In a two-dimensional electron system, microwave radiation may induce giant resistance oscillations. Their origin has been debated controversially and numerous mechanisms based on very different ...physical phenomena have been invoked. However, none of them have been unambiguously experimentally identified, since they produce similar effects in transport studies. The capacitance of a two-subband system is sensitive to a redistribution of electrons over energy states, since it entails a shift of the electron charge perpendicular to the plane. In such a system, microwave-induced magnetocapacitance oscillations have been observed. They can only be accounted for by an electron distribution function oscillating with energy due to Landau quantization, one of the quantum mechanisms proposed for the resistance oscillations.
We demonstrate the operation of a quantum spin pump based on cyclic radio-frequency excitation of a GaAs quantum dot, including the ability to pump pure spin without pumping charge. The device takes ...advantage of bidirectional mesoscopic fluctuations of pumped current, made spin dependent by the application of an in-plane Zeeman field. Spin currents are measured by placing the pump in a focusing geometry with a spin-selective collector.
We apply polarization resolved photoluminescence spectroscopy to measure the spin polarization of a two dimensional electron gas in perpendicular magnetic field. We find that the splitting between ...the σ+ and σ- polarizations exhibits a sharp drop at ν=5/2 and is equal to the bare Zeeman energy, which resembles the behavior at even filling factors. We show that this behavior is consistent with filling factor ν=5/2 being unpolarized.
We report the unexpected bunching of Laughlin's quasiparticles, induced by an extremely weak backscattering potential at exceptionally low electron temperatures (T<10 mK), deduced from shot noise ...measurements. Backscattered charges q=nue, specifically, q=e/3, q=2e/5, and q<3e/7, in the respective filling factors, were measured. For the same settings but at a slightly higher electron temperature, the measured backscattered charges were q=e/3, q=e/5, and q=e/7, as expected. Moreover, the backscattered current exhibited distinct temperature dependence that was correlated to the backscattered charge and the filling factor. This observation suggests the existence of "low" and "high" temperature backscattering states, each with its characteristic charge and energy.
The compressibility of electrons in a bilayer electron system implemented in a GaAs double quantum well is investigated. Manifestations of the negative compressibility of a low-density ...two-dimensional electron system in zero and quantizing magnetic fields are observed. It is found that the magnetic field ranges where incompressible phases at the spin-resolved Landau level filling factors of 2 and 1 exist in the layer with the higher electron density are broadened considerably upon the filling of the other layer. The effect is explained by the stabilization of the quantum Hall effect states owing to the transfer of electrons from the layer with the lower density. The magnitude of jumps in the chemical potential for the corresponding quantum Hall effect states is estimated.
The study presents the results of comparative laboratory tests of diamond tubular drills when drilling window glass, granite, and abrasive stones based on silicon carbide SiC. The tests were carried ...out in cold running water. Tin bronze containing micro- and ultradispersed diamond powders of ASM 40/28, ASM 10/7 (MDP), ASM 1/0 (UDDP) grades, and molybdenum powder were used as a matrix of the tool. Furthermore, the dependence of the hardness of specially prepared matrix samples on their composition was examined. With an increase in the ASM 1/0 concentration up to 5 wt.% in the reinforcement, the hardness of the matrix samples increased by one-third and reached a maximum of ~96.5 HRB. A further increase in the ASM 1/0 concentration led to a slight decrease in the hardness of the samples. The use of larger diamond powders required a higher concentration, providing high values of hardness. By adding ASM 10/7 in an amount of 10 wt.% and ASM 40/28 in the amount of 40–60 wt.% we managed to increase the hardness of the matrix to the same maximum. The introduction of a reinforcement in a bonding matrix of diamond tubular drills in amount ensuring its maximum hardness has significantly increased the efficiency of their operation. Thus, the wear of drills after glass processing decreased by 2–6 times, and the drilling speed increased by 3–4 times. Drill wear after granite processing has decreased by 50–84 times, and the drilling speed has increased 2.7–6 times, correspondingly. Finally, after processing of an abrasive stone based on silicon carbide SiC, the wear of diamond tubular drills decreased by 1.4– 2.9 times, and the drilling speed increased by 1.5–2.5 times. The effect of additives in the reinforcement of the tool depended on the choice of the diamond powder grade and their concentration. The best option was the introduction of ASM 1/0 (UDDP) powder in an amount of 5– 9 wt.%. The introduction of ASM 10/7, and especially ASM 40/28 (MDP), into the reinforcement required, firstly, their higher concentration (10–40 wt.%), and secondly, was not effective enough since the wear indicators of diamond tools were higher, and the drilling speed was lower.
Wave-particle duality, as manifest in the two-slit experiment, provides perhaps the most vivid illustration of Bohr's complementarity principle: wave-like behaviour (interference) occurs only when ...the different possible paths a particle can take are indistinguishable, even in principle. The introduction of a which-path (welcher Weg) detector for determining the actual path taken by the particle inevitably involved coupling the particle to a measuring environment, which in turn results in dephasing (suppression of interference). In other words, simultaneous observations of wave and particle behaviour is prohibited. Such a manifestation of the complementarity principle was demonstrated recently using a pair of correlated photons, with measurement of one photon being used to determine the path taken by the other and so prevent single-photon interference. Here we report the dephasing effects of a which-path detector on electrons traversing a double-path interferometer. We find that by varying the sensitivity of the detector we can affect the visibility of the oscillatory interference signal, thereby verifying the complementarity principle for fermions.
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