49 research outputs found
Coulomb blockade thermometry using a two-dimensional array of tunnel junctions
We have measured current-voltage characteristics of two-dimensional arrays of
small tunnel junctions at temperatures from 1.5 K to 4.2 K. This corresponds to
thermal energies larger than the charging energy. We show that 2D-arrays can be
used as primary thermometers in the same way as 1D-arrays, and even have some
advantages over 1D-arrays. We have carried out Monte Carlo simulations, which
agree with our experimental results.Comment: 4 pages, 4 eps figures. Also available from Journal of Applied
Physics (http://link.aip.org/link/?jap/86/3844
Experimental demonstration of the time reversal Aharonov-Casher effect
We demonstrate the time reversal Aharonov-Casher (AC) effect in small arrays
of mesoscopic semiconductor rings. By using an electrostatic gate we can
control the spin precession rate and follow the AC phase over several
interference periods. We show that we control the precession rate in two
different gate voltage ranges; in the lower range the gate voltage dependence
is strong and linear and in the higher range the dependence in almost an order
of magnitude weaker. We also see the second harmonic of the AC interference,
oscillating with half the period. We finally map the AC phase to the spin-orbit
interaction parameter alpha and find it is consistent with Shubnikov-de Haas
analysis.Comment: 4 pages, 6 figure
A fast, primary Coulomb blockade thermometer
We have measured the third derivative of the current-voltage characteristics,
d^3I/dV^3, in a two-dimensional array of small tunnel junctions using a lock-in
amplifier. We show that this derivative is zero at a voltage which scales
linearly with the temperature and depends only on the temperature and natural
constants, thus providing a primary thermometer. We demonstrate a measurement
method which extracts the zero crossing voltage directly using a feedback
circuit. This method requires only one voltage measurement, which makes it
substantially faster than the original Coulomb blockade thermometry method.Comment: 3 pages, 4 figures. This article has been submitted to Applied
Physics Letters (http://ojps.aip.org/aplo
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
Insurance data for research in companion animals: benefits and limitations
The primary aim of this article is to review the use of animal health insurance data in the scientific literature, especially in regard to morbidity or mortality in companion animals and horses. Methods and results were compared among studies on similar health conditions from different nations and years. A further objective was to critically evaluate benefits and limitations of such databases, to suggest ways to maximize their utility and to discuss the future use of animal insurance data for research purposes. Examples of studies on morbidity, mortality and survival estimates in dogs and horses, as well as neoplasia in dogs, are discussed