Separation of neutral and charge modes in one dimensional chiral edge channels

Coulomb interactions have a major role in one-dimensional electronic transport. They modify the nature of the elementary excitations from Landau quasiparticles in higher dimensions to collective excitations in one dimension. Here we report the direct observation of the collective neutral and charge modes of the two chiral co-propagating edge channels of opposite spins of the quantum Hall effect at filling factor 2. Generating a charge density wave at frequency f in the outer channel, we measure the current induced by inter-channel Coulomb interaction in the inner channel after a 3-mm propagation length. Varying the driving frequency from 0.7 to 11 GHz, we observe damped oscillations in the induced current that result from the phase shift between the fast charge and slow neutral eigenmodes. We measure the dispersion relation and dissipation of the neutral mode from which we deduce quantitative information on the interaction range and parameters.Comment: 23 pages, 6 figure

Coherence and Indistinguishability of Single Electrons Emitted by Independent Sources

The on-demand emission of coherent and indistinguishable electrons by independent synchronized sources is a challenging task of quantum electronics, in particular regarding its application for quantum information processing. Using two independent on-demand electron sources, we trigger the emission of two single-electron wavepackets at different inputs of an electronic beamsplitter. Whereas classical particles would be randomly partitioned by the splitter, we observe two-particle interferences resulting from quantum exchange. Both electrons, emitted in indistinguishable wavepackets with synchronized arrival time on the splitter, exit in different outputs as recorded by the low frequency current noise. The demonstration of two-electron interference provides the possibility to manipulate coherent and indistinguishable single-electron wavepackets in quantum conductors.Comment: Science Express of January 24 201

Discussion on “Stable eutectoid transformation in nodular cast iron: modeling and validation”

The Minerals, Metals & Materials Society and ASM International 2017 Given that cast irons are multicomponent alloys, the decomposition of the high temperature austenite into ferrite and graphite happens within a finite temperature range and not at an invariant point, as often described schematically. Only a few models explicitly consider the existence of such an austenite–ferrite–graphite range: the contribution under discussion,[1]those that inspired it[2,3] and one previous study from the present author.[4]For kinetics reasons, this latter work explained that ferrite could not grow within the equilibrium three-phase field under continuous cooling; this is in contradiction with the other three reports. The aim of this discussion is first to recall the experimental evidence about ferrite formation during eutectoid transformation of cast iron and then to provide an explanation as to why ferrite starts forming upon cooling only when the temperature of the material is below the equilibrium three-phase field range, as observed experimentally

Study of the Eutectoid Transformation in Nodular Cast Irons in Relation to Solidification Microsegregation

Eutectoid transformation in cast irons may proceed in the stable or the metastable systems giving ferrite and graphite for the former and pearlite for the latter. The present work demonstrates that composition profiles across ferrite/pearlite boundaries are smooth and similar to those issued from the solidification step. No trace of long-range diffusion of substitutional solutes due to austenite decomposition could be observed. In turn, this ascertains that both stable and metastable transformations proceed with the product matrix—either ferrite opearlite—inheriting the parent austenite content in substitutional solutes. This result sustains a physical model for eutectoid transformation based on the so-called local para-equilibrium which is commonly used for describing solid-state transformation in steels

Reply to the Letter to the Editor

International audienceIn his discussion of our paper,[1] Doru M. Stefanescu first stresses that the presence of carbides in the as-cast samples he investigated with Guo was mentioned in one of their other papers,[2] not the one[3] we referenced. It is agreed that the presence of carbides was clearly stated in the first paper by Guo and Stefanescu;[2] however, the authors mentioned that ‘‘When the segregation of Cr and/or Mn reached a certain level, complex carbides of the (Fe,Mn)3C or (Fe,Cr)3C may form’’ in their second paper[3] on page 439. As the alloys and experimental conditions were exactly the same in both of their studies,it was presumed—perhaps improperly—that both studies therefore dealt with the same samples, and this sentence was understood to mean that the authors indicated the possible presence of some carbides in their samples

Intensity correlations of a single electron beam

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G.: Coherence and Indistinguishability of Single Electrons Emitted by Independent Sources

As for photons, the wave-particle duality plays a crucial role in the propagation of electrons in quantum conductors. The wave nature of electrons can be revealed in interference experiments (1-3) probing the single-particle coherence of electron sources through the measurement of the average electrical current. The corpuscular nature of charge carriers shows up when measuring fluctuations of the electrical current (4). Still, a few experiments cannot be understood within the wave nor the corpuscular description: this is the case when two-particle interferences effects related to the exchange between two indistinguishable particles take place. These experiments have proven particularly interesting, first on a fundamental point of view as they require a full quantum treatment, and secondly, because the on-demand generation of indistinguishable partners is at the heart of quantum information protocols (5). Information coding in few electron states that propagate ballistically in quantum conductors (6) thus requires the production of coherent and indistinguishable single-particle wavepackets emitted by several synchronized but otherwise independent emitters. The collision of two particles emitted at two different inputs of a beamsplitter can be used to measure their degree of indistinguishability. In the case of bosons, indistinguishable partners always exit in the same output (see The production of indistinguishable partners is challenging and their generation by independent sources has been only recently achieved in optics (8). In one dimensional quantum conductors, a continuous stream of indistinguishable electrons can be produced by applying a dc voltage bias to two different electronic reservoirs. Due to fermionic statistics, each source fills the electronic states up to the chemical potential −eV and identical electron beams are generated. Using such sources, the π exchange phase of indistinguishable fermions has been measured in the above described collider geometry (9) and in a two-particle interferometer based on a MachZehnder geometry (10, 11). However, as these sources generate a continuous beam of electrons, they do not reach the single particle resolution of their optical analog and two-particle interferences cannot be interpreted as resulting from the overlap between two single particle wavepackets. The manipulation of single-particle states thus requires to replace dc emitters by triggered ac emitters that generate a single-electron wavepacket at a well defined time. Dealing with electrons, one can benefit from the charge quantization of a small quantum dot enforced both by Coulomb interaction and fermionic statistics to trigger the emission of particles one by one (12-16). Moreover, the edge channels of the quantum Hall effect provide an ideal test bench to implement optic-like experiments with electron beams in condensed matter, as electron propagation is ballistic, one-dimensional and chiral. We will consider here a mesoscopic capacitor (12), which comprises a small quantum dot capacitively coupled to a metallic top gate and tunnel coupled to a single edge channel by a quantum point contact of variable transmission D. By applying a square wave periodic rf excitation on the top gate which peak to peak amplitude matches the dot addition energy, 2eV exc ≈ ∆, a quantized current resulting from the emission of a single electron followed by a single hole is generated (12). Beyond average current measurements, this emitter has been characterized through the study of current correlations on short times (17-20) as well as partition noise measurements (21) in the electronic analog of the Hanbury-Brown and Twiss geometr

Coherence and indistinguishability of single electron wavepackets emitted by independent sources

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