We study the visibility of Aharonov-Bohm interference in an electronic Mach-Zehnder interferometer in the integer quantum Hall regime. The visibility is controlled by the filling factor and is observed only between Ϸ 2.0 and 1.0, with an unexpected maximum near = 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.
We study nonlocal vortex transport in mesoscopic amorphous Nb 0.7 Ge 0.3 samples. A dc current I is passed through a wire connected via a perpendicular channel, of a length L =2-5 m, with a pair of voltage probes where a nonlocal response V nl ϰ I is measured. The maximum of R nl = V nl / I for a given temperature occurs at an L-independent magnetic field and is proportional to 1 / L. The results are interpreted in terms of the dissipative vortex motion along the channel driven by a remote current and can be understood in terms of a simple model. DOI: 10.1103/PhysRevB.74.220510 PACS number͑s͒: 74.78.Na, 74.78.Db, 74.25.Qt, 74.25.Fy In a pioneering work Giaver measured a magnetic-fluxtransformer effect in type-II superconductors. 1 He applied a magnetic field B perpendicularly to a sample comprising two superconducting sheets separated by a thin insulator, passed a current I through one of the superconductors, and measured a voltage developed over the other one-where no current was flowing. The induced voltage was a consequence of an electromagnetic coupling of vortices in the two layers. In their recent experiment Grigorieva et al. 2 demonstrated a complementary flux-transformer phenomenon associated with vortices. They produced mesoscopic amorphous MoGe structures of a double-cross shape, consisting of two parallel wires connected at a right angle by a channel of width w = 0.07-2 m and a length L = 0.5-12 m. In a perpendicular B and with I through one of the parallel wires a nonlocal voltage V nl appeared over the second, current-free wire. This novel, transversal flux-transformer effect originated in the in-plane vortex-vortex repulsion, which conveyed the driving force from the current-carrying wire to the vortices in the channel. The effect disappeared not only for L exceeding 6 -7 m but also for w larger than ϳ0.5-1 m. When w was sufficiently small the force on the vortices in the channel was transferred over many intervortex distances and, moreover, V nl was proportional to I. The efficiency of the transversal flux-transformer effect can be quantified by a nonlocal resistance R nl = V nl / I.In the experiment of Grigorieva et al. 2 the local mixedstate dissipation was characterized on separate mm-sized films, whereas V nl was measured by a low-frequency ac method during B sweeps at constant temperatures T. An ac method was used because V nl was in nV range-i.e., R nl Ͻ 5 m⍀-thus being too small for dc detection. In our work we focused on dc probing of the transversal fluxtransformer effect and measuring V nl and the local voltage V l on the same sample, which was possible in multiterminal amorphous ͑a − ͒Nb 0.7 Ge 0.3 structures of the geometry shown in the inset to Fig. 1. The weak pinning, characteristic of the a −Nb 0.7 Ge 0.3 material used, resulted in a dc-measurable V nl and R nl ϳ 1 ⍀ even at very low temperatures. The measured nonlocal resistance was hence two orders of magnitude larger than in Ref. 2. In this study we investigate the transversal fluxtransformer effect in samples of different...
We investigate an electronic Mach-Zehnder 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 π in the interference pattern.
It was recently suggested that a novel type of phase transition may occur in the visibility of electronic Mach-Zehnder interferometers. Here, we present experimental evidence for the existence of this transition. The transition is induced by strongly non-Gaussian noise that originates from the strong coupling of a quantum point contact to the interferometer. We provide a transparent physical picture of the effect by exploiting a close analogy to the neutrino oscillations of particle physics. In addition, our experiment constitutes a probe of the singularity of the elusive full counting statistics of a quantum point contact. The recent discovery of a lobe-type behavior in the visibility of Aharonov-Bohm oscillations in electronic Mach-Zehnder interferometers (MZI) has triggered extensive theoretical studies in this field. These interferometers were implemented in the edge channels in the integer quantum Hall effect (QHE), mostly for filling factor ff = 2 [see Figs. 1(a) and 1(b)] [1-3]. Many sophisticated theories have been proposed to explain the lobes in the differential visibility of Aharonov-Bohm oscillations as a function of the voltage bias [4][5][6][7][8][9][10][11]. While the central lobe and next side lobe are easy to explain, observation of additional side lobes in a number of experiments is considered to be a puzzling phenomenon. Here, we show that this effect can be explained in a rather simple way, if two interacting edge channels are present. The underlying phenomenon turns out to be very similar to that of neutrino oscillations in high-energy physics: neutrinos oscillate between different flavor states because they are created in a flavor eigenstate, which is not an eigenstate of the Hamiltonian. Similarly, when an electron wave packet is partitioned by a beam splitter, it excites a collective charge mode, which is not an eigenstate of our model Hamiltonian [6]. At the second beam splitter of the interferometer, this leads to a secondary interference between the collective modes as a function of the applied voltage bias. This model can explain many of the experimental observations [12][13][14][15][16], most importantly the visibility lobes [17] and the phase rigidity of the visibility [1,2].Dephasing of the Aharanov-Bohm interference results from random fluctuations of the phase that are averaged out by the detector. In our devices, fluctuations are generated by an additional quantum point contact (QPC-0) in front of the interferometer input, which can be controlled by its transmission probability T 0 . The noisy input current leads to charge fluctuations in the interferometer. The accumulated charge shifts the edge, which leads to the Aharonov-Bohm phase shift. Hence, the strong Coulomb interaction between the edge channels guarantees a strong coupling of the electrons in the interferometer to the noise. The visibility will thus be suppressed by the charge fluctuations induced by partitioning of electrons at QPC-0. Most interestingly, the lobe pattern was predicted to undergo a sudden change at T ...
We performed the conductance and the shot noise measurements in an electronic Mach-Zehnder interferometer. The visibility of the interference is investigated as a function of the electron temperature that is derived from the thermal noise of the interferometer. The non-equilibrium noise displays both h/e and h/2e oscillations vs. the modulation gate voltage.
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