Dirac fermion optics exploits the refraction of chiral fermions across optics-inspired Klein-tunneling barriers defined by high-transparency p-n junctions. We consider the corner reflector (CR) ...geometry introduced in optics or radars. We fabricate Dirac fermion CRs using bottom-gate-defined barriers in hBN-encapsulated graphene. By suppressing transmission upon multiple internal reflections, CRs are sensitive to minute phonon scattering rates. Here we report on doping-independent CR transmission in quantitative agreement with a simple scattering model including thermal phonon scattering. As a signature of CRs, we observe Fabry-Pérot oscillations at low temperature, consistent with single-path reflections. Finally, we demonstrate high-frequency operation which promotes CRs as fast phonon detectors. Our work establishes the relevance of Dirac fermion optics in graphene and opens a route for its implementation in topological Dirac matter.
We study the decoherence and relaxation of a single elementary electronic excitation propagating in a one-dimensional chiral conductor. Using two-particle interferences in the electronic analog of ...the Hong-Ou-Mandel experiment, we analyze quantitatively the decoherence scenario of a single electron propagating along a quantum Hall edge channel at filling factor 2. The decoherence results from the emergence of collective neutral excitations induced by Coulomb interaction and leading, in one dimension, to the destruction of the elementary quasiparticle. This study establishes the relevance of electron quantum optics setups to provide stringent tests of strong interaction effects in one-dimensional conductors described by the Luttinger liquids paradigm.
Carrier mobility in solids is generally limited by electron-impurity or electron-phonon scattering, depending on the most frequently occurring event. Three-body collisions between carriers and both ...phonons and impurities are rare; they are denoted supercollisions. Elusive in electronic transport they should emerge in relaxation processes as they allow for larger energy transfers. This is the case in undoped graphene, where the small Fermi surface drastically restricts the allowed phonon energy in ordinary collisions. Using electrical heating and sensitive noise thermometry we report on supercollision cooling in diffusive monolayer graphene. At low carrier density and high phonon temperature the Joule power P obeys a P Te3 law as a function of electronic temperature Te. It overrules the linear law expected for ordinary collisions which has recently been observed in resistivity measurements. The cubic law is characteristic of supercollisions and departs from the Te4 dependence recently reported for doped graphene below the Bloch-Grüneisen temperature. These supercollisions are important for applications of graphene in bolometry and photo-detection. PUBLICATION ABSTRACT
Squeezing of the quadratures of the electromagnetic field has been extensively studied in optics and microwaves. However, previous works focused on the generation of squeezed states in a low ...impedance (Z_{0}≈50 Ω) environment. We report here on the demonstration of the squeezing of bosonic edge magnetoplasmon modes in a quantum Hall conductor whose characteristic impedance is set by the quantum of resistance (R_{K}≈25 kΩ), offering the possibility of an enhanced coupling to low-dimensional quantum conductors. By applying a combination of dc and ac drives to a quantum point contact, we demonstrate squeezing and observe a noise reduction 18% below the vacuum fluctuations. This level of squeezing can be improved by using more complex conductors, such as ac driven quantum dots or mesoscopic capacitors.
Two‐particle interferometry in quantum Hall edge channels Marguerite, A.; Bocquillon, E.; Berroir, J.‐M. ...
Physica Status Solidi. B: Basic Solid State Physics,
March 2017, 2017-03-00, 20170301, 2017-03, Volume:
254, Issue:
3
Journal Article
Peer reviewed
Open access
Since the pioneering works of Hanbury‐Brown and Twiss, intensity–intensity correlations have been widely used in astronomical systems, for example, to detect binary stars. They reveal statistics ...effects and two‐particle interference, and offer a decoherence‐free probe of the coherence properties of light sources. In the quantum Hall edge channels, the concept of quantum optics can be transposed to electrons, and an analogous two‐particle interferometry can be developed, in order to characterize single‐electron states. We review in this article the recent experimental and theoretical progress on this topic.
Two‐photon interferometry has been widely used in astronomical systems since the late 1950s, for example to detect binary stars. In quantum Hall edge channels, this concept can be transposed to electrons propagating in electron quantum optics devices. Two‐particle interferometry then reveals statistics effects and provides means to characterize an electronic quantum state. In this Feature Article, the recent experimental and theoretical progress in the field is reviewed.
In the original discussion of the Kondo effect, the increase of the resistance in an alloy such as Cu0.998Fe0.002 at low temperature was explained by the antiferromagnetic coupling between a magnetic ...impurity and the spin of the host's conduction electrons. This coupling has since emerged as a very generic property of localized electronic states coupled to a continuum. Recently, the possibility to design artificial magnetic impurities in nanoscale conductors has opened avenues to the study of this many-body phenomenon in a controlled way and, in particular, in out-of-equilibrium situations. So far though, measurements have focused on the average current. Current fluctuations (noise) on the other hand are a sensitive probe that contains detailed information about electronic transport. Here, we report on noise measurements in artificial Kondo impurities realized in carbon-nanotube devices. We find a striking enhancement of the current noise within the Kondo resonance, in contradiction with simple non-interacting theories. Our findings provide a sensitive test bench for one of the most important many-body theories of condensed matter in out-of-equilibrium situations and shed light on the noise properties of highly conductive molecular devices.
Anyon collision experiments have recently demonstrated the ability to discriminate between fermionic and anyonic statistics. However, only one type of anyons associated with the simple Laughlin state ...at filling factorν=1/3has been probed so far. It is now important to establish anyon collisions as quantitative probes of fractional statistics for more complex topological orders, with the ability to distinguish between different species of anyons with different statistics. In this work, we use the anyon collider to compare the Laughlinν=1/3state, which is used as the reference state, with the more complex Jain state atν=2/5, where low energy excitations are carried by two copropagating edge channels. We demonstrate that anyons generated on the outer channel of theν=2/5state (with a fractional chargee*=e/3) have a similar behavior compared toν=1/3, showing the robustness of anyon collision signals for anyons of the same type. In contrast, anyons emitted on the inner channel ofν=2/5(with a fractional chargee*=e/5) exhibit a reduced degree of bunching compared to theν=1/3case, demonstrating the ability of the anyon collider to discriminate not only between anyons and fermions, but also between different species of anyons associated with different topological orders of the bulk. Our experimental results for the inner channel ofν=2/5also point toward an influence of interchannel interactions in anyon collision experiments when several copropagating edge channels are present. A quantitative understanding of these effects will be important for extensions of anyon collisions to non-Abelian topological orders, where several charged and neutral modes propagate at the edge.
We have investigated electron dynamics in top gated graphene by measuring the gate admittance of a diffusive graphene capacitor in a broad frequency range as a function of carrier density. The ...density of states, conductivity, and diffusion constant are deduced from the low-frequency gate capacitance, its charging time, and their ratio. The admittance evolves from an rc-like to a skin-effect response at GHz frequency with a crossover given by the Thouless energy. The scattering time is found to be independent of energy in the 0- to 200-meV investigated range at room temperature. This is consistent with a random mass model for Dirac fermions.
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