1,355,067 research outputs found
Sauter-Schwinger Effect in a Bardeen-Cooper-Schrieffer Superconductor
No full textSince the 1960s a deep and surprising connection has followed the development of superconductivity and quantum field theory. The Anderson-Higgs mechanism and the similarities between the Dirac and Bogoliubov-de Gennes equations are the most intriguing examples. In this last analogy, the massive Dirac particle is identified with a quasiparticle excitation and the fermion mass energy with the superconducting gap energy. Here we follow further this parallelism and show that it predicts an outstanding phenomenon: the superconducting Sauter-Schwinger effect. As in the quantum electrodynamics Schwinger effect, where an electron-positron couple is created from the vacuum by an intense electric field, we show that an electrostatic field can generate two coherent excitations from the superconducting ground-state condensate. Differently from the dissipative thermal excitation, these form a new macroscopically coherent and dissipationless state. We discuss how the superconducting state is weakened by the creation of this kind of excitations. In addition to shedding a different light and suggesting a method for the experimental verification of the Sauter-Schwinger effect, our results pave the way to the understanding and exploitation of the interaction between superconductors and electric fields
Solitonic thermal transport in a current-biased long Josephson junction
No full textWe investigate the coherent energy and thermal transport in a temperature-biased long Josephson tunnel junction, when a Josephson vortex, i.e., a soliton, steadily drifts driven by an electric bias current. We demonstrate that thermal transport through the junction can be controlled by the bias current, since it determines the steady-state velocity of the drifting soliton. We study the effects on thermal transport of the damping affecting the soliton dynamics. In fact, a soliton locally influences the power flowing through the junction and can cause the variation of the temperature of the device. When the soliton speed increases approaching its limiting value, i.e., the Swihart velocity, we demonstrate that the soliton-induced thermal effects significantly modify. Finally, we discuss how the appropriate material selection of the superconductors forming the junction is essential, since short quasiparticle relaxation times are required to observe fast thermal effects
Adiabatic magnetization of superconductors as a high-performance cooling mechanism
No full textThe adiabatic magnetization of a superconductor is a cooling principle proposed in the 1930s, which has remained mostly unexploited so far. Here we present a detailed dynamic description of the effect, computing the achievable final temperatures as well as the process time scales 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 μK regim
Phase Coherent Josephson Thermal Router
No full textToday while the electronic current at nanoscale has been widely studied in some materials and devices, the research on the heat currents are in a embryonic state. The new field of the Coherent Caloritronics studies the manipulation and the superconducting interference phenomenons of the heat currents.
This field has given birth to some devices like the heat interferometer [3] [4] and the thermal diode [1] [2] and with this work we will do another step to the complete control of the thermal currents.
The aim of this thesis is to acquire the control over heat currents at nanoscale and to observe the effect with temperature measurement on two metallic leads (Drains).
The router, consists of a Source tunnel-coupled with a Normal metal-Insulator-Superconductor (NIS) Josephson junction to the superconducting upper branch of the heat modulator, which is coupled through a Superconductor-Insulator-Superconductor (SIS) Josephson junction to a superconducting wire,
which is coupled though a NIS junction to the Drain1; instead the lower branch is tunnel-coupled (NIS) to the Drain2. The heat modulator is a Superconducting QUantum Interference Device (SQUID).
The main effect used to get the control over the currents was theorized by Maki and Griffin [5] [6] who found an analytical expression for the heat current through Josephson junction.
The expression have two terms, the former is the usual one, which follows the thermal gradient, and the
latter depends from the phase difference of the order parameter of superconductors. The first term is always bigger than the second one in order to follow the second law of thermodynamics. We can set this phase difference with the magnetic flux through the SQUID.
In the end, the device allows to control spatially the heat current, one of the fundamental requests of thermal logic.
[1] F. Giazotto M.J. Martinez-Pérez. The josephson heat interferometer.
[2] F. Giazotto M.J. Martinez-Pérez. A quantum diffractor for thermal flux, 2014.
[3] F. Giazotto M.J. Martinez-Pérez, A. Fornieri. Rectification of electronic heat current by a hybrid thermal diode, 2015.
