14 research outputs found
Dynamic metastable vortex states in interacting vortex lines
The electron transport in current-biased superconducting nano-bridges is
determined by the motion of the quantum vortex confined in the internal
disorder landscape. Here we consider a simple case of a single or two
neighbouring linear defects crossing a nano-bridge. The strong anharmonicity of
the vortex motion along the defect leads, upon RF-excitation, to fractional
Shapiro steps. In the case of two defects, the vortex motion becomes
correlated, characterized by metastable states that can be locked to a resonant
RF-drive. The lock-unlock process causes sudden voltage jumps and drops in the
voltage-current characteristics observed in experiments. We analyze the
parameters promoting these metastable dynamic states and discuss their
potential applications in quantum devices.Comment: 9 pages, 8 figure
Spin-Orbit induced phase-shift in BiSe Josephson junctions
The transmission of Cooper pairs between two weakly coupled superconductors
produces a superfluid current and a phase difference; the celebrated Josephson
effect. Because of time-reversal and parity symmetries, there is no Josephson
current without a phase difference between two superconductors. Reciprocally,
when those two symmetries are broken, an anomalous supercurrent can exist in
the absence of phase bias or, equivalently, an anomalous phase shift
can exist in the absence of a superfluid current. We report on the
observation of an anomalous phase shift in hybrid Josephson
junctions fabricated with the topological insulator BiSe submitted to
an in-plane magnetic field. This anomalous phase shift is observed
directly through measurements of the current-phase relationship in a Josephson
interferometer. This result provides a direct measurement of the spin-orbit
coupling strength and open new possibilities for phase-controlled Josephson
devices made from materials with strong spin-orbit coupling
Extremely sub-wavelength THz metal-dielectric wire microcavities
We demonstrate minimal volume wire THz metal-dielectric micro-cavities, in which all but one dimension have been reduced to highly sub-wavelength values. The smallest cavity features an effective volume of 0.4 µm(3), which is ~5.10(-7) times the volume defined by the resonant vacuum wavelength (λ = 94 µm) to the cube. When combined with a doped multi-quantum well structure, such micro-cavities enter the ultra-strong light matter coupling regime, even if the total number of electrons participating to the coupling is only in the order of 10(4), thus much less than in previous studies
Anomalous microwave response in the dissipative regime of topological superconducting devices based on Bi2Te2.3Se0.7
Superconducting proximity junctions based on topological insulators are
widely believed to harbor Majorana-like bound states. The latter serves as a
paradigm non-local topological quantum computation protocols. Nowadays, a
search for topological phases in different materials, perspective for a
realization of topological qubits, is one of the central efforts in quantum
physics. It is motivated, in particular, by recent observation of anomalous ac
Josephson effect, which being a signature of Majorana physics. Its
manifestations, such as a fractional Josephson frequency and the absence of the
first (or several odd in more rare cases), Shapiro steps, were reported for
different materials. Here we study Shapiro steps in Nb/Bi2Te2.3Se0.7/Nb
junctions, based on ultrasmall single crystals of a 3D topological insulator
synthesized by a physical vapor deposition (PVD) technique. We present evidence
that our junctions are ballistic. When subjected to microwave radiation, the
junctions exhibit Shapiro steps, but the first step is missing. Typically it is
assumed that the missing first step (MFS) effect cannot be observed in the
presence of quasiparticle poisoning due to suppression of the 4{\pi}-periodic
component. Our findings within the context of the RSJ-model of Josephson
junction dynamics show that such behaviour of samples corresponds to a specific
condition, requiring a minimum of 5% of the 4{\pi}-component for disappearance
of the first Shapiro step.Comment: Keywords: Shapiro step missing, Topological insulator,
Superconductivity, Ballistic transport, 4{\pi}-periodic componen
Present and future of high-temperature superconductor quantum-based voltage standards
This paper presents a brief overview of the current state-of-the-art of Josephson junctions for Quantum-based Voltage Standards fabricated with High-Temperature Superconductors (HTS). A short introduction on the history and technical evolution of Low Temperature Superconductors (LTS) technology is provided for non-specialists. Then HTS technology is summarized and discussed in the context of quantum voltage standard applications. Finally, the two most promising technologies: bicrystal and Focused Helium-Ion Beam junctions are discussed with more detail, analyzing strength, limitations and perspectives in both cases
Vers une électronique de spin cohérente de phase à base de nanotubes de carbone
Cette thèse se place dans le cadre de la physique mésoscopique et a pour objet l'étude du transport électronique polarisé en spin dans les nanotubes de carbone mono-parois. L'existence d'un déséquilibre entre les populations d'électrons de spin up et ceux de spin down lors de leur diffusion à l'interface entre un métal ferromagnétique et un métal non-magnétique est au cœur du principe de fonctionnement des jonctions tunnel magnétiques et des multi-couches bien connues dans le domaine de l'électronique de spin. Bien que le degré de liberté de spin et l'effet tunnel des électrons soient utilisés dans ces dispositifs, aucun d'entre eux ne tient compte du degré de liberté de phase orbitale de la fonction d'onde électronique. Dans la plupart des dispositifs étudiés jusqu'à présent, cet aspect n'a pas été développé en raison du régime de transport semi-classique des porteurs de charge dans les conducteurs considérés. Dans ce travail, nous étudions des mesures de transport dépendantes du spin dans des circuits à plusieurs réservoirs à base de nanotubes de carbone. Nous observons la présence d'un signal de spin dans la tension non-locale et d'un signal de spin anormale dans la conductance. Ces signaux de spin sont contrôlables par la tension de grille appliquée et ils révèlent qu'à la fois le degré de liberté de phase orbitale et le degré de spin sont conservés dans un nanotube de carbone connecté à plusieurs réservoirs ferromagnétiques.Nous montrons également l'existence d'un phénomène étonnant qui n'a aucun analogue classique et qui est la conséquence de la cohérence de phase orbitale : la présence d'un comportement de type transistor de spin à effet de champ entre les deux contacts normaux avec à proximité deux contacts ferromagnétiques en dehors du chemin classique des électrons. Ceci est la réalisation de l'expérience de tête de théoricien pour l'électronique de spin. Nos observations ouvrent la voix pour des dispositifs de l'électronique de spin exploitant ces deux degré de liberté quantique sur le même plan.PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF