2,611 research outputs found
A Microwave Josephson Refrigerator
We present a microwave quantum refrigeration principle based on the Josephson
effect. When a superconducting quantum interference device (SQUID) is pierced
by a time-dependent magnetic flux, it induces changes in the macroscopic
quantum phase and an effective finite bias voltage appears across the SQUID.
This voltage can be used to actively cool well below the lattice temperature
one of the superconducting electrodes forming the interferometer. The
achievable cooling performance combined with the simplicity and scalability
intrinsic to the structure pave the way to a number of applications in quantum
technology.Comment: 6 pages, 3 figure
Phonon deficit effect and solid state refrigerators based on superconducting tunnel junctions
Thin film devices have the advantage of being extremely compact, operate in a
continuous mode, dissipate little power, and can easily be integrated in
cryogenic detectors. Motivated by such possibilities, we investigate the phonon
deficit effect in thin film (superconductor--insulator--superconductor)
and tunnel junctions. Under certain circumstances, the phonon absorption
spectra of such tunnel junctions have spectral windows of phonon
absorption/emission. We propose to use phonon filters to select the phonon
absorbtion windows and thus to enhance the cooling effect. Membranes attached
to such tunnel junctions can be cooled in this way more effectively. We discuss
a particular superlattice design of corresponding phonon filters.Comment: 8 pages 7 figure
A survey of techniques for refrigeration, reliquefaction, and production of slush for hydrogen
Several techniques were surveyed for the refrigeration, reliquefaction and production of slush from hydrogen. The techniques included auger; bubbling helium gas; Simon desorption; the Petlier effect; Joule-Kelvin expansion using Stirling, Brayton, and Viulleumirer approaches; rotary reciprocating; a dilution refrigerator; adiabatic demagnetization of a paramagnetic salt; and adiabatic magnetization of a superconductor
Opportunities for mesoscopics in thermometry and refrigeration: Physics and applications
This review presents an overview of the thermal properties of mesoscopic
structures. The discussion is based on the concept of electron energy
distribution, and, in particular, on controlling and probing it. The
temperature of an electron gas is determined by this distribution:
refrigeration is equivalent to narrowing it, and thermometry is probing its
convolution with a function characterizing the measuring device. Temperature
exists, strictly speaking, only in quasiequilibrium in which the distribution
follows the Fermi-Dirac form. Interesting nonequilibrium deviations can occur
due to slow relaxation rates of the electrons, e.g., among themselves or with
lattice phonons. Observation and applications of nonequilibrium phenomena are
also discussed. The focus in this paper is at low temperatures, primarily below
4 K, where physical phenomena on mesoscopic scales and hybrid combinations of
various types of materials, e.g., superconductors, normal metals, insulators,
and doped semiconductors, open up a rich variety of device concepts. This
review starts with an introduction to theoretical concepts and experimental
results on thermal properties of mesoscopic structures. Then thermometry and
refrigeration are examined with an emphasis on experiments. An immediate
application of solid-state refrigeration and thermometry is in ultrasensitive
radiation detection, which is discussed in depth. This review concludes with a
summary of pertinent fabrication methods of presented devices.Comment: Close to the version published in RMP; 59 pages, 35 figure
High-temperature superconducting fault current microlimiters
High-temperature superconducting microbridges implemented with
YBa(2)Cu(3)O(7-delta) thin-films are shown to be possible fault current
limiters for microelectronic devices with some elements working at temperatures
below the superconducting critical temperature and, simultaneously, under very
low power conditions (below 1W). This is the case in the important applications
of superconductors as SQUID based electronics, and technologies for
communication or infrared detectors. In this paper it is shown that the good
thermal behavior of these microlimiters allows working in a regime where even
relatively small faults induce their transition to highly dissipative states,
dramatically increasing their limitation efficiency. The conditions for optimal
refrigeration and operation of these microlimiters are also proposed.Comment: 10 pages, 3 figures. LaTeX and EPS file
Spin caloritronics with superconductors: Enhanced thermoelectric effects, generalized Onsager response-matrix, and thermal spin currents
It has recently been proposed and experimentally demonstrated that it is
possible to generate large thermoelectric effects in ferromagnet/superconductor
structures due to a spin-dependent particle-hole asymmetry. Here, we
theoretically show that quasiparticle tunneling between two spin-split
superconductors enhances the thermoelectric response manyfold compared to when
only one such superconductor is used, generating Seebeck coefficients
( mV/K) and figures of merit () far exceeding
the best bulk thermoelectric materials, and also becomes more resilient toward
inelastic scattering processes. We present a generalized Onsager
response-matrix which takes into account spin-dependent voltage and temperature
gradients. Moreover, we show that thermally induced spin currents created in
such junctions, even in the absence of a polarized tunneling barrier, also
become largest in the case where a spin-dependent particle-hole asymmetry
exists on both sides of the barrier. We determine how these thermal spin
currents can be tuned both in magnitude and sign by several parameters,
including the external field, temperature, and the superconducting
phase-difference.Comment: 7 pages, 5 figures. v2: Added several new results, such as the
response matrix for spin-dependent biases and the evaluation of thermal spin
currents. Accepted for publication in Phys. Rev.
Adiabatic Magnetization of Superconductors as a High-Performance Cooling Mechanism
The adiabatic magnetization of a superconductor is a cooling principle
proposed in the 30s, which has never been exploited up to now. Here we present
a detailed dynamic description of the effect, computing the achievable final
temperatures as well as the process timescales for different superconductors in
various regimes. We show that, although in the experimental conditions explored
so far the method is in fact inefficient, a suitable choice of initial
temperatures and metals can lead to unexpectedly large cooling effect, even in
the presence of dissipative phenomena. Our results suggest that this principle
can be re-envisaged today as a performing refrigeration method to access the
microK regime in nanodevices.Comment: 4 pages, 3 color figure
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