Photovoltaic Probe of Cavity Polaritons in a Quantum Cascade Structure

The strong coupling between an intersubband excitation in a quantum cascade structure and a photonic mode of a planar microcavity has been detected by angle-resolved photovoltaic measurements. A typical anticrossing behavior, with a vacuum-field Rabi splitting of 16 meV at 78K, has been measured, for an intersubband transition at 163 meV. These results show that the strong coupling regime between photons and intersubband excitations can be engineered in a quantum cascade opto-electronic device. They also demonstrate the possibility to perform angle-resolved mid-infrared photodetection and to develop active devices based on intersubband cavity polaritons.Comment: submitted to Applied Physics Letter

Observation of non-Hermitian topology in a multi-terminal quantum Hall device

Quantum devices characterized by non-Hermitian topology are predicted to show highly robust and potentially useful properties, but realizing them has remained a daunting experimental task. This is because non-Hermiticity is often associated with gain and loss, which would require precise tailoring to produce the signatures of nontrivial topology. Here, instead of gain/loss, we use the nonreciprocity of the quantum Hall edge states to directly observe non-Hermitian topology in a multi-terminal quantum Hall ring. Our transport measurements evidence a robust, non-Hermitian skin effect: currents and voltages show an exponential profile, which persists also across Hall plateau transitions away from the regime of maximum non-reciprocity. Our observation of non-Hermitian topology in a quantum device introduces a scalable experimental approach to construct and investigate generic non-Hermitian systems

Limite quantique du flux de chaleur

International audienceLa théorie quantique est le socle sur lequel repose notre compréhension de la nature. Bien qu’elle ait été élaborée il y a presque un siècle, l’établissement expérimental de ses fondements se poursuit. En particulier, l’exploration des aspects quantiques du transport de chaleur n’en est qu’à ses débuts. Nous présentons ici la démonstration expérimentale d’une des pierres angulaires du transport de la chaleur en régime quantique, l’existence d’une limite maximum fondamentale à la conduction thermique appelée, pour un canal élémentaire de transport, le quantum de conductance thermique.Ce quantum, ici mesuré dans un système électronique et égal à 1 pW/K à une température de 1 K, est prédit complètement universel, indépendant même du mécanisme de conduction thermique

Suspended two-dimensional electron and hole gases

International audienceWe report on the fabrication of fully suspended two-dimensional electron and hole gases in III-V heterostructures. Low temperature transport measurements verify that the properties of the suspended gases are only slightly degraded with respect to the non-suspended gases. Focused ion beam technology is used to pattern suspended nanostructures with minimum damage from the ion beam, due to the small width of the suspended membrane

Electrochemical Capacitance and Transit Time in Quantum Hall Conductors

International audienceIn a two dimensional electron gas, low energy transport in presence of a magnetic field occurs in chiral 1D channels located on the edge of the sample. In the AC description of quantum transport, the emittance determines the amplitude of the imaginary part of the admittance, whose sign and physical meaning are determined by the sample topology: a Hall bar is inductive while a Corbino ring is capacitive. In this article, the perfect capacitive character of Corbino samples in the quantum Hall effect regime is shown. A vanishing conductance and an electrochemical capacitance which depends on the density of states of 1D channels are measured. Our samples have no gate, neither on the side nor on the top, and the inner capacitances are measured. The transit time of electrons across the device is obtained and the drift velocity of carriers is deduced

Spin filtering through a single impurity in a GaAs/AlAs/GaAs resonant tunneling device

International audienceThe Zeeman splittings of a Si shallow donor in AlAs and of a two-dimensional electron gas (2DEG) in GaAs are evidenced by resonant tunneling spectroscopy in submicrometer GaAs/AlAs/GaAs junctions. In magnetic field, the donor acts as a spin-sensitive probe of the spin-polarized density of states in the emitter. In the current-voltage characteristic the two splittings are resolved, which allows us to estimate the Landé g factors for the impurity gI=+1.96±0.16 and for the 2DEG. Because of spin conservation in the tunneling between the 2DEG and the donor, the relative sign of the two g factors can be determined