De Gennes Superconductivity Of Metals And Alloys Pdf CreatorBy Xavier P. In and pdf 24.03.2021 at 18:32 9 min read
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- Blockade and Counterflow Supercurrent in exciton-condensate Josephson junctions
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For Entangled electron pairs superconducting spintronics, there exist two drawbacks in existing proposals of generating entangled electron pairs. One is that the two kinds of different spin entangled electron pairs mix with each other. And the other is a low efficiency of entanglement production.
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We demonstrate that perfect conversion between charged supercurrents in superconductors and neutral supercurrents in electron-hole pair condensates is possible via a new Andreev-like scattering mechanism. As a result, when two superconducting circuits are coupled through a bilayer exciton condensate, the superflow in both layers is drastically modified. Depending on the phase biases the supercurrents can be completely blocked or exhibit perfect drag.
Introduction — The terms superconductivity and superfluidity refer to dissipationless flow in charged and neutral systems, respectively. These properties provide an appealing platform for spectacular electrical effects in EC-superconductor hybrid systems in which the charged superconducting order parameter interfaces with the neutral EC order parameter.
In this Letter we demonstrate that when two superconducting circuits are coupled through a bilayer EC, the superflow in both layers is drastically altered. If the same phase bias is applied to both junctions, no Josephson current can flow through the system, a phenomenon we refer to as exciton blockade. When a phase bias is applied to only one layer, on the other hand, it induces a superdrag counterflow supercurrent of the same magnitude in the unbiased layer.
Two closely-spaced layers, assumed to host an EC, are independently contacted to four superconducting electrodes.
The electrodes in each layer are separated by a distance L much larger than the exciton coherence length, and an independent phase bias is applied to the top and bottom contacts.
In the presence of these biases, Josephson currents flow through the double layer. Because the EC is gapped, only dissipationless counterflow can contribute to the Josephson current when L is long. The EC and the dissipationless nature of its counterflow supercurrent can therefore be revealed by a purely coherent equilibrium measurement when contacted by superconducting electrodes.
Exciton blockade and superdrag — All important features of the physics we want to describe are captured by the simple one-dimensional 1D model that we now discuss in explicit detail. Later we provide arguments supporting the general validity of the conclusions we reach.
The four superconducting leads in Fig. In each layer the electron filling is controlled by a gate voltage. In contrast, the EC order parameter is taken non-vanishing in the double-layer region, i. When phase biases are applied to the four electrodes, supercurrents flow in both layers. The EC weak-link supports two contributions to the Josephson current. The quasiparticle channel contribution, in which Cooper pairs propagate by the virtual excitation of quasiparticles in the double layer, is present in ordinary weak links.
Much more interesting is the new contribution to the current which derives from the conversion of supercurrent into superfluid excitonic current. There a similar process occurs to convert the exciton current back into a Cooper-pair current. This process survives also in the long-junction limit and it leads to a number of spectacular effects, as we shall show below. In this way the problem is reduced to the evaluation of the average of the current operator over the equilibrium state of a system in which the fields satisfy these boundary conditions and the exciton order parameter 2 exhibits a space-dependent phase winding.
It follows that the EC winding wavevector q must satisfy. We find that, at zero temperature, the supercurrents in top and bottom layers flow in opposite directions. Explicitly, they exhibit a sawtooth form,. When the same phase biases are applied to the two junctions no supercurrents can flow through the EC.
When current flows in one layer due to a phase bias in that layer, a current equal in magnitude but opposite in direction flows in the other layer. This is a consequence of perfect conversion of exciton current into supercurrent. The existence of a dissipationless counterflow channel also has a spectacular impact on the temperature dependence of the critical current.
Note that the second term in square brackets in Eq. This is another important result of this Letter. Notice that this occurs even when the thermal length L t h is smaller than the length L of the junction. In the presence of the EC, Andreev processes coherently occurring in the two layers transform Cooper pairs into electron-hole pairs of the EC, which are protected from thermal decoherence by the excitonic gap.
For these reasons, the physical results obtained are not restricted to the specific 1D model discussed above. The price to pay is twofold. Secondly, the EC order parameter describing the inter-layer coupling transforms into. Energy minimization implies that the argument of the exponent proportional to x in 6 vanishes, since in the new gauge the system is effectively phase unbiased.
This fixes the winding q to be the one defined in Eq. The current-phase relationship is always of the sawtooth form. We stress that the above argument does not depend on the details of the experimental setup. In particular, it applies independently of the specific parabolic or linear energy-momentum dispersion relation of the intra-layer kinetic Hamiltonian.
Furthermore, it also holds if the contacts with the superconducting electrodes are not ideal and when their transparencies are different in the top and bottom layers. In the specific case of 2D layers with width W and highly-transparent contacts, the current is still given by Eq. The unique properties of the conversion of EC currents into charged supercurrents can be exploited for a number of possible applications.
In response to a magnetic field, an induced Josephson current I T flows in the top layer and, according to Eq. Whenever the magnetic field changes the flux by a fluxon, the currents in both layers are reversed. Current sign switches detected in the bottom layer count the fluxons present in the top layer ring. If the magnetic flux is generated by a monotonic analog input signal, the system effectively converts it into a sum of current switch pulses, i.
The system is therefore an analog-to-digital converter. A generalization to non-monotonic input signals can easily be achieved by using two double junctions. QH systems necessarily have current-carrying gapless channels localized at their edges. In a QH bar geometry the edge channels will alter the physics we discuss. Because they are gapless and atomically 2D, the field-driven carrier densities that can be achieved are much larger than in the semiconductor case.
Weaker dielectric screening and linearly dispersive conduction and valence bands help to increase both interaction and disorder energy scales. Finally, graphene bands are nearly perfectly particle-hole symmetric, guaranteeing the nearly perfect nesting between conduction and valence band Fermi surfaces which favors the coherent state. In view of this progress our predictions are likely to be within experimental reach soon. Acknowledgments — We acknowledge stimulating conversations with P.
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Blockade and Counterflow Supercurrent in exciton-condensate Josephson junctions
We demonstrate that perfect conversion between charged supercurrents in superconductors and neutral supercurrents in electron-hole pair condensates is possible via a new Andreev-like scattering mechanism. As a result, when two superconducting circuits are coupled through a bilayer exciton condensate, the superflow in both layers is drastically modified. Depending on the phase biases the supercurrents can be completely blocked or exhibit perfect drag. Introduction — The terms superconductivity and superfluidity refer to dissipationless flow in charged and neutral systems, respectively. These properties provide an appealing platform for spectacular electrical effects in EC-superconductor hybrid systems in which the charged superconducting order parameter interfaces with the neutral EC order parameter.
Magnetism pp Cite as. Superconductiviy is a quantum phenomenon. It shows up through strange physical properties which arouse curiosity but also lead to interesting applications.
For the lowest values of 1 the Legendre polynomials are given explicitly by Further symmetry relations can be obtained by combining these equations. I start with the definition and some basic properties of Legendre polynomials Pn, then. Thomas Bernhard was born in the Netherlands to Austrian parents in He was raised in Austria and studied dramatic arts at Mozarteum University in. The prose fiction of the Austrian writer Thomas Bernhard is widely regarded notably Das Kalkwerk : the tortuous descriptions of Roithamer's memoirs [the autobiographies], as in his novels, he is the creator of his the young Bernhard is seen to enjoy with some of the manual workers in Der Keller.
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