180 research outputs found
Protected 0-pi states in SIsFS junctions for Josephson memory and logic
We study the peculiarities in current-phase relations (CPR) of the SIsFS
junction in the region of to transition. These CPR consist of two
independent branches corresponding to and states of the contact. We
have found that depending on the transparency of the SIs tunnel barrier the
decrease of the s-layer thickness leads to transformation of the CPR shape
going in the two possible ways: either one of the branches exists only in
discrete intervals of the phase difference or both branches are
sinusoidal but differ in the magnitude of their critical currents. We
demonstrate that the difference can be as large as under maintaining
superconductivity in the s layer. An applicability of these phenomena for
memory and logic application is discussed.Comment: 5 pages, 5 figure
Method for reliable realization of a varphi Josephson junction
We propose a method to realize a Josephson junction by combining
alternating 0 and parts (sub junctions) with an intrinsically
non-sinusoidal current-phase relation (CPR). Conditions for the realization of
the ground state are analyzed. It is shown that taking into account the
non-sinusoidal CPR for a "clean junction with a ferromagnetic (F) barrier, one
can significantly enlarge the domain (regime of suitable F-layer thicknesses)
of the ground state and make the practical realization of
Josephson junctions feasible. Such junctions may also have two different stable
solutions, such as 0 and , 0 and , or and
The effect of normal and insulating layers on 0-Ï€ transitions in Josephson junctions with a ferromagnetic barrier
Using the Usadel approach, we provide a formalism that allows us to calculate the critical current density of 21 different types of Josephson junctions (JJs) with a ferromagnetic (F) barrier and additional insulating (I) or/and normal (N) layers inserted between the F layer and superconducting (S) electrodes. In particular, we obtain that in SFS JJs, even a thin additional N layer between the S layer and F layer may noticeably change the thickness dF of the F layer at which the 0-Ï€ transitions occur. For certain values of dF, a 0-Ï€ transition can even be achieved by changing only the N layer thickness. We use our model to fit experimental data of SIFS and SINFS tunnel junctions
Record electron self-cooling in cold-electron bolometers with a hybrid superconductor-ferromagnetic nanoabsorber and traps
The Cosmic Microwave Background (CMB) radiation is the only observable that allows studying the earliest stage of the Universe. Radioastronomy instruments for CMB investigation require low working temperatures around 100 mK to get the necessary sensitivity. On-chip electron cooling of receivers is a pathway for future space missions due to problems of dilution fridges at low gravity. Here, we demonstrate experimentally that in a Cold-Electron Bolometer (CEB) a theoretical limit of electron cooling down to 65 mK from phonon temperature of 300 mK can be reached. It is possible due to effective withdrawing of hot electrons from the tunnel barrier by double stock, special traps and suppression of Andreev Joule heating in hybrid Al/Fe normal nanoabsorber
Irreversible magnetization switching at the onset of superconductivity in a superconductor ferromagnet hybrid
We demonstrate that the magnetic state of a superconducting spin valve, that is normally controlled with an external magnetic field, can also be manipulated by varying the temperature which increases the functionality and flexibility of such structures as switching elements. In this case, switching is driven by changes in the magnetostatic energy due to spontaneous Meissner screening currents forming in the superconductor below the critical temperature. Our scanning Hall probe measurements also reveal vortex-mediated pinning of the ferromagnetic domain structure due to the pinning of quantized stray fields in the adjacent superconductor. The ability to use temperature as well as magnetic field to control the local magnetisation structure raises the prospect of potential applications in magnetic memory devices.</p
Remotely induced magnetism in a normal metal using a superconducting spin-valve
Superconducting spintronics has emerged in the past decade as a promising new field that seeks to open a new dimension for nanoelectronics by utilizing the internal spin structure of the superconducting Cooper pair as a new degree of freedom. Its basic building blocks are spin-triplet Cooper pairs with equally aligned spins, which are promoted by proximity of a conventional superconductor to a ferromagnetic material with inhomogeneous macroscopic magnetization. Using low-energy muon spin-rotation experiments we find an unanticipated effect, in contradiction with the existing theoretical models of superconductivity and ferromagnetism: the appearance of a magnetization in a thin layer of a non-magnetic metal (gold), separated from a ferromagnetic double layer by a 50-nm-thick superconducting layer of Nb. The effect can be controlled either by temperature or by using a magnetic field to control the state of the remote ferromagnetic elements, and may act as a basic building block for a new generation of quantum interference devices based on the spin of a Cooper pair.</p
Spectropolarimetry of R Coronae Borealis in 1998--2003: Discovery of Transient Polarization at Maximum Brightness
We present an extended optical spectropolarimetry of R CrB from 1998 January
to 2003 September. The polarization was almost constant in the phase of maximum
brightness, being consistent with past observations. We detected, however,
temporal changes of polarization ( %) in 2001 March and August, which
were the first detection of large polarization variability in R CrB near
maximum brightness. The amplitude and the position angle of the `transient
polarization' were almost constant with wavelength in both two events. There
was a difference by about 20 degrees in the position angle between the two
events. Each event could be explained by light scattering due to short-lived
dust puff occasionally ejected off the line of sight. The flatness of the
polarization against the wavelength suggests that the scatterer is a mixture of
dust grains having various sizes. The rapid growth and fading of the transient
polarization favors the phenomenological model of dust formation near the
stellar photosphere (e.g., within two stellar radii) proposed for the time
evolution of brightness and chromospheric emission lines during deeply
declining periods, although the fading timescale can hardly be explained by a
simple dispersal of expanding dust puff with a velocity of km s
. Higher expansion velocity or some mechanism to destroy the dust grains
should be needed.Comment: 22 pages, 10 figures, accepted for publication in A
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