488 research outputs found
Transport phenomena in nanotube quantum dots from strong to weak confinement
We report low-temperature transport experiments on single-wall nanotubes with
metallic leads of varying contact quality, ranging from weak tunneling to
almost perfect transmission. In the weak tunneling regime, where Coulomb
blockade dominates, the nanotubes act as one-dimensional quantum dots. For
stronger coupling to the leads the conductance can be strongly enhanced by
inelastic cotunneling and the Kondo effect. For open contacts Coulomb blockade
is completely suppressed, and the low-temperature conductance remains generally
high, although we often see distinct dips in the conductance versus gate
voltage which may result from resonant backscattering.Comment: 4 pages including 3 figures, for proceedings of the Moriond meeting
200
Shell filling in closed single-wall carbon nanotube quantum dots
We observe two-fold shell filling in the spectra of closed one-dimensional
quantum dots formed in single-wall carbon nanotubes. Its signatures include a
bimodal distribution of addition energies, correlations in the excitation
spectra for different electron number, and alternation of the spins of the
added electrons. This provides a contrast with quantum dots in higher
dimensions, where such spin pairing is absent. We also see indications of an
additional fourfold periodicity indicative of K-K' subband shells. Our results
suggest that the absence of shell filling in most isolated nanotube dots
results from disorder or nonuniformity.Comment: 4 pages including 4 figure
One-dimensional transport in bundles of single-walled carbon nanotubes
We report measurements of the temperature and gate voltage dependence for
individual bundles (ropes) of single-walled nanotubes. When the conductance is
less than about e^2/h at room temperature, it is found to decrease as an
approximate power law of temperature down to the region where Coulomb blockade
sets in. The power-law exponents are consistent with those expected for
electron tunneling into a Luttinger liquid. When the conductance is greater
than e^2/h at room temperature, it changes much more slowly at high
temperatures, but eventually develops very large fluctuations as a function of
gate voltage when sufficiently cold. We discuss the interpretation of these
results in terms of transport through a Luttinger liquid.Comment: 5 pages latex including 3 figures, for proceedings of IWEPNM 99
(Kirchberg
Transport and Strong-Correlation Phenomena in Carbon Nanotube Quantum Dots in a Magnetic Field
Transport through carbon nanotube (CNT) quantum dots (QDs) in a magnetic
field is discussed. The evolution of the system from the ultraviolet to the
infrared is analyzed; the strongly correlated (SC) states arising in the
infrared are investigated. Experimental consequences of the physics are
presented -- the SC states arising at various fillings are shown to be
drastically different, with distinct signatures in the conductance and, in
particular, the noise. Besides CNT QDs, our results are also relevant to double
QD systems.Comment: 5 pages, 5 figure
Structural properties of hard disks in a narrow tube
Positional ordering of a two-dimensional fluid of hard disks is examined in
such narrow tubes where only the nearest-neighbor interactions take place.
Using the exact transfer-matrix method the transverse and longitudinal pressure
components and the correlation function are determined numerically. Fluid-solid
phase transition does not occur even in the widest tube, where the method just
loses its exactness, but the appearance of the dramatic change in the equation
of state and the longitudinal correlation function shows that the system
undergoes a structural change from a fluid to a solid-like order. The pressure
components show that the collisions are dominantly longitudinal at low
densities, while they are transverse in the vicinity of close packing density.
The transverse correlation function shows that the size of solid-like domains
grows exponentially with increasing pressure and the correlation length
diverges at close packing. It is managed to find an analytically solvable model
by expanding the contact distance up to first order. The approximate model,
which corresponds to the system of hard parallel rhombuses, behaves very
similarly to the system of hard disks.Comment: Acceped in Journal of Statistical Mechanics: Theory and Experimen
Raman spectroscopy and electrical properties of InAs nanowires with local oxidation enabled by substrate micro-trenches and laser irradiation
The thermal gradient along indium-arsenide nanowires was engineered by a
combination of fabricated micro- trenches in the supporting substrate and
focused laser irradiation. This allowed local control of thermally activated
oxidation reactions of the nanowire on the scale of the diffraction limit. The
locality of the oxidation was detected by micro-Raman mapping, and the results
were found consistent with numerical simulations of the temperature profile.
Applying the technique to nanowires in electrical devices the locally oxidized
nanowires remained conducting with a lower conductance as expected for an
effectively thinner conducting core
Heat dissipation mechanisms in hybrid superconductor-semiconductor devices revealed by Joule spectroscopy
Understanding heating and cooling mechanisms in mesoscopic
superconductor-semiconductor hybrid devices is crucial for their application in
quantum technologies. Owing to the poor thermal conductivity of typical
devices, heating effects can drive superconducting-to-normal phase transitions
even at low applied bias, observed as sharp conductance dips through the loss
of Andreev excess currents. Tracking such dips across magnetic field, cryostat
temperature, and applied microwave power, which constitutes Joule spectroscopy,
allows to uncover the underlying cooling bottlenecks in different parts of a
device. By applying this technique, we analyze heat dissipation in devices
based on full-shell InAs-Al nanowires and reveal that superconducting islands
are strongly susceptible to heating as their cooling is limited by the rather
inefficient electron-phonon coupling, as opposed to grounded superconductors
that primarily cool by quasiparticle diffusion. Our measurements indicate that
powers as low as 50-150 pW are able to fully suprpress the superconductivity of
an island. Finally, we show that applied microwaves lead to similar heating
effects as DC signals, and explore the interplay of the microwave frequency and
the effective electron-phonon relaxation time.Comment: 9 pages, 4 figure
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