121 research outputs found
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
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
Quantum dots in suspended single-wall carbon nanotubes
We present a simple technique which uses a self-aligned oxide etch to suspend individual single-wall carbon nanotubes between metallic electrodes. This enables one to compare the properties of a particular nanotube before and after suspension, as well as to study transport in suspended tubes. As an example of the utility of the technique, we study quantum dots in suspended tubes, finding that their capacitances are reduced owing to the removal of the dielectric substrate
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
Many-body effects in nonlinear optical responses of 2D layered semiconductors
We performed ultrafast degenerate pump-probe spectroscopy on monolayer WSe2
near its exciton resonance. The observed differential reflectance signals
exhibit signatures of strong many-body interactions including the
exciton-exciton interaction and free carrier induced band gap renormalization.
The exciton-exciton interaction results in a resonance blue shift which lasts
for the exciton lifetime (several ps), while the band gap renormalization
manifests as a resonance red shift with several tens ps lifetime. Our model
based on the many-body interactions for the nonlinear optical susceptibility
fits well the experimental observations. The power dependence of the spectra
shows that with the increase of pump power, the exciton population increases
linearly and then saturates, while the free carrier density increases
superlinearly, implying that exciton Auger recombination could be the origin of
these free carriers. Our model demonstrates a simple but efficient method for
quantitatively analyzing the spectra, and indicates the important role of
Coulomb interactions in nonlinear optical responses of such 2D materials
Economic Implications of Patient-Related Factors in Diabetes Care
Diabetes mellitus is a chronic disease characterized by high blood sugar levels with
serious complications, particularly if it is not adequately treated. It is increasingly
prevalent and burdensome from both a health and economic standpoint globally,
amounting to hundreds of billions of dollars in expenditure each year [1,2]. Also
increasing are the numbers and types of pharmaceutical interventions being introduced to
treat this disease. Over the next decade, numerous diabetes compounds currently in
development are expected to be commercialized, making it essential for the most robust
and accurate evidence to be available to healthcare decision-makers [3].
Approximately 90% of people with diabetes are diagnosed as Type 2 (T2D), most often
in adulthood [4]. In contrast, Type 1 diabetes (T1D) patients are commonly diagnosed as
juveniles, but live well into adulthood with effective treatment [4]. Consequently, adult
patients with diabetes, namely T2D, are responsible for most of the health and economic
burden of this disease. Therefore, much of the effort to improve outcomes and reduce
costs in diabetes concentrates on this population
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