[4] F. Giazotto M.J. Martinez-Pérez. Efficient phase-tunable josephson thermal rectifier, 2013.
[5] A. Griffin K. Maki. Entropy transport between two superconductors by journal electron tunnelling, Phys. Rev. Lett., 1965 .
[6] B. Nathanson G.D. Guttman D.J. Bergman, E. Ben-Jacob. Phys. Rev. B, 55(3849), 1997
The electro-magnetostatic Aharonov-Bohm effect as a tool to tune the Josephson current
No full textThe electro-magnetostatic Aharonov-Bohm effect is shown to allow a full control of a Josephson junction. Both the sign and the magnitude of the supercurrent can be tuned if the junction between two superconductors is realized with a ring-shaped ballistic normal region. The implementation in a realistic set-up is discussed
Switching the sign of Josephson current through Aharonov-Bohm interferometry
No full textThe electromagnetostatic Aharonov-Bohm effect is proposed as a tool to realize a fully controllable Josephson π junction. Both the sign and the magnitude of the supercurrent can be tuned in a ring-shaped ballistic normal region coupled to superconducting electrodes by varying the magnetic flux and the electric field around suitable values. We provide a theoretical description of the system within the scattering matrix theory and discuss its implementation in a realistic setu
Phase-coherent solitonic Josephson heat oscillator
No full textSince its recent foundation, phase-coherent caloritronics has sparkled continuous interest giving rise to numerous concrete applications. This research field deals with the coherent manipulation of heat currents in mesoscopic superconducting devices by mastering the Josephson phase difference. Here, we introduce a new generation of devices for fast caloritronics able to control local heat power and temperature through manipulation of Josephson vortices, i.e., solitons. Although most salient features concerning Josephson vortices in long Josephson junctions were comprehensively hitherto explored, little is known about soliton-sustained coherent thermal transport. We demonstrate that the soliton configuration determines the temperature profile in the junction, so that, in correspondence of each magnetically induced soliton, both the flowing thermal power and the temperature significantly enhance. Finally, we thoroughly discuss a fast solitonic Josephson heat oscillator, whose frequency is in tune with the oscillation frequency of the magnetic drive. Notably, the proposed heat oscillator can effectively find application as a tunable thermal source for nanoscale heat engines and coherent thermal machines
Nonlinear Critical-Current Thermal Response of an Asymmetric Josephson Tunnel Junction
No full textWe theoretically investigate the critical current of a thermally biased superconductor-insulator-superconductor (S-I-S) Josephson junction formed by electrodes made from different Bardeen-Cooper-Schrieffer (BCS) superconductors. The response of the device is analyzed as a function of the asymmetry parameter, r=Tc1/Tc2. We highlight the appearance of jumps in the critical current of an asymmetric junction, namely, when r≠1. In fact, in such a case, at temperatures at which the BCS superconducting gaps coincide, the critical current suddenly increases or decreases. In particular, we thoroughly discuss the counterintuitive behavior of the critical current, which increases by enhancing the temperature of one lead, instead of monotonically reducing. In this case, we find that the largest jump of the critical current is obtained for moderate asymmetries, r≃3. In view of these results, the discussed behavior can be speculatively proposed as a temperature-based threshold single-photon detector with photon-counting capabilities, which operates nonlinearly in the nondissipative channel
Solitonic Josephson Thermal Transport
No full textWe explore the coherent thermal transport sustained by solitons through a long Josephson junction as a thermal gradient across the system is established. We observe that a soliton causes the heat current through the system to increase. Correspondingly, the junction warms up in conjunction with the soliton, with temperature peaks up to, e.g., approximately 56 mK for a realistic Nb-based proposed setup at a bath temperature T-bath = 4.2 K. The thermal effects on the dynamics of the soliton are also discussed. Markedly, this system inherits the topological robustness of the solitons. In view of these results, the proposed device can effectively find an application as a superconducting thermal router in which the thermal transport can be locally mastered through solitonic excitations, whose positions can be externally controlled through a magnetic field and a bias current
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