Werner Wegscheider

Last Name

Wegscheider

First Name

Werner

ORCID

0000-0002-2138-5558

Organisational unit

03833 - Wegscheider, Werner / Wegscheider, Werner

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Publications 1 - 10 of 97

Interlayer Tunneling in Counterflow Experiments on the Excitonic Condensate in Quantum Hall Bilayers
Yoon, Y.; Tiemann, Lars; Schmult, Stefan; et al. (2010)
Physical Review Letters
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 IC, tunneling is large and is effectively shorting the two layers. For I>IC 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 magnetotransport, but at currents exceeding IC the resistance along the layers increases rapidly. © 2010 The American Physical Society.
Capacitance and conductance oscillations from electron tunneling into high energy levels of a quantum well in a p-i-n diode
Parolo, Simon; Lupatini, Mirko; Külah, Elçin; et al. (2022)
Physical Review B
Two-dimensional electron and hole gases separated by a few nm from each other are produced in p-i-n diodes based upon molecular beam epitaxy-grown GaAs/AlGaAs heterostructures. At such interlayer distances, the exciton formation and possibly Bose-Einstein condensation (BEC) is expected. We measure the capacitance between the layers and find it to oscillate as a function of the bias voltage. The peak values exceed the geometric capacitance by up to a factor of 2. The surprisingly regular periods of the oscillations are of the order of 10 to 30 mV and scale linearly with the inverse of the thickness, between 60 and 150 nm, of the GaAs layer placed between the barrier and the p-doped AlGaAs. The oscillations are related to the resonant electron tunneling into high energy levels of this GaAs layer acting as a quantum well. We suggest that long lifetimes of the electrons in these levels are the origin of the large peak values of the capacitance. The possible relation of the capacitance oscillations with BEC is discussed.
Modifying the integer quantum Hall effect with cavity vacuum fields
Enkner, Josefine Ulrike; Appugliese, Felice; Paravicini-Bagliani, Gian L.; et al. (2022)
Measurements of Phase Dynamics in Planar Josephson Junctions and SQUIDs
Haxell, Daniel Z.; Cheah, Erik; Křížek, Filip; et al. (2023)
Physical Review Letters
We experimentally investigate the stochastic phase dynamics of planar Josephson junctions (JJs) and superconducting quantum interference devices (SQUIDs) defined in epitaxial InAs/Al heterostructures, and characterized by a large ratio of Josephson energy to charging energy. We observe a crossover from a regime of macroscopic quantum tunneling to one of phase diffusion as a function of temperature, where the transition temperature T∗ is gate-tunable. The switching probability distributions are shown to be consistent with a small shunt capacitance and moderate damping, resulting in a switching current which is a small fraction of the critical current. Phase locking between two JJs leads to a difference in switching current between that of a JJ measured in isolation and that of the same JJ measured in an asymmetric SQUID loop. In the case of the loop, T∗ is also tuned by a magnetic flux.
Strongly interacting two-dimensional electron systems: Evidence for enhanced one-dimensional edge-channel coupling
Marty, Christian; Reichl, Christian; Parolo, Simon; et al. (2023)
Physical Review B
We observe nearly vanishing Hall resistances for integer filling factors in a counterflow experiment on a density-balanced two-dimensional (2D) bilayer system. Filling-factor-dependent equilibration lengths demonstrate enhanced 1D coupling via edge channels. Due to the narrow barrier the edge modes of the two 2D electron gases are in close proximity allowing for exciton formation at the sample edges. Electron drag measurements confirm the observed quantum-state-selective coupling between the layers.
Charge qubit in a triple quantum dot with tunable coherence
Kratochwil, Benedikt; Koski, Jonne V.; Landig, Andreas J.; et al. (2021)
Physical Review Research
Fractional Coulomb blockade for quasi-particle tunneling between edge channels
Röösli, Marc P.; Hug, Michael; Nicoli, Giorgio; et al. (2021)
Science Advances
In the fractional quantum Hall effect, the elementary excitations are quasi-particles with fractional charges as predicted by theory and demonstrated by noise and interference experiments. We observe Coulomb blockade of fractional charges in the measured magneto-conductance of a 1.4-micron-wide quantum dot. Interaction-driven edge reconstruction separates the dot into concentric compressible regions with fractionally charged excitations and incompressible regions acting as tunnel barriers for quasi-particles. Our data show the formation of incompressible regions of filling factors 2/3 and 1/3. Comparing data at fractional filling factors to filling factor 2, we extract the fractional quasi-particle charge e*/e = 0.32 ± 0.03 and 0.35 ± 0.05. Our investigations extend and complement quantum Hall Fabry-Pérot interference experiments investigating the nature of anyonic fractional quasi-particles.
Spin-Selective Equilibration among Integer Quantum Hall Edge Channels
Nicoli, Giorgio; Adam, Christoph; Röösli, Marc P.; et al. (2022)
Physical Review Letters
The equilibration between quantum Hall edge modes is known to depend on the disorder potential and the steepness of the edge. Modern samples with higher mobilities and setups with lower electron temperatures call for a further exploration of the topic. We develop a framework to systematically measure and analyze the equilibration of many (up to 8) integer edge modes. Our results show that spin-selective coupling dominates even for non-neighboring channels with parallel spin. Changes in magnetic field and bulk density let us control the equilibration until it is almost completely suppressed and dominated only by individual microscopic scatterers. This method could serve as a guideline to investigate and design improved devices, and to study fractional and other exotic states.
Nonlinear response of a two-dimensional electron gas in the quantum Hall regime
Iwakiri, Shuichi; Ginzburg, Lev V.; Röösli, Marc P.; et al. (2023)
Physical Review Research
Breaking of inversion symmetry leads to nonlinear and nonreciprocal electron transport, in which the voltage response does not invert with the reversal of the current direction. Many systems have incorporated inversion symmetry breaking into their band or crystal structures. In this Letter, we demonstrate that a conventional two-dimensional electron gas system with a back gate shows nonreciprocal behavior (with voltage proportional to current squared) in the quantum Hall regime, which depends on the out-of-plane magnetic field and contact configuration. The inversion symmetry is broken due to the presence of the back gate and magnetic field, and our phenomenological model provides a qualitative explanation of the experimental data. Our results suggest a universal mechanism that gives rise to nonreciprocal behavior in gated samples.
Flip-Chip-Based Microwave Spectroscopy of Andreev Bound States in a Planar Josephson Junction
Hinderling, M.; Sabonis, Deividas; Paredes, Stephan; et al. (2023)
Physical Review Applied
We demonstrate a flip-chip-based approach to microwave measurements of Andreev bound states (ABSs) in a gate-tunable planar Josephson junction (JJ) using inductively coupled superconducting low-loss resonators. By means of electrostatic gating, we present control of both the density and transmission of ABSs. Phase biasing of the device shifted the resonator frequency, consistent with the modulation of supercurrent in the junction. Two-tone spectroscopy measurements revealed an isolated ABS consistent with an average induced superconducting gap of 184μeV and a gate-tunable transmission approaching 0.98. Our results represent the feasibility of using the flip-chip technique to address and study ABSs in planar JJs, and they constitute a promising path towards microwave applications with superconductor-semiconductor two-dimensional materials.

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Werner Wegscheider

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