199 research outputs found
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
Mesoscopic oscillations of the conductance of disordered metallic samples as a function of temperature
We show theoretically and experimentally that the conductance of small
disordered samples exhibits random oscillations as a function of temperature.
The amplitude of the oscillations decays as a power law of temperature, and
their characteristic period is of the order of the temperature itself
Seismic and mineralogical structures of the lower mantle from probabilistic tomography
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95386/1/jgrb17106.pd
Shear properties of MgO inferred using neural networks
Shear properties of mantle minerals are vital for interpreting seismic shear wave speeds and therefore inferring the composition and dynamics of a planetary interior. Shear wave speed and elastic tensor components, from which the shear modulus can be computed, are usually measured in the laboratory mimicking the Earth's (or a planet's) internal pressure and temperature conditions. A functional form that relates the shear modulus to pressure (and temperature) is fitted to the measurements and used to interpolate within and extrapolate beyond the range covered by the data. Assuming a functional form provides prior information, and the constraints on the predicted shear modulus and its uncertainties might depend largely on the assumed prior rather than the data. In the present study, we propose a data-driven approach in which we train a neural network to learn the relationship between the pressure, temperature and shear modulus from the experimental data without prescribing a functional form a priori. We present an application to MgO, but the same approach works for any other mineral if there are sufficient data to train a neural network. At low pressures, the shear modulus of MgO is well-constrained by the data. However, our results show that different experimental results are inconsistent even at room temperature, seen as multiple peaks and diverging trends in probability density functions predicted by the network. Furthermore, although an explicit finite-strain equation mostly agrees with the likelihood predicted by the neural network, there are regions where it diverges from the range given by the networks. In those regions, it is the prior assumption of the form of the equation that provides constraints on the shear modulus regardless of how the Earth behaves (or data behave). In situations where realistic uncertainties are not reported, one can become overconfident when interpreting seismic models based on those defined equations of state. In contrast, the trained neural network provides a reasonable approximation to experimental data and quantifies the uncertainty from experimental errors, interpolation uncertainty, data sparsity and inconsistencies from different experiments
Charge Pumping in Carbon Nanotubes
We demonstrate charge pumping in semiconducting carbon nanotubes by a
traveling potential wave. From the observation of pumping in the nanotube
insulating state we deduce that transport occurs by packets of charge being
carried along by the wave. By tuning the potential of a side gate, transport of
either electron or hole packets can be realized. Prospects for the realization
of nanotube based single-electron pumps are discussed
Coherent Single Charge Transport in Molecular-Scale Silicon Nanowire Transistors
We report low-temperature electrical transport studies of molecule-scale
silicon nanowires. Individual nanowires exhibit well-defined Coulomb blockade
oscillations characteristic of charge addition to a single nanostructure with
length scales up to at least 400 nm. Further studies demonstrate coherent
charge transport through discrete single particle quantum levels extending the
whole device, and show that the ground state spin configuration follows the
Lieb-Mattis theorem. In addition, depletion of the nanowires suggests that
phase coherent single-dot characteristics are accessible in a regime where
correlations are strong.Comment: 4 pages and 4 figure
Two-terminal conductance fluctuations in the integer quantum Hall regime
Motivated by recent experiments on the conductance fluctuations in mesoscopic
integr quantum Hall systems, we consider a model in which the Coulomb
interactions are incorporated into the picture of edge-state transport through
a single saddle-point. The occupancies of `classical' localised states in the
two-dimensional electron system change due to the interactions between
electrons when the gate voltage on top of the device is varied. The
electrostatic potential between the localised states and the saddle-point
causes fluctuations of the saddle-point potential and thus fluctuations of the
transmission probability of edge states. This simple model is studied
numerically and compared with the observation.Comment: 6 pages with 3 figures. To be published in Physical Review
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