207 research outputs found
Control of Coulomb blockade in a mesoscopic Josephson junction using single electron tunneling
We study a circuit where a mesoscopic Josephson junction (JJ) is embedded in
an environment consisting of a large bias resistor and a normal metal -
superconductor tunnel junction (NIS). The effective Coulomb blockade of the JJ
can be controlled by the tunneling current through the NIS junction leading to
transistor-like characteristics. We show using phase correlation theory and
numerical simulations that substantial current gain with low current noise
( fA/) and noise temperature (
0.1 K) can be achieved. Good agreement between our numerical simulations and
experimental results is obtained.Comment: 5 pages, 4 figures, RevTE
Self heating and nonlinear current-voltage characteristics in bilayer graphene
We demonstrate by experiments and numerical simulations that the
low-temperature current-voltage characteristics in diffusive bilayer graphene
(BLG) exhibit a strong superlinearity at finite bias voltages. The
superlinearity is weakly dependent on doping and on the length of the graphene
sample. This effect can be understood as a result of Joule heating. It is
stronger in BLG than in monolayer graphene (MLG), since the conductivity of BLG
is more sensitive to temperature due to the higher density of electronic states
at the Dirac point.Comment: 9 pages, 7 figures, REVTeX 4.
Pseudo-contact angle due to superfluid vortices in He
We have investigated spreading of superfluid He on top of polished
MgF and evaporated SiO substrates. Our results show strongly varying
contact angles of 0 - 15 mrad on the evaporated layers. According to our
theoretical calculations, these contact angles can be explained by a spatially
varying distribution of vortex lines, the unpinning velocity of which is
inversely proportional to the liquid depth.Comment: 10 pages, 4 figure
Thermal shot noise in top-gated single carbon nanotube field effect transistors
The high-frequency transconductance and current noise of top-gated single
carbon nanotube transistors have been measured and used to investigate hot
electron effects in one-dimensional transistors. Results are in good agreement
with a theory of 1-dimensional nano-transistor. In particular the prediction of
a large transconductance correction to the Johnson-Nyquist thermal noise
formula is confirmed experimentally. Experiment shows that nanotube transistors
can be used as fast charge detectors for quantum coherent electronics with a
resolution of in the 0.2- band.Comment: 3 pages, 4 figure
Energy relaxation in graphene and its measurement with supercurrent
We study inelastic energy relaxation in graphene for low energies to find out
how electrons scatter with acoustic phonons and other electrons. By coupling
the graphene to superconductors, we create a strong dependence of the measured
signal, i.e.,\ critical Josephson current, on the electron population on
different energy states. Since the relative population of high- and low-energy
states is determined by the inelastic scattering processes, the critical
current becomes an effective probe for their strength. We argue that the
electron-electron interaction is the dominant relaxation method and, in our
model of two-dimensional electron-electron scattering, we find a scattering
time ps at T=500 mK, 1-2 orders of magnitude smaller than
predicted by theory.Comment: 10 pages, 13 figures submitted to Physical Review
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