1,229 research outputs found
Tunable effective g-factor in InAs nanowire quantum dots
We report tunneling spectroscopy measurements of the Zeeman spin splitting in
InAs few-electron quantum dots. The dots are formed between two InP barriers in
InAs nanowires with a wurtzite crystal structure grown by chemical beam
epitaxy. The values of the electron g-factors of the first few electrons
entering the dot are found to strongly depend on dot size and range from close
to the InAs bulk value in large dots |g^*|=13 down to |g^*|=2.3 for the
smallest dots. These findings are discussed in view of a simple model.Comment: 4 pages, 3 figure
Universal conductance fluctuations in Dirac materials in the presence of long-range disorder
We study quantum transport in Dirac materials with a single fermionic Dirac
cone (strong topological insulators and graphene in the absence of intervalley
coupling) in the presence of non-Gaussian long-range disorder. We show, by
directly calculating numerically the conductance fluctuations, that in the
limit of very large system size and disorder strength, quantum transport
becomes universal. However, a systematic deviation away from universality is
obtained for realistic system parameters. By comparing our results to existing
experimental data on 1/f noise, we suggest that many of the graphene samples
studied to date are in a non-universal crossover regime of conductance
fluctuations.Comment: 5 pages, 3 figures. Published versio
Magnetic field dependent transmission phase of a double dot system in a quantum ring
The Aharonov-Bohm effect is measured in a four-terminal open ring geometry
based on a Ga[Al]As heterostructure. Two quantum dots are embedded in the
structure, one in each of the two interfering paths. The number of electrons in
the two dots can be controlled independently. The transmission phase is
measured as electrons are added to or taken away from the individual quantum
dots. Although the measured phase shifts are in qualitative agreement with
theoretical predictions, the phase evolution exhibits unexpected dependence on
the magnetic field. For example, phase lapses are found only in certain ranges
of magnetic field.Comment: 5 pages, 4 figure
Transmission Line Impedance of Carbon Nanotube Thin Films for Chemical Sensing
We measure the resistance and frequency-dependent gate capacitance of carbon
nanotube (CNT) thin films in ambient, vacuum, and under low-pressure (10E-6
torr) analyte environments. We model the CNT film as an RC transmission line
and show that changes in the measured capacitance as a function of gate bias
and analyte pressure are consistent with changes in the transmission line
impedance due to changes in the CNT film resistivity alone; the electrostatic
gate capacitance of the CNT film does not depend on gate voltage or chemical
analyte adsorption. However, the CNT film resistance is enormously sensitive to
low pressure analyte exposure.Comment: 14 pages, 4 figure
Hooge's Constant of Carbon Nanotube Field Effect Transistors
The 1/f noise in individual semiconducting carbon nanotubes (s-CNT) in a
field effect transistor configuration has been measured in ultra-high vacuum
and following exposure to air. The amplitude of the normalized current spectral
noise density is independent of source-drain current, indicating the noise is
due to mobility rather than number fluctuations. Hooge's constant for s-CNT is
found to be 9.3 plus minus 0.4x10^-3. The magnitude of the 1/f noise is
substantially degreased by exposing the devices to air
Facile fabrication of suspended as-grown carbon nanotube devices
A simple scalable scheme is reported for fabricating suspended carbon
nanotube field effect transistors (CNT-FETs) without exposing pristine as-grown
carbon nanotubes to subsequent chemical processing. Versatility and ease of the
technique is demonstrated by controlling the density of suspended nanotubes and
reproducing devices multiple times on the same electrode set. Suspending the
carbon nanotubes results in ambipolar transport behavior with negligible
hysteresis. The Hooges constant of the suspended CNT-FETs (2.6 x 10-3) is about
20 times lower than for control CNT-FETs on SiO2 (5.6 x 10-2).Comment: 15 pages, 4 figure
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