5,624 research outputs found
Interface effects in d-wave superconductor-ferromagnet junctions
Measurements of the differential conductance spectra of YBa2Cu3O7-SrRuO3 and
YBa2Cu3O7-La0.67Ca_0.33MnO3 ramp-type junctions along the node and anti-node
directions are reported. The results are consistent with a crossed Andreev
reflection effect only in YBa2Cu3O7-SrRuO3 junctions where the domain wall
width of SrRuO3 is comparable with the coherence length of YBa2Cu3O7. No such
effect was observed in the YBa2Cu3O7-La0.67Ca0.33MnO3 junctions, which is in
line with the much larger (x10) domain wall width of La0.67Ca0.33MnO3. We also
show that crossed Andreev exists only in the anti-node direction. Furthermore,
we find evidence that crossed Andreev in YBa2Cu3O7 junctions is not sensitive
to nm-scale interface defects, suggesting that the length scale of the crossed
Andreev effect is larger than the coherence length, but still smaller than the
La0.67Ca0.33MnO3's domain wall width.Comment: 5 pages, 6 figure
Quantum vortex tunneling in thin films
Cuprate films offer a unique opportunity to observe vortex tunneling effects,
due to their unusually low superfluid density and short coherence length. Here,
we measure the magnetoresistance (\textit{MR}) due to vortex motion of a long
meander line of a superconducting film made of underdoped
. At low temperatures (\textit{T}), the \textit{MR}
shows a significant deviation from Arrhenius activation. The data is consistent
with two dimensional Variable Range Hopping (VRH) of single vortices, i.e.
. The VRH temperature scale depends on the
vortex tunneling rates between pinning sites. We discuss its magnitude with
respect to estimated parameters of the meander thin film.Comment: 5 figure
A study of the ferromagnetic transition of in nanometer thick bilayers with , , Au and Cr: Signature of injected carriers in the pseudogap regime
The hypothesis regarding the existence of uncorrelated pre-formed pairs in
the pseudogap regime of superconducting is tested experimentally
using bilayers of and the itinerant ferromagnet . In
our study, we monitor the influence of on , the
ferromagnetic ordering temperature of . Here, is the temperature
of maximum dM/dT or dR/dT where M and R are the magnetization and resistance of
, respectively. We compare the results with similar measurements
carried out on bilayers of , and with
. We find that in bilayers made of underdoped 10 nm /5
nm , the values are shifted to lower temperatures by up to 6-8 K
as compared to K of the 5 nm thick reference film.
In contrast, in the other type of bilayers, which are not in the pseudogap
regime near , only a smaller shift of up to 2 K is observed. These
differences are discussed in terms of a proximity effect, where carriers from
the layer are injected into the layer and vice versa.
We suggest that correlated electrons in the pseudogap regime of
are responsible for the observed large shifts.Comment: 9 figure
Transport and spectroscopic properties of superconductor - ferromagnet - superconductor junctions of - -
Transport and Conductance spectra measurements of ramp-type junctions made of
cuprate superconducting electrodes and a manganite
ferromagnetic barrier are reported. At low
temperatures below , the conductance spectra show Andreev-like broad peaks
superposed on a tunneling-like background, and sometimes also sub-gap Andreev
resonances. The energy gap values found from fits of the data ranged
mostly between 7-10 mV. As usual, the gap features were suppressed under
magnetic fields but revealed the tunneling-like conductance background. After
field cycling to 5 or 6 T and back to 0 T, the conductance spectra were always
higher than under zero field cooling, reflecting the negative magnetoresistance
of the manganite barrier. A signature of superparamagnetism was found in the
conductance spectra of junctions with a 12 nm thick LCMO barrier. Observed
critical currents with barrier thickness of 12 nm or more, were shown to be an
artifact due to incomplete milling of one of the superconducting electrodes.Comment: 10 figure
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