1,597 research outputs found
Interference and Interaction in Multiwall Carbon Nanotubes
We report equilibrium electric resistance R and tunneling spectroscopy dI/dV
measurements obtained on single multiwall nanotubes contacted by four metallic
Au fingers from above. At low temperature quantum interference phenomena
dominate the magnetoresistance. The phase-coherence and elastic-scattering
lengths are deduced. Because the latter is of order of the circumference of the
nanotubes, transport is quasi-ballistic. This result is supported by a dI/dV
spectrum which is in good agreement with the density-of-states (DOS) due to the
one-dimensional subbands expected for a perfect single-wall tube. As a function
of temperature T the resistance increases on decreasing T and saturates at
approx. 1-10 K for all measured nanotubes. R(T) cannot be related to the
energy-dependent DOS of graphene but is mainly caused by interaction and
interference effects. On a relatively small voltage scale of order 10 meV, a
pseudogap is observed in dI/dV which agrees with Luttinger-Liquid theories for
nanotubes. Because we have used quantum diffusion based on Fermi-Liquid as well
as Luttinger-Liquid theory in trying to understand our results, a large
fraction of this paper is devoted to a careful discussion of all our results.Comment: 14 pages (twocolumn), 8 figure
Temperature dependence of Andreev spectra in a superconducting carbon nanotube quantum dot
Tunneling spectroscopy of a Nb coupled carbon nanotube quantum dot reveals
the formation of pairs of Andreev bound states (ABS) within the superconducting
gap. A weak replica of the lower ABS is found, which is generated by
quasi-particle tunnelling from the ABS to the Al tunnel probe. An inversion of
the ABS-dispersion is observed at elevated temperatures, which signals the
thermal occupation of the upper ABS. Our experimental findings are well
supported by model calculations based on the superconducting Anderson model.Comment: 6 pages, 7 figure
Sub-gap spectroscopy of thermally excited quasiparticles in a Nb contacted carbon nanotube quantum dot
We present electronic transport measurements of a single wall carbon nanotube
quantum dot coupled to Nb superconducting contacts. For temperatures comparable
to the superconducting gap peculiar transport features are observed inside the
Coulomb blockade and superconducting energy gap regions. The observed
temperature dependence can be explained in terms of sequential tunneling
processes involving thermally excited quasiparticles. In particular, these new
channels give rise to two unusual conductance peaks at zero bias in the
vicinity of the charge degeneracy point and allow to determine the degeneracy
of the ground states involved in transport. The measurements are in good
agreement with model calculations.Comment: 5 pages, 4 figure
Thermally induced subgap features in the cotunneling spectroscopy of a carbon nanotube
We report on nonlinear cotunneling spectroscopy of a carbon nanotube quantum
dot coupled to Nb superconducting contacts. Our measurements show rich subgap
features in the stability diagram which become more pronounced as the
temperature is increased. Applying a transport theory based on the
Liouville-von Neumann equation for the density matrix, we show that the
transport properties can be attributed to processes involving sequential as
well as elastic and inelastic cotunneling of quasiparticles thermally excited
across the gap. In particular, we predict thermal replicas of the elastic and
inelastic cotunneling peaks, in agreement with our experimental results.Comment: 21 pages, 9 figures, submitted to New Journal of Physic
Counting Statistics and Dephasing Transition in an Electronic Mach-Zehnder Interferometer
It was recently suggested that a novel type of phase transition may occur in
the visibility of electronic Mach-Zehnder Interferometers. Here, we present
experimental evidence for the existence of this transition. The transition is
induced by strongly non-Gaussian noise that originates from the strong coupling
of a quantum point contact to the interferometer. We provide a transparent
physical picture of the effect, by exploiting a close analogy to the
neutrino-oscillations of particle physics. In addition, our experiment
constitutes a probe of the singularity of the elusive full counting statistics
of a quantum point contact.Comment: 7 pages, 4 figures (+Supplement 8 pages, 9 figures
Edge Channel Interference Controlled by Landau Level Filling
We study the visibility of Aharonov-Bohm interference in an electronic
Mach-Zehnder interferometer (MZI) in the integer quantum Hall regime. The
visibility is controlled by the filling factor and is observed only
between and 1.0, with an unexpected maximum near .
Three energy scales extracted from the temperature and voltage dependences of
the visibility change in a very similar way with the filling factor, indicating
that the different aspects of the interference depend sensitively on the local
structure of the compressible and incompressible strips forming the quantum
Hall edge channels.Comment: 5 pages, 5 figures, final version accepted for publication in Phys.
Rev.
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