853 research outputs found
Ultra-efficient Cooling in Ferromagnet-Superconductor Microrefrigerators
A promising scheme for electron microrefrigeration based on
ferromagnet-superconductor contacts is presented. In this setup, cooling power
densities up to 600 nW/m can be achieved leading to electronic
temperature reductions largely exceeding those obtained with existing
superconductor-normal metal tunnel contacts. Half-metallic CrO/Al bilayers
are indicated as ideal candidates for the implementation of the device.Comment: 9 pages, 3 figures, submitted to Applied Physics Letter
A normal metal tunnel-junction heat diode
We propose a low-temperature thermal rectifier consisting of a chain of three
tunnel-coupled normal metal electrodes. We show that a large heat rectification
is achievable if the thermal symmetry of the structure is broken and the
central island can release energy to the phonon bath. The performance of the
device is theoretically analyzed and, under the appropriate conditions,
temperature differences up to 200 mK between the forward and reverse
thermal bias configurations are obtained below 1 K, corresponding to a
rectification ratio 2000. The simplicity intrinsic to its
design joined with the insensitivity to magnetic fields make our device
potentially attractive as a fundamental building block in solid-state thermal
nanocircuits and in general-purpose cryogenic electronic applications requiring
energy management.Comment: 4.5 pages, 4 color figure
Fully-Balanced Heat Interferometer
A tunable and balanced heat interferometer is proposed and analyzed. The
device consists of two superconductors linked together to form a double-loop
interrupted by three Josephson junctions coupled in parallel. Both
superconductors are held at different temperatures allowing the heat currents
flowing through the structure to interfere. As we show here, thermal transport
is coherently modulated through the application of a magnetic flux.
Furthermore, such modulation can be tailored at will through the application of
an extra control flux. In addition we show that, provided a proper choice of
the system parameters, a fully balanced interferometer is obtained. The latter
means that the phase-coherent part of heat current can be controlled to the
extent of being fully suppressed. Such a device allows for a versatile
operation appearing, therefore, as an attractive key to the onset of
low-temperature coherent caloritronic circuits
Majorana bound states in hybrid 2D Josephson junctions with ferromagnetic insulators
We consider a Josephson junction consisting of superconductor/ferromagnetic
insulator (S/FI) bilayers as electrodes which proximizes a nearby 2D electron
gas. By starting from a generic Josephson hybrid planar setup we present an
exhaustive analysis of the the interplay between the superconducting and
magnetic proximity effects and the conditions under which the structure
undergoes transitions to a non-trivial topological phase. We address the 2D
bound state problem using a general transfer matrix approach that reduces the
problem to an effective 1D Hamiltonian. This allows for straightforward study
of topological properties in different symmetry classes. As an example we
consider a narrow channel coupled with multiple ferromagnetic superconducting
fingers, and discuss how the Majorana bound states can be spatially controlled
by tuning the superconducting phases. Following our approach we also show the
energy spectrum, the free energy and finally the multiterminal Josephson
current of the setup.Comment: 8 pages; 5 figure
Thermal rectification of electrons in hybrid normal metal-superconductor nanojunctions
We theoretically investigate heat transport in hybrid normal
metal-superconductor (NS) nanojunctions focusing on the effect of thermal
rectification. We show that the heat diode effect in the junction strongly
depends on the transmissivity and the nature of the NS contact. Thermal
rectification efficiency can reach up to 123% for a fully-transmissive
ballistic junction and up to 84% in diffusive NS contacts. Both values exceed
the rectification efficiency of a NIS tunnel junction (I stands for an
insulator) by a factor close to 5 and 3, respectively. Furthermore, we show
that for NS point-contacts with low transmissivity, inversion of the heat diode
effect can take place. Our results could prove useful for tailoring heat
management at the nanoscale, and for mastering thermal flux propagation in
low-temperature caloritronic nanocircuitry.Comment: 4+ pages, 3 color figure
Cold electron Josephson transistor
A superconductor-normal metal-superconductor mesoscopic Josephson junction
has been realized in which the critical current is tuned through normal current
injection using a symmetric electron cooler directly connected to the weak
link. Both enhancement of the critical current by more than a factor of two,
and supercurrent suppression have been achieved by varying the cooler bias.
Furthermore, this transistor-like device demonstrates large current gain
20) and low power dissipation
Switching the sign of Josephson current through Aharonov-Bohm interferometry
We investigate the DC Josephson effect in a superconductor-normal
metal-superconductor junction where the normal region consists of a ballistic
ring. We show that a fully controllable -junction can be realized through
the electro-magnetostatic Aharonov-Bohm effect in the ring. The sign and the
magnitude of the supercurrent can be tuned by varying the magnetic flux and the
gate voltage applied to one arm, around suitable values. The implementation in
a realistic set-up is discussed.Comment: 4 pages, 3 figure
Resonant Transport in Nb/GaAs/AlGaAs/GaAs Microstructures
Resonant transport in a hybrid semiconductor-superconductor microstructure
grown by MBE on GaAs is presented. This structure experimentally realizes the
prototype system originally proposed by de Gennes and Saint-James in 1963 in
\emph{all}-metal structures. A low temperature single peak superimposed to the
characteristic Andreev-dominated subgap conductance represents the mark of such
resonant behavior. Random matrix theory of quantum transport was employed in
order to analyze the observed magnetotransport properties and ballistic effects
were included by directly solving the Bogoliubov-de Gennes equations.Comment: 7 pages REVTeX, 4 figures, to be published by World Scientific in
Proceedings of International Symposium on Mesoscopic Superconductivity and
Spintronics (NTT R&D Center Atsugi, Japan, March 2002
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