagating in the plane of a twodimensional electron system (2DES) are investigated by phonon spectroscopy. In our experiments, ballistic electrons injected from a biased quantum point contact emit phonons and a portion of them are reabsorbed exciting electrons in a nearby degenerate 2DES. We perform energy spectroscopy on these excited electrons employing a tunable electrostatic barrier in an electrically separate and unbiased detector circuit. The transferred energy is found to be bounded by a maximum value corresponding to Fermilevel electrons excited and backscattered by absorbing interface phonons. Our results imply that phononmediated interaction plays an important role for the decoherence of solidstatebased quantum circuits.Physical Review Letters 06/2009; 102(18):186801. DOI:10.1103/PhysRevLett.102.186801 · 7.73 Impact Factor 
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ABSTRACT: We briefly overview our recent results on nonequilibrium interactions between neighboring electrically isolated nanostructures. One of the nanostructures is represented by an externally biased quantum point contact (driveQPC), which is used to supply energy quanta to the second nanostructure (detector). Absorption of these nonequilibrium quanta of energy generates a dccurrent in the detector, or changes its differential conductance. We present results for a double quantum dot, a single quantum dot or a second QPC placed in the detector circuit. In all three cases a detection of quanta with energies up to ~1 meV is possible for bias voltages across the driveQPC in the mV range. The results are qualitatively consistent with an energy transfer mechanism based on nonequilibrium acoustic phonons.Journal of Physics Condensed Matter 06/2008; DOI:10.1088/09538984/20/45/454205 · 2.22 Impact Factor 
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ABSTRACT: We report on nonequilibrium interaction phenomena between adjacent but electrostatically separated nanostructures in GaAs. A current flowing in one externally biased nanostructure causes an excitation of electrons in a circuit of a second nanostructure. As a result we observe a dc current generated in the unbiased second nanostructure. The results can be qualitatively explained in terms of acoustic phonon based energy transfer between the two mutually isolated circuits.Physica E Lowdimensional Systems and Nanostructures 06/2008; 40(540):995998. DOI:10.1016/j.physe.2007.08.107 · 1.86 Impact Factor 
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ABSTRACT: We study the visibility of AharonovBohm interference in an electronic MachZehnder interferometer (MZI) in the integer quantum Hall regime. The visibility is controlled by the filling factor $\nu$ and is observed only between $\nu \approx 2.0$ and 1.0, with an unexpected maximum near $\nu=1.5$. Three energy scales extracted from the temperature and voltage dependences of the visibility change in a very similar way with the filling factor, indicating that the different aspects of the interference depend sensitively on the local structure of the compressible and incompressible strips forming the quantum Hall edge channels.Physical review. B, Condensed matter 03/2008; 78(7). DOI:10.1103/PhysRevB.78.075303 · 3.66 Impact Factor 
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ABSTRACT: We study an electronic MachZehnder interferometer employing the edge channels of a twodimensional electron gas (2DEG) in the quantum Hall regime and quantum point contacts (QPC) as beam splitters. The linear conductance of the QPC as a function of gate voltage shows resonances superimposed on quantized conductance steps. It was found that the visibility depends strongly on magnetic field and is highest near a filling factor of 1.5 in the interferometer arm. (c) 2007 Elsevier B.V. All rights reserved.Physica E Lowdimensional Systems and Nanostructures 03/2008; DOI:10.1016/j.physe.2007.10.060 · 1.86 Impact Factor 
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ABSTRACT: We study the interaction between two adjacent but electrically isolated quantum point contacts (QPCs). At high enough sourcedrain bias on one QPC, the drive QPC, we detect a finite electric current in the second, unbiased, detector QPC. The current generated at the detector QPC always flows in the opposite direction than the current of the drive QPC. The generated current is maximal, if the detector QPC is tuned to a transition region between its quantized conductance plateaus and the drive QPC is almost pinchedoff. We interpret this counterflow phenomenon in terms of an asymmetric phononinduced excitation of electrons in the leads of the detector QPC.Physical Review Letters 09/2007; 99(9):096803. DOI:10.1103/PhysRevLett.99.096803 · 7.73 Impact Factor 
