763 research outputs found
GHz sandwich strip inductors based on Fe-N Films
Planar strip inductors consisting of two Fe-N films enclosing a conducting
film made of Cu, were fabricated on oxidized Si substrates. The inductors were
1mm long, 2 to 100 um wide, with layers of thickness ~0.1 um for the magnetic
films and ~0.5 um for the conductor. The soft (Hc=4-8 Oe) magnetic layers were
biased during impedance measurement by applying an external field along the
strip length thereby facilitating the transverse susceptibility configuration.
Biased strips exhibited 70 to 100% inductance enhancement at 1GHz with quality
factors Q=4.5 to 3, respectively. The magnetic contribution to the total flux
in the narrow devices was less than predicted theoretically, which was
attributed to hardening of the magnetic material at the edges of the strip,
where the deposition was close to 60 degree incidence. Test films were
fabricated on tilted substrates and found to develop a very high anisotropy (up
to 1 kOe) for deposition angles larger than 30 degrees. Optimizing the flux
closure at the strip edges and using thicker conductor layers is essential for
further improving the performance of sandwich strip inductors.Comment: 18 pages, 9 figure
Fast switching current detection at low critical currents
A pulse-and-hold technique is used to measure the switching of small critical
current Josephson junctions. This technique allows one to achieve a good binary
detection and therefore measure switching probabilities. The technique
overcomes limitations on simple square pulses and allows for the measurement of
junctions with critical currents of the order of 10nA with bias pulses of the
order of 100ns. A correlation analysis of the switching events is performed to
show how the switching probability depends on the wait time between repeated
bias pulses.Comment: Changed abstract Added reference 1
Large space structure damping design
Several FORTRAN subroutines and programs were developed which compute complex eigenvalues of a damped system using different approaches, and which rescale mode shapes to unit generalized mass and make rigid bodies orthogonal to each other. An analytical proof of a Minimum Constrained Frequency Criterion (MCFC) for a single damper is presented. A method to minimize the effect of control spill-over for large space structures is proposed. The characteristic equation of an undamped system with a generalized control law is derived using reanalysis theory. This equation can be implemented in computer programs for efficient eigenvalue analysis or control quasi synthesis. Methods to control vibrations in large space structure are reviewed and analyzed. The resulting prototype, using electromagnetic actuator, is described
Coulomb Blockade and Coherent Single-Cooper-Pair Tunneling in Single Josephson Junctions
We have measured the current-voltage characteristics of small-capacitance
single Josephson junctions at low temperatures (T < 0.04 K), where the strength
of the coupling between the single junction and the electromagnetic environment
was controlled with one-dimensional arrays of dc SQUIDs. We have clearly
observed Coulomb blockade of Cooper-pair tunneling and even a region of
negative differential resistance, when the zero-bias resistance of the SQUID
arrays is much higher than the quantum resistance h/e^2 = 26 kohm. The negative
differential resistance is evidence of coherent single-Cooper-pair tunneling in
the single Josephson junction.Comment: RevTeX, 4 pages with 6 embedded figure
Why are faculty wary of assessment?
Explanations for faculty hesitancy may be practical or principled, based on experience or hearsay, emerge from more general concerns about change, or be related to assessment in particular. Ultimately the reasons fall into four main categories: worries about the new work assessment presents, a âculture gapâ in the way assessment is presented, poor word of mouth about assessment systems, and concerns about academic freedom
Two-dimensional arrays of low capacitance tunnel junctions: general properties, phase transitions and Hall effect
We describe transport properties of two-dimensional arrays of low capacitance
tunnel junctions, such as the current voltage characteristic and its dependence
on external magnetic field and temperature. We discuss several experiments in
which the small capacitance of the junctions plays an important role. In arrays
where the junctions have a relatively large charging energy, (i.e. when they
have a low capacitance) and a high normal state resistance, the low bias
resistance increases with decreasing temperature and eventually at very low
temperature the array becomes insulating even though the electrodes in the
array are superconducting. This transition to the insulating state can be
described by thermal activation. In an intermediate region where the junction
resistance is of the order of the quantum resistance and the charging energy is
of the order of the Josephson coupling energy, the arrays can be tuned between
a superconducting and an insulating state with a magnetic field. We describe
measurements of this magnetic-field-tuned superconductor insulator transition,
and we show that the resistance data can be scaled over several orders of
magnitude. Four arrays follow the same universal function. At the transition
the transverse (Hall) resistance is found to be very small in comparison with
the longitudinal resistance. However, for magnetic field values larger than the
critical value.we observe a substantial Hall resistance. The Hall resistance of
these arrays oscillates with the applied magnetic field. features in the
magnetic field dependence of the Hall resistance can qualitatively be
correlated to features in the derivative of the longitudinal resistance,
similar to what is found in the quantum Hall effect.Comment: 29 pages, 16 eps figures, uses aipproc.sty and epsfig.sty,
contribution to Euroschool on "Superconductivity in Networks and Mesoscopic
Systems", held in Siena, Italy (8-20 september 1997
Spin flip scattering at Al surfaces
Non-local measurements are performed on a multi terminal device to
determine the spin diffusion length and in combination with resistivity
measurements also the spin relaxation time in Al films. By varying the
thickness of Al we determine the contribution to spin relaxation from surface
scattering. From the temperature dependence of the spin diffusion length it is
established that the spin relaxation is impurity dominated at low temperature.
A comparison of the spin and momentum relaxation lengths for different
thicknesses reveals that the spin flip scattering at the surfaces is weak
compared to that within the bulk of the Al films.Comment: 11 pages, 5 figure
Enhanced spin accumulation in a superconductor
A lateral array of ferromagnetic tunnel junctions is used to inject and
detect non-equilibrium quasi-particle spin distribution in a superconducting
strip made of Al. The strip width and thickness is kept below the quasi
particle spin diffusion length in Al. Non-local measurements in multiple
parallel and antiparallel magnetic states of the detectors are used to in-situ
determine the quasi-particle spin diffusion length. A very large increase in
the spin accumulation in the superconducting state compared to that in the
normal state is observed and is attributed to a diminishing of the
quasi-particle population by opening of the gap below the transition
temperature.Comment: 6 pages, 4 figures; accepted for publication in Journal of Applied
Physic
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