Étude par spectroscopie de coulomb d'une boîte quantique latérale contenant de 1 à 12 électrons

Une boîte quantique contenant un nombre discret et variable d'électrons est formée dans un gaz bi-dimensionnel d'électrons. On explique concrètement comment la géométrie des grilles utilisées pour former la boîte permet de contrôler exactement le nombre d'électrons jusqu'à zéro. Ce contrôle nous permet d'obtenir, par transport dans le régime de blocage de Coulomb, les spectres d'addition et d'excitation associés à l'ajout des 12 premiers électrons dans la boîte. On montre que le potentiel de confinement peut être approximé, près de son minimum, par celui d'un oscillateur harmonique dont l'énergie caractéristique est de l'ordre du meV. Ce résultat permet de calibrer l'énergie d'addition du premier électron et d'obtenir la variation en champ magnétique B du niveau de Fermi du gaz électronique bi-dimensionnel (GE2D) utilisé comme réservoir pour le transport à travers la boîte. Le résultat montre une oscillation périodique en 1/ B avec une amplitude beaucoup plus petite que l'énergie cyclotron. On observe ensuite la transition en champ magnétique entre les deux états de plus basse énergie d'une boîte contenant 2 électrons, soient les états singulet et triplet. On montre que l'approximation harmonique cesse d'être valide pour une boîte contenant plus d'un électron. Les résultats montrent que le champ critique de la transition dépend du potentiel appliqué sur les grilles. De plus, on observe une modulation de l'amplitude du courant circulant à travers la boîte lors de la transition. On attribue cette modulation à l'injection partiellement polarisée en spin, causée par la séparation spatiale des états de bords du GE2D de spin «1/2. Finalement, les résultats pour un plus grand nombre d'électrons montrent que l'hypothèse de l'injection partiellement polarisée est en accord avec les transitions en champ magnétique des configurations électroniques de la boîte et qu'elle permet de mesurer, par l'amplitude du courant, le spin total de la boîte

Microwave band on-chip coil technique for single electron spin resonance in a quantum dot

Microwave band on-chip microcoils are developed for the application to single electron spin resonance measurement with a single quantum dot. Basic properties such as characteristic impedance and electromagnetic field distribution are examined for various coil designs by means of experiment and simulation. The combined setup operates relevantly in the experiment at dilution temperature. The frequency responses of the return loss and Coulomb blockade current are examined. Capacitive coupling between a coil and a quantum dot causes photon assisted tunneling, whose signal can greatly overlap the electron spin resonance signal. To suppress the photon assisted tunneling effect, a technique for compensating for the microwave electric field is developed. Good performance of this technique is confirmed from measurement of Coulomb blockade oscillations.Comment: 7 pages, 8 figures, Accepted for publication in Rev. Sci. Instrum. The bibliography file is update

Probing a spin transfer controlled magnetic nanowire with a single nitrogen-vacancy spin in bulk diamond

The point-like nature and exquisite magnetic field sensitivity of the nitrogen vacancy (NV) center in diamond can provide information about the inner workings of magnetic nanocircuits in complement with traditional transport techniques. Here we use a single NV in bulk diamond to probe the stray field of a ferromagnetic nanowire controlled by spin transfer (ST) torques. We first report an unambiguous measurement of ST tuned, parametrically driven, large-amplitude magnetic oscillations. At the same time, we demonstrate that such magnetic oscillations alone can directly drive NV spin transitions, providing a potential new means of control. Finally, we use the NV as a local noise thermometer, observing strong ST damping of the stray field noise, consistent with magnetic cooling from room temperature to $\sim$150 K.Comment: 6 pages, 5 figures, plus supplementary informatio

Analog programming of CMOS-compatible Al2_2O3_3/TiO2-x_\textrm{2-x} memristor at 4.2 K after metal-insulator transition suppression by cryogenic reforming

The exploration of memristors' behavior at cryogenic temperatures has become crucial due to the growing interest in quantum computing and cryogenic electronics. In this context, our study focuses on the characterization at cryogenic temperatures (4.2 K) of TiO$_\textrm{2-x}$-based memristors fabricated with a CMOS-compatible etch-back process. We demonstrate a so-called cryogenic reforming (CR) technique performed at 4.2 K to overcome the well-known metal-insulator transition (MIT) which limits the analog behavior of memristors at low temperatures. This cryogenic reforming process was found to be reproducible and led to a durable suppression of the MIT. This process allowed to reduce by approximately 20% the voltages required to perform DC resistive switching at 4.2 K. Additionally, conduction mechanism studies of memristors before and after cryogenic reforming from 4.2 K to 300 K revealed different behaviors above 100 K, indicating a potential change in the conductive filament stoichiometry. The reformed devices exhibit a conductance level that is 50 times higher than ambient-formed memristor, and the conduction drop between 300 K and 4.2 K is 100 times smaller, indicating the effectiveness of the reforming process. More importantly, CR enables analog programming at 4.2 K with typical read voltages. Suppressing the MIT improved the analog switching dynamics of the memristor leading to approximately 250% larger on/off ratios during long-term depression (LTD)/long-term potentiation (LTP) resistance tuning. This enhancement opens up the possibility of using TiO$_{\textrm{2-x}}$-based memristors to be used as synapses in neuromorphic computing at cryogenic temperatures

A silicone nanocrystal tunnel field effect transistor

Abstract : In this work, we demonstrate a silicon nanocrystal Field Effect Transistor (ncFET). Its operation is similar to that of a Tunnelling Field Effect Transistor (TFET) with two barriers in series. The tunnelling barriers are fabricated in very thin silicon dioxide and the channel in intrinsic polycrystalline silicon. The absence of doping eliminates the problem of achieving sharp doping profiles at the junctions, which has proven a challenge for large-scale integration and, in principle, allows scaling down the atomic level. The demonstrated ncFET features a 104 on/off current ratio at room temperature, a low 30pA/lm leakage current at a 0.5V bias, an on-state current on a par with typical all-Si TFETs and bipolar operation with high symmetry. Quantum dot transport spectroscopy is used to assess the band structure and energy levels of the silicon island