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ABSTRACT: We observe an experimental signature of the role of phonons in spin relaxation between triplet and singlet states in a twoelectron quantum dot. Using both the external magnetic field and the electrostatic confinement potential, we change the singlettriplet energy splitting from 1.3 meV to zero and observe that the spin relaxation time depends nonmonotonously on the energy splitting. A simple theoretical model is derived to capture the underlying physical mechanism. The present experiment confirms that spinflip energy is dissipated in the phonon bath.Physical Review Letters 04/2007; 98(12):126601. DOI:10.1103/PhysRevLett.98.126601 · 7.73 Impact Factor 
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ABSTRACT: We demonstrate experimentally a readout method that distinguishes between twoelectron spin states in a quantum dot. This scheme combines the advantages of the two existing mechanisms for spintocharge conversion with singleshot charge detection: a large difference in energy between the two states and a large difference in tunnel rate between the states and a reservoir. As a result, a spin measurement fidelity of 97% was achieved, which is much higher than previously reported fidelities. 
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ABSTRACT: We demonstrate experimentally a readout method that distinguishes between twoelectron spin states in a quantum dot. This scheme combines the advantages of the two existing mechanisms for spintocharge conversion with singleshot charge detection: a large difference in energy between the two states and a large difference in tunnel rate between the states and a reservoir. As a result, a spin measurement fidelity of 97% was achieved, which is much higher than previously reported fidelities. (© 2006 WILEYVCH Verlag GmbH & Co. KGaA, Weinheim)physica status solidi (b) 12/2006; 243(15):3855  3858. DOI:10.1002/pssb.200671503 · 1.61 Impact Factor 
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ABSTRACT: We propose and implement a nondestructive measurement that distinguishes between twoelectron spin states in a quantum dot. In contrast to earlier experiments with quantum dots, the spins are left behind in the state corresponding to the measurement outcome. By measuring the spin states twice within a time shorter than the relaxation time T1, correlations between the outcomes of consecutive measurements are observed. They disappear as the wait time between measurements becomes comparable to T1. The correlation between the postmeasurement state and the measurement outcome is measured to be ∼90% on average.Physical Review B 11/2006; 74(19). DOI:10.1103/PhysRevB.74.195303 · 3.66 Impact Factor 
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ABSTRACT: We study a double quantum dot (DQD) coupled to a strongly biased quantum point contact (QPC), each embedded in independent electric circuits. For weak interdot tunneling we observe a finite current flowing through the Coulomb blockaded DQD in response to a strong bias on the QPC. The direction of the current through the DQD is determined by the relative detuning of the energy levels of the two quantum dots. The results are interpreted in terms of a quantum ratchet phenomenon in a DQD energized by a nearby QPC.Physical Review Letters 11/2006; 97(17):176803. DOI:10.1103/PhysRevLett.97.176803 · 7.73 Impact Factor 
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ABSTRACT: The activation gap Delta of the fractional quantum Hall state at constant filling nu=1/3 is measured in a wide range of perpendicular magnetic field B . Despite the full spin polarization of the incompressible ground state, we observe a sharp crossover between a lowfield linear dependence of Delta on B and a Coulomblike square root behavior at large B . From the global gap reduction we get information about the mobility edges in the fractional quantum Hall regime.Physical Review B 10/2006; 74. DOI:10.1103/PhysRevB.74.165325 · 3.66 Impact Factor
Publication Stats
820  Citations  
130.10  Total Impact Points  
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Institutions

2004–2011

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


2008

LudwigMaximilianUniversity of Munich
 Center for Nanoscience (CeNS)
München, Bavaria, Germany


2007

University Hospital Regensburg
Ratisbon, Bavaria, Germany
