100 research outputs found
Superconductivity in Ropes of Single-Walled Carbon Nanotubes
We report measurements on ropes of Single Walled Carbon Nanotubes (SWNT) in
low-resistance contact to non-superconducting (normal) metallic pads, at low
voltage and at temperatures down to 70 mK. In one sample, we find a two order
of magnitude resistance drop below 0.55 K, which is destroyed by a magnetic
field of the order of 1T, or by a d.c. current greater than 2.5 microA. These
features strongly suggest the existence of superconductivity in ropes of SWNT.Comment: Accepted for publication in Phys. Rev. Let
Superconductivity in Ropes of Single-Walled Carbon Nanotubes
We report measurements on ropes of Single Walled Carbon Nanotubes (SWNT) in
low-resistance contact to non-superconducting (normal) metallic pads, at low
voltage and at temperatures down to 70 mK. In one sample, we find a two order
of magnitude resistance drop below 0.55 K, which is destroyed by a magnetic
field of the order of 1T, or by a d.c. current greater than 2.5 microA. These
features strongly suggest the existence of superconductivity in ropes of SWNT.Comment: Accepted for publication in Phys. Rev. Let
Disorder, pseudospins, and backscattering in carbon nanotubes
We address the effects of disorder on the conducting properties of metal and
semiconducting carbon nanotubes. Experimentally, the mean free path is found to
be much larger in metallic tubes than in doped semiconducting tubes. We show
that this result can be understood theoretically if the disorder potential is
long-ranged. The effects of a pseudospin index that describes the internal
sublattice structure of the states lead to a suppression of scattering in
metallic tubes, but not in semiconducting tubes. This conclusion is supported
by tight-binding calculations.Comment: four page
Charge and Spin Effects in Mesoscopic Josephson Junctions
We consider the charge and spin effects in low dimensional superconducting
weak links. The first part of the review deals with the effects of
electron-electron interaction in Superconductor/Luttinger liquid/Superconductor
junctions. The experimental realization of this mesoscopic hybrid system can be
the individual single wall carbon nanotube that bridges the gap between two
bulk superconductors. The dc Josephson current through a Luttinger liquid in
the limits of perfectly and poorly transmitting junctions is evaluated. The
relationship between the Josephson effect in a long SNS junction and the
Casimir effect is discussed. In the second part of the paper we review the
recent results concerning the influence of the Zeeman and Rashba interactions
on the thermodynamical properties of ballistic S/QW/S junction fabricated in
two dimensional electron gas. It is shown that in magnetically controlled
junction there are conditions for resonant Cooper pair transition which results
in giant supercurrent through a tunnel junction and a giant magnetic response
of a multichannel SNS junction. The supercurrent induced by the joint action of
the Zeeman and Rashba interactions in 1D quantum wires connected to bulk
superconductors is predicted.Comment: 36 pages, 8 figures; minor changes in reference
Band structures of periodic carbon nanotube junctions and their symmetries analyzed by the effective mass approximation
The band structures of the periodic nanotube junctions are investigated by
the effective mass theory and the tight binding model.
The periodic junctions are constructed by introducing pairs of a pentagonal
defect and a heptagonal defect periodically in the carbon nanotube.
We treat the periodic junctions whose unit cell is composed by two kinds of
metallic nanotubes with almost same radii, the ratio of which is between 0.7
and 1 .
The discussed energy region is near the undoped Fermi level where the channel
number is kept to two, so there are two bands.
The energy bands are expressed with closed analytical forms by the effective
mass theory with some assumptions, and they coincide well with the numerical
results by the tight binding model. Differences between the two methods are
also discussed. Origin of correspondence between the band structures and the
phason pattern discussed in Phys. Rev. B {\bf 53}, 2114, is clarified. The
width of the gap and the band are in inverse proportion to the length of the
unit cell, which is the sum of the lengths measured along the tube axis in each
tube part and along 'radial' direction in the junction part. The degeneracy and
repulsion between the two bands are determined only from symmetries.Comment: RevTeX, gif fil
Supercurrents through gated superconductor-normal-metal-superconductor contacts: the Josephson-transistor
We analyze the transport through a narrow ballistic superconductor-normal-
metal-superconductor Josephson contact with non-ideal transmission at the
superconductor-normal-metal interfaces, e.g., due to insulating layers,
effective mass steps, or band misfits (SIN interfaces). The electronic spectrum
in the normal wire is determined through the combination of Andreev- and normal
reflection at the SIN interfaces. Strong normal scattering at the SIN
interfaces introduces electron- and hole-like resonances in the normal region
which show up in the quasi-particle spectrum. These resonances have strong
implications for the critical supercurrent which we find to be determined
by the lowest quasi-particle level: tuning the potential to the
points where electron- and hole-like resonances cross, we find sharp peaks in
, resulting in a transitor effect. We compare the performance of
this Resonant Josephson-Transistor (RJT) with that of a Superconducting Single
Electron Transistor (SSET).Comment: to appear in PRB, 11 pages, 9 figure
ДИАГНОСТИКА МИКРОЦИРКУЛЯЦИИ ПОВЕРХНОСТНЫХ БИОТКАНЕЙ ПРИ АРТРИТЕ НА ОСНОВЕ МЕТОДА ДИНАМИЧЕСКОГО ИЗМЕРЕНИЯ БИОСПЕКЛОВ
Results of investigation of superficial vessels of the microcirculation in the skin in the area of the right hind limb of laboratory rats before and after simulation of arthritis based on dynamic measurement method of bio-speckles are presented. The studies were performed using the authors developed hardware and software dynamic measurement of biospeckles.Приведены результаты исследования микроциркуляции в поверхностных сосудах кожи в области правой задней конечности лабораторных крыс до и после моделирования артрита на основе метода динамического измерения биоспеклов. Исследования выполнены с использованием разработанного авторами аппаратного и программного обеспечения динамического измерения биоспеклов. Установлено, что метод динамического измерения и цифровой обработки биоспеклов кожи позволяет выявить первичные изменения в микроциркуляции, происходящие на начальной стадии развития артрита, а также отслеживать дальнейшие изменения, происходящие в процессе развития заболевания. Результаты анализа спекл-изображений согласуются с общей клинической картиной течения заболевания
New metallic allotropes of planar and tubular carbon
We propose a new family of layered sp2-like carbon crystals, incorporating five-, six-, and seven-membered rings in 2D Bravais lattices. These periodic sheets can be rolled so as to generate nanotubes of different diameter and chirality. We demonstrate that these sheets and tubes are metastable and more favorable than C60, and it is also shown that their mechanical properties are similar to those of graphene. Density of states calculations of all structures revealed an intrinsic metallic behavior, independent of orientation, tube diameter, and chirality
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