1,721,086 research outputs found
Adiabatic magnetization of superconductors as a high-performance cooling mechanism
Full text linkThe 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
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
Full text linkThe 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
Ghz superconducting single-photon detectors for dark matter search
Full text linkThe composition of dark matter is one of the puzzling topics in astrophysics. To address this issue, several experiments searching for the existence of axions have been designed, built and realized in the last twenty years. Among all the others, light shining through walls experiments promise to push the exclusion limits to lower energies. For this reason, effort is put for the development of single-photon detectors operating at frequencies <100 GHz. Here, we review recent advancements in superconducting single-photon detection. In particular, we present two sensors based on one-dimensional Josephson junctions with the capability to be in situ tuned by simple current bias: the nanoscale transition edge sensor (nano-TES) and the Josephson escape sensor (JES). These two sensors are the ideal candidates for the realization of microwave light shining through walls (LSW) experiments, since they show unprecedented frequency resolutions of about 100 GHz and 2 GHz for the nano-TES and JES, respectively
Radiation comb generation with extended Josephson junctions
No full textWe propose the implementation of a Josephson radiation comb generator based on an extended Josephson junction subject to a time dependent magnetic field. The junction critical current shows known diffraction patterns and determines the position of the critical nodes when it vanishes. When the magnetic flux passes through one of such critical nodes, the superconducting phase must undergo a π-jump to minimize the Josephson energy. Correspondingly, a voltage pulse is generated at the extremes of the junction. Under periodic driving, this allows us to produce a comb-like voltage pulses sequence. In the frequency domain, it is possible to generate up to hundreds of harmonics of the fundamental driving frequency, thus mimicking the frequency comb used in optics and metrology. We discuss several implementations through a rectangular, cylindrical, and annular junction geometries, allowing us to generate different radiation spectra and to produce an output power up to 10 pW at 50 GHz for a driving frequency of 100 MHz
Niobium Dayem nano-bridge Josephson gate-controlled transistors
No full textWe report on the realization of Nb-based all-metallic Dayem nano-bridge gate-controlled transistors (Nb-GCTs). These Josephson devices operate up to a temperature of ∼ 3 K and exhibit full suppression of the supercurrent thanks to the application of a control gate voltage. The dependence of the kinetic inductance and of the transconductance on gate voltage promises a performance already on par with so far realized metallic Josephson transistors and leads us to foresee the implementation of a superconducting digital logic based on the Nb-GCT. We conclude by showing the practical realization of a scheme implementing an all-metallic gate-tunable half-wave rectifier to be used for either superconducting electronics or photon detection applications
Impact of electrostatic fields in layered crystalline BCS superconductors
Full text linkMotivated by recent experiments reporting the suppression of the critical current in superconducting Dayem bridges by the application of strong electrostatic fields, in this paper we study the impact on the superconducting gap of charge redistribution in response to an applied electric field in thin crystalline metals. By numerically solving the BCS gap equation and the Poisson equation in a fully self-consistent way, we find that the gap becomes sensitive to the applied electric field when the size of the gap becomes an order of magnitude larger than the average level spacing of the spectrum in the normal state. In this case, the gap shows sudden rises and falls that are compatible with surface modifications of the local density of states. The effect is washed out by increasing the pairing strength toward the weak-to-moderate coupling limit or by introduction of a weak smearing in the density of states that effectively mimics a thicker sample and a weakly disordered system
Gate control of superconductivity in mesoscopic all-metallic devices
Full text linkThe possibility to tune, through the application of a control gate voltage, the supercon-ducting properties of mesoscopic devices based on Bardeen–Cooper–Schrieffer metals was recently demonstrated. Despite the extensive experimental evidence obtained on different materials and geometries, a description of the microscopic mechanism at the basis of such an unconventional effect has not been provided yet. This work discusses the technological potential of gate control of superconductivity in metallic superconductors and revises the experimental results, which provide information regarding a possible thermal origin of the effect: first, we review experiments performed on high-critical-temperature elemental superconductors (niobium and vanadium) and show how devices based on these materials can be exploited to realize basic electronic tools, such as a half-wave rectifier. Second, we discuss the origin of the gating effect by showing gate-driven suppression of the supercurrent in a suspended titanium wire and by providing a comparison between thermal and electric switching current probability distributions. Furthermore, we discuss the cold field-emission of electrons from the gate employing finite element simulations and compare the results with experimental data. In our view, the presented data provide a strong indication regarding the unlikelihood of the thermal origin of the gating effect
A gate- and flux-controlled supercurrent diode effect
No full textNon-reciprocal charge transport in supercurrent diodes (SDs) has polarized growing interest in the last few years for their potential applications in superconducting electronics (SCE). So far, SD effects have been reported in complex hybrid superconductor/semiconductor structures or metallic systems subject to moderate magnetic fields, thus showing limited potentiality for practical applications in SCE. Here, we report the design and realization of a monolithic device that shows a valuable SD effect by exploiting a Dayem bridge-based superconducting quantum interference device. Our structure allows reaching rectification efficiencies (η) up to ∼ 6 %. Moreover, the absolute value and the polarity of η can be selected on demand by the modulation of an external magnetic flux or by a gate voltage, thereby guaranteeing high versatility and improved switching speed. Furthermore, our SD operates in a wide range of temperatures up to about 70% of the superconducting critical temperature of the titanium film composing the interferometer. Our SD effect can find extended applications in SCE by operating in synergy with widespread superconducting technologies such as nanocryotrons, rapid single flux quanta, and memories
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