1,300 research outputs found
Towards phase-coherent caloritronics in superconducting circuits
The emerging field of phase-coherent caloritronics (from the Latin word
"calor", i.e., heat) is based on the possibility to control heat currents using
the phase difference of the superconducting order parameter. The goal is to
design and implement thermal devices able to master energy transfer with a
degree of accuracy approaching the one reached for charge transport by
contemporary electronic components. This can be obtained by exploiting the
macroscopic quantum coherence intrinsic to superconducting condensates, which
manifests itself through the Josephson and the proximity effect. Here, we
review recent experimental results obtained in the realization of heat
interferometers and thermal rectifiers, and discuss a few proposals for exotic
non-linear phase-coherent caloritronic devices, such as thermal transistors,
solid-state memories, phase-coherent heat splitters, microwave refrigerators,
thermal engines and heat valves. Besides being very attractive from the
fundamental physics point of view, these systems are expected to have a vast
impact on many cryogenic microcircuits requiring energy management, and
possibly lay the first stone for the foundation of electronic thermal logic.Comment: 11 pages, 6 colour figure
Efficient and tunable Aharonov-Bohm quantum heat engine
We propose a quantum heat engine based on an Aharonov-Bohm interferometer in
a two-terminal geometry, and investigate its thermoelectric performances in the
linear response regime. Sizeable thermopower (up to /K) as
well as values largely exceeding unity can be achieved by simply adjusting
parameters of the setup and temperature bias across the interferometer leading
to thermal efficiency at maximum power approaching of the Carnot limit.
This is close to the optimal efficiency at maximum power achievable for a
two-terminal heat engine. Changing the magnetic flux, the asymmetry of the
structure, a side-gate bias voltage through a capacitively-coupled electrode
and the transmission of the T-junctions connecting the AB ring to the contacts
allows to finely tune the operation of the quantum heat engine. The exploration
of the parameters' space demonstrates that the high performances of the
Aharonov-Bohm two-terminal device as a quantum heat engine are stable over a
wide range of temperatures and length imbalances, promising towards
experimental realization.Comment: 5 pages, 4 figures, published versio
Phase-dependent heat transport through magnetic Josephson tunnel junctions
We present an exhaustive study of the coherent heat transport through
superconductor-ferromagnet(S-F) Josephson junctions including a spin-filter
(I) tunneling barrier. By using the quasiclassical Keldysh Green's
function technique we derive a general expression for the heat current flowing
through a S/F/I/F/S junction and analyze the dependence of the thermal
conductance on the spin-filter efficiency, the phase difference between the
superconductors and the magnetization direction of the ferromagnetic layers. In
the case of non-collinear magnetizations we show explicitly the contributions
to the heat current stemming from the singlet and triplet components of the
superconducting condensate. We also demonstrate that the magnetothermal
resistance ratio of a S/F/I/F/S heat valve can be increased by the
spin-filter effect under suitable conditions.Comment: 8 pages; 6 figure
Manifestation of a spin-splitting field in a thermally-biased Josephson junction
We investigate the behavior of a Josephson junction consisting of a
ferromagnetic insulator-superconductor (FI-S) bilayer tunnel-coupled to a
superconducting electrode. We show that the Josephson coupling in the structure
is strenghtened by the presence of the spin-splitting field induced in the FI-S
bilayer. Such strenghtening manifests itself as an increase of the critical
current with the amplitude of the exchange field. Furthermore, the effect
can be strongly enhanced if the junction is taken out of equilibrium by a
temperature bias. We propose a realistic setup to assess experimentally the
magnitude of the induced exchange field, and predict a drastic deviation of the
curve ( is the temperature) with respect to equilibrium.Comment: 4.5 pages, 3 color figure
On-Chip Cooling by Heating with Superconducting Tunnel Junctions
Heat management and refrigeration are key concepts for nanoscale devices
operating at cryogenic temperatures. The design of an on-chip mesoscopic
refrigerator that works thanks to the input heat is presented, thus realizing a
solid state implementation of the concept of cooling by heating. The system
consists of a circuit featuring a thermoelectric element based on a
ferromagnetic insulator-superconductor tunnel junction (N-FI-S) and a series of
two normal metal-superconductor tunnel junctions (SINIS). The N-FI-S element
converts the incoming heat in a thermovoltage, which is applied to the SINIS,
thereby yielding cooling. The cooler's performance is investigated as a
function of the input heat current for different bath temperatures. We show
that this system can efficiently employ the performance of SINIS refrigeration,
with a substantial cooling of the normal metal island. Its scalability and
simplicity in the design makes it a promising building block for
low-temperature on-chip energy management applications.Comment: 7 pages, 6 figure
Quantum interference hybrid spin-current injector
We propose a quantum interference spin-injector nanodevice consisting of a
superconductor-normal metal hybrid loop connected to a
superconductor-ferromagnet bilayer via a tunneling junction. We show that for
certain values of the applied voltage bias across the tunnel barrier and the
magnetic flux through the loop the spin-current can be fully polarized.
Moreover, by tuning the magnetic flux one can switch the sign of the spin
polarization. This operation can be performed at frequencies within the tens of
GHz range. We explore the nanodevice in a wide range of parameters, establish
the optimum conditions for its experimental realization and discuss its
possible applications.Comment: 4.5 pages, 4 color figure
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