Results 1 - 10 of 987
Results 1 - 10 of 987. Search took: 0.022 seconds
|Sort by: date | relevance|
[en] Highlights: • An adiabatic approach was developed to the theory of ac Josephson effect in mesoscopic multiterminal structures. • Different types of Shapiro-like steps were predicted and calculated analytically in a three-terminal Josephson system for the limit of small junction transparencies. • The special resonance conditions and corresponding excess of Shapiro-like steps were found out. • The possible applications of our results for the experimental observation of the Shapiro-like steps in multiterminal Josephson structures were discussed. - Abstract: The distinctive features of current–voltage characteristics are studied for mesoscopic multiterminal structures effected by external irradiation. Considering a simple model of applied dc+ac voltage, we calculate Shapiro-like steps in Josephson systems with several weakly coupled superconducting electrodes. Owing to the action of an external alternating signal, the dc current is found to be rather increased than it appears in the same multiterminal Josephson node without the radiation. The possible applications of our results for the experimental observation of the Shapiro-like steps in such Josephson structures are discussed.
[en] Low frequency noise has been studied for two types of magnetic field sensors based on magnetic tunnel junctions (MTJ). The first structure, composed of a few large MTJs, is designed for low noise applications; the second one, composed of hundreds of small MTJs, is designed for general purposes. At low frequency, both structures exhibit 1/ f noise, but with very different amplitudes. The sensors for general purposes show a much higher noise level compared to the low-noise sensors. However, the sensitivity of the low noise sensors is much smaller compared to the other ones. Thus, the limit of detection, defined as the ratio of noise and sensitivity, turns out to be roughly the same for both technologies. Using the advantages of each sensor could help to design a sensor with an improved limit of detection. (paper)
[en] We propose a phase-coherent thermal circulator based on ballistic multiterminal Josephson junctions. The breaking of time-reversal symmetry by either a magnetic flux or a superconducting phase bias allows heat to flow preferentially in one direction from one terminal to the next while heat flow in the opposite direction is suppressed. We find that our device can achieve a high circulation efficiency over a wide range of parameters and that its performance is robust with respect to the presence of disorder. We provide estimates for the expected heat currents for realistic samples.
[en] We use the Landauer–Büttiker scattering theory for electronic transport to calculate the current cross-correlations in a voltage-biased three-terminal junction with all superconducting leads. At low bias voltage, when charge transport is due to coherent multiple Andreev reflections, we find large cross-correlations compared with their normal-state value. Furthermore, depending on the parameters that characterize the properties of the scattering region between the leads, the cross-correlations can reverse their sign with respect to the case of non-interacting fermionic systems.
[en] The point contact tunnel junctions between a one-dimensional topological superconductor and single-channel quantum Hall (QH) liquids are investigated theoretically with bosonization technology and renormalization group methods. For the integer QH liquid, the universal low-energy tunneling transport is governed by the perfect Andreev reflection fixed point with quantized zero-bias conductance , which can serve as a definitive fingerprint of the existence of a Majorana fermion. For the Laughlin fractional QH liquids, its transport is governed by the perfect normal reflection fixed point with vanishing zero-bias conductance and bias-dependent conductance . Our setup is within reach of the present experimental techniques. (letter)
[en] We have developed a theory of the anomalous sub-gap currents in small gap superconducting multiple tunnelling junctions. The sub-gap current at low bath temperatures is predicted to follow a sequence of steps at 2Δ/n, where n is an integer. These steps occur because in small gap multiple tunnelling structures a quasiparticle has the chance to increase its energy successively after each tunnelling event, until eventually its energy exceeds 3Δ. At this point, it relaxes down the edge with the emission of 2Δ phonon which triggers a Cooper pair break resulting in excess sub-gap current.
[en] For decades following its introduction in 1968, the resistively and capacitively shunted junction (RCSJ) model, sometimes referred to as the Stewart–McCumber model, was successfully applied to study the dynamics of Josephson junctions embedded in a variety of superconducting circuits. In 1980 a theoretical conjecture by A.J. Leggett suggested a possible new and quite different behavior for Josephson junctions at very low temperatures. A number of experiments seemed to confirm this prediction and soon it was taken as given that junctions at tens of millikelvins should be regarded as macroscopic quantum entities. As such, they would possess discrete levels in their effective potential wells, and would escape from those wells (with the appearance of a finite junction voltage) via a macroscopic quantum tunneling process. A zeal to pursue this new physics led to a virtual abandonment of the RCSJ model in this low temperature regime. In this paper we consider a selection of essentially prototypical experiments that were carried out with the intention of confirming aspects of anticipated macroscopic quantum behavior in Josephson junctions. We address two questions: (1) How successful is the non-quantum theory (RCSJ model) in replicating those experiments? (2) How strong is the evidence that data from these same experiments does indeed reflect macroscopic quantum behavior?
[en] Spintronic magnetic sensors with the integration of magnetic materials and microstructures have been enabling people to make use of the electron spin and charge properties in many applications. The high demand for such sensors has in turn spurred the technology developments in both novel materials and their atomic-level controls. Few works, however, have been carried out and reported thus far in modeling and simulation of these spintronic magnetic sensing units based on magnetic tunnel junction (MTJ) technology. Accordingly, this paper proposes a novel modeling approach as well as an iterative simulation methodology for MTJs. A more comprehensive electrical tunneling model is established for better interpreting the conductance and current generated by the electron tunneling, and this model can also facilitate the iterative simulation of the micromagnetic dynamics. Given the improved tunneling model as well as the updated dynamic simulation, the electric characteristics of an MTJ with an external magnetic field can be conveniently computed, which provides a reliable benchmark for the future development of novel spintronic magnetic sensors. (paper)
[en] The total mass attenuation coefficients, effective atomic numbers and electron densities in some recent and newly discovered non-centrosymmetric (NCS) and iron-based superconductors have been calculated for total and partial photon interactions in the wide energy range 1 keV-100 GeV. The values of these parameters have been found to change with composition of the superconductor and change in energy whereas their behaviour has been found to be identical with all energies. The variations of these parameters with energy are shown graphically for all photon interactions. The reported data could be useful for comparing these superconductors in terms of radiation sensitivity and radiation detection. The results of this work can stimulate research for other materials and different types of newly superconductors. (author)
[en] The Josephson supercurrent through a hybrid Majorana-quantum dot-Majorana junction is investigated. We particularly analyze the effect of spin-selective coupling between the Majorana and quantum dot states, which only emerges in the topological phase and will influence the current through bent junctions and/or in the presence of magnetic fields in the quantum dot. We find that the characteristic behavior of the supercurrent through this system is quite counterintuitive, differing remarkably from the resonant tunneling, e.g. through the similar (normal phase) superconductor-quantum dot-superconductor junction. Our analysis is carried out under the influence of the full set-up parameters and for both the and periodic currents. The present study is expected to be relevant to the future exploration of applications of Majorana-nanowire circuits. (paper)