776 research outputs found
Interplay of Kondo effect and strong spin-orbit coupling in multi-hole ultraclean carbon nanotubes
We report on cotunneling spectroscopy magnetoconductance measurements of
multi-hole ultraclean carbon nanotube quantum dots in the SU(4) Kondo regime
with strong spin-orbit coupling. Successive shells show a gradual weakening of
the Kondo effect with respect to the spin-orbital splittings, leading to an
evolution from SU(4) to SU(2) symmetry with a suppressed conductance at half
shell filling. The extracted energy level spectrum, overally consistent with
negligible disorder in the nanotube, shows in the half filled case large
renormalizations due to Coulombian effects.Comment: 5 pages, 4 figures, 1 supplementary fil
Gate-tuned high frequency response of carbon nanotube Josephson junctions
Carbon nanotube (CNT) Josephson junctions in the open quantum dot limit
exhibit superconducting switching currents which can be controlled with a gate
electrode. Shapiro voltage steps can be observed under radiofrequency current
excitations, with a damping of the phase dynamics that strongly depends on the
gate voltage. These measurements are described by a standard RCSJ model showing
that the switching currents from the superconducting to the normal state are
close to the critical current of the junction. The effective dynamical
capacitance of the nanotube junction is found to be strongly gate-dependent,
suggesting a diffusive contact of the nanotube.Comment: 14 pages, 8 figure
Magneto-Coulomb Effect in Carbon Nanotube Quantum Dots Filled with Magnetic Nanoparticles
Electrical transport measurements of carbon nanotubes filled with magnetic iron nanoparticles are reported. Low-temperature (40 mK) magnetoresistance measurements showed conductance hysteresis with sharp jumps at the switching fields of the nanoparticles. Depending on the gate voltage, positive or negative hysteresis was observed. The results are explained in terms of a magneto-Coulomb effect: The spin flip of the iron island at a nonzero magnetic field causes a shift of the chemical potential induced by the change of Zeeman energy; i.e., an effective charge variation is detected by the nanotube quantum dot
Blocking transport resonances via Kondo entanglement in quantum dots
Many-body entanglement is at the heart of the Kondo effect, which has its
hallmark in quantum dots as a zero-bias conductance peak at low temperatures.
It signals the emergence of a conducting singlet state formed by a localized
dot degree of freedom and conduction electrons. Carbon nanotubes offer the
possibility to study the emergence of the Kondo entanglement by tuning
many-body correlations with a gate voltage. Here we quantitatively show an
undiscovered side of
Kondo correlations, which counterintuitively tend to block conduction
channels: inelastic cotunneling lines in the magnetospectrum of a carbon
nanotube strikingly disappear when tuning the gate voltage. Considering the
global \SUT\ \SUT\ symmetry of a carbon nanotube coupled to leads,
we find that only resonances involving flips of the Kramers pseudospins,
associated to this symmetry, are observed at temperatures and voltages below
the corresponding Kondo scale. Our results demonstrate the robust formation of
entangled many-body states with no net pseudospin.Comment: 9 pages, 4 figure
De Chassemy à Ra’s al-Jinz : de la métropole à l’extrapole
Un jour du printemps 1971, quatre archéologues parisiens sans grande expérience des fouilles sur le territoire national frappèrent avec circonspection au portail de M. Rozeaux, exploitant agricole à Chassemy, dans l’Aisne. Ils souhaitaient obtenir l’autorisation de pratiquer un sondage dans un champ de betteraves pour y étudier une structure repérée en prospection aérienne. Outre l’auteur de ces lignes, orientaliste, se trouvaient là le protohistorien Jean-Paul Demoule, l’antiquisant Alain Sc..
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