87 research outputs found
Cooling of suspended nanostructures with tunnel junctions
We have investigated electronic cooling of suspended nanowires with SINIS
tunnel junction coolers. The suspended samples consist of a free standing
nanowire suspended by four narrow ( 200 nm) bridges. We have compared two
different cooler designs for cooling the suspended nanowire. We demonstrate
that cooling of the nanowire is possible with a proper SINIS cooler design
Ray optics in flux avalanche propagation in superconducting films
Experimental evidence of wave properties of dendritic flux avalanches in
superconducting films is reported. Using magneto-optical imaging the
propagation of dendrites across boundaries between a bare NbN film and areas
coated by a Cu-layer was visualized, and it was found that the propagation is
refracted in full quantitative agreement with Snell's law. For the studied film
of 170 nm thickness and a 0.9 mkm thick metal layer, the refractive index was
close to n=1.4. The origin of the refraction is believed to be caused by the
dendrites propagating as an electromagnetic shock wave, similar to damped modes
considered previously for normal metals. The analogy is justified by the large
dissipation during the avalanches raising the local temperature significantly.
Additional time-resolved measurements of voltage pulses generated by segments
of the dendrites traversing an electrode confirm the consistency of the adapted
physical picture.Comment: 4 pages, 4 figure
Strain sensing with sub-micron sized Al-AlOx-Al tunnel junctions
We demonstrate a local strain sensing method for nanostructures based on
metallic Al tunnel junctions with AlOx barriers. The junctions were fabricated
on top of a thin silicon nitride membrane, which was actuated with an AFM tip
attached to a stiff cantilever. A large relative change in the tunneling
resistance in response to the applied strain (gauge factor) was observed, up to
a value 37. This facilitates local static strain variation measurements down to
~10^{-7}.Comment: 4 pages, 3 figure
Electron energy relaxation by phonons in the Kondo condensate
We have used normal metal-insulator-superconductor tunnel junctions as
thermometers at sub-Kelvin temperatures to study the electron-phonon (e-p)
interaction in thin Aluminum films doped with Manganese, as a function of
Manganese concentration. Mn in Al is known to be a Kondo impurity with
extremely high Kondo temperature 500 K, thus our results probe the
e-p coupling in the fully spin compensated, unitary limit. The temperature
dependence of the e-p interaction is consistent with the existing theory for
disordered metals, however full theory including the Kondo effect has not been
worked out yet. The strength of the interaction decreases with increasing
Manganese concentration, providing a means to improve sensitivity of detectors
and efficiency of solid state coolers
Maximizing phonon thermal conductance for ballistic membranes
At low temperatures, phonon scattering can become so weak that phonon
transport becomes ballistic. We calculate the ballistic phonon conductance G
for membranes using elasticity theory, considering the transition from three to
two dimensions. We discuss the temperature and thickness dependence and
especially concentrate on the issue of material parameters. For all membrane
thicknesses, the best conductors have, counter-intuitively, the lowest speed of
sound.Comment: 4 pages, 4 figures, proceedings to phonons 2007 conferenc
Tunneling images of a 2D electron system in a quantizing magnetic field
We have applied a scanning probe method, Subsurface Charge Accumulation (SCA)
imaging, to resolve the local structure of the interior of a semiconductor
two-dimensional electron system (2DES) in a tunneling geometry. Near magnetic
fields corresponding to integer Landau level filling, submicron scale spatial
structure in the out-of-phase component of the tunneling signal becomes
visible. In the images presented here, the structure repeats itself when the
filling factor is changed from nu=6 to nu=7. Therefore, we believe the images
reflect small modulations in the 2DES density caused by the disorder in the
sample.Comment: 2 pages, 2 color figures, submitted to LT23 proceeding
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