189 research outputs found
Superconductor spintronics: Modeling spin and charge accumulation in out-of-equilibrium NS junctions subjected to Zeeman magnetic fields
We study the spin and charge accumulation in junctions between a
superconductor and a ferromagnet or a normal metal in the presence of a Zeeman
magnetic field, when the junction is taken out of equilibrium by applying a
voltage bias. We write down the most general form for the spin and charge
current in such junctions, taking into account all spin-resolved possible
tunneling processes. We make use of these forms to calculate the spin
accumulation in NS junctions subjected to a DC bias, and to an AC bias,
sinusoidal or rectangular. We observe that in the limit of negligeable changes
on the superconducting gap, the NS dynamical conductance is insensitive to spin
imbalance. Therefore to probe the spin accumulation in the superconductor, one
needs to separate the injection and detection point, i. e. the electrical spin
detection must be non-local. We address also the effect of the spin
accumulation induced in the normal leads by driving a spin current and its
effects on the detection of the spin accumulation in the superconductor.
Finally, we investigate the out-of-equilibrium spin susceptibility of the SC,
and we show that it deviates drastically from it's equilibrium value
Atomic manipulation of the gap in BiSrCaCuO
Single atom manipulation within doped correlated electron systems would be
highly beneficial to disentangle the influence of dopants, structural defects
and crystallographic characteristics on their local electronic states.
Unfortunately, their high diffusion barrier prevents conventional manipulation
techniques. Here, we demonstrate the possibility to reversibly manipulate
select sites in the optimally doped high temperature superconductor
BiSrCaCuO using the local electric field of the tip.
We show that upon shifting individual Bi atoms at the surface, the spectral gap
associated with superconductivity is seen to reversibly change by as much as 15
meV (~5% of the total gap size). Our toy model that captures all observed
characteristics suggests the field induces lateral movement of point-like
objects that create a local pairing potential in the CuO2 plane.Comment: Published in Science, this is the originally submitted manuscript
prior to changes during the review proces
Evidence for Two Time Scales in Long SNS Junctions
We use microwave excitation to elucidate the dynamics of long superconductor
/ normal metal / superconductor Josephson junctions. By varying the excitation
frequency in the range 10 MHz - 40 GHz, we observe that the critical and
retrapping currents, deduced from the dc voltage vs. dc current characteristics
of the junction, are set by two different time scales. The critical current
increases when the ac frequency is larger than the inverse diffusion time in
the normal metal, whereas the retrapping current is strongly modified when the
excitation frequency is above the electron-phonon rate in the normal metal.
Therefore the critical and retrapping currents are associated with elastic and
inelastic scattering, respectively
High-Quality Planar high-Tc Josephson Junctions
Reproducible high-Tc Josephson junctions have been made in a rather simple
two-step process using ion irradiation. A microbridge (1 to 5 ?m wide) is
firstly designed by ion irradiating a c-axis-oriented YBa2Cu3O7-? film through
a gold mask such as the non-protected part becomes insulating. A lower Tc part
is then defined within the bridge by irradiating with a much lower fluence
through a narrow slit (20 nm) opened in a standard electronic photoresist.
These planar junctions, whose settings can be finely tuned, exhibit
reproducible and nearly ideal Josephson characteristics. This process can be
used to produce complex Josephson circuits.Comment: 4 pages, 5 figures, to be published in Applied Physics Letter
Bistability in superconducting rings containing an inhomogeneous Josephson junction
We investigate the magnetic response of a superconducting Nb ring containing
a ferromagnetic PdNi Josephson junction and a tunnel junction in parallel. A
doubling of the switching frequency is observed within certain intervals of the
external magnetic field. Assuming sinusoidal current-phase relations of both
junctions our model of a dc-SQUID embedded within a superconducting ring
explains this feature by a sequence of current reversals in the ferromagnetic
section of the junction in these field intervals. The switching anomalies are
induced by the coupling between the magnetic fluxes in the two superconducting
loops.Comment: 5 pages, 4 figure
- …