34 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
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
Unconventional superconductivity in CuxBi2Se3
We report point contact measurements in high quality single crystals of
Cu0.2Bi2Se3. We observe three different kinds of spectra: (1)
Andreev-reflection spectra, from which we infer a superconducting gap size of
0.6mV; (2) spectra with a large gap which closes above Tc at about 10K; and (3)
tunneling-like spectra with zero-bias conductance peaks. These tunneling
spectra show a very large gap of ~2meV (2Delta/KTc ~ 14)
Observation of two Andreev-like energy scales in superconductor/normal-metal/superconductor junctions
Conductance spectra measurements of highly transparent ramp-type junctions
made of superconducting electrodes and non
superconducting barrier are reported. At low
temperatures below , these junctions have two prominent Andreev-like
conductance peaks with clear steps at energies and with
. No such peaks appear above . The doping dependence
at 2 K shows that both and scale roughly as .
is identified as the superconducting energy gap, while a few
scenarios are proposed as for the origin of .Comment: 19 pages, 11 figure
Proximity induced superconductivity by Bi in topological and films: Evidence for a robust zero energy bound state possibly due to Majorana Fermions
Point contact conductance measurements on topological and
films reveal a signature of superconductivity below 2-3 K. In
particular, critical current dips and a robust zero bias conductance peak are
observed. The latter suggests the presence of zero energy bound states which
could be assigned to Majorana Fermions in an unconventional topological
superconductor. We attribute these novel observations to proximity induced
local superconductivity in the films by small amounts of superconducting Bi
inclusions or segregation to the surface, and provide supportive evidence for
these effects.Comment: Accepted for publication in Physical Review B (Dec. 20, 2011), 15
figures. Version V1: arXiv:1111.3445v1 [cond-mat.supr-con] 15 Nov 201
Magnetic field dependence of the proximity-induced triplet superconductivity at ferromagnet/superconductor interfaces
Long-ranged superconductor proximity effects recently found in superconductor-ferromagnetic (S-F) systems are generally attributed to the formation of triplet-pairing correlations due to various forms of magnetic inhomogeneities at the S-F interface. In order to investigate this conjecture within a single F layer coupled to a superconductor, we performed scanning tunneling spectroscopy on bilayers of La2/3Ca1/3MnO3 (LCMO) ferromagnetic thin-films grown on high temperature superconducting films of YBa2Cu3O7- (YBCO) or Pr1.85Ca0.15CuO4 (PCCO) under various magnetic fields. We find a strong correlation between the magnitude of superconductor-related spectral features measured on the LCMO layer and the degree of magnetic inhomogeneity controlled by the external magnetic field. This corroborates theoretical predictions regarding the role played by magnetic inhomogeneities in inducing triplet-pairing at S-F interfaces.This research was supported in parts by the joint German-Israeli DIP Project (G.K. and O.M.), the United States-Israel Binational Science Foundation (O.M.), the Harry de Jur Chair in Applied Science (O.M.), the Karl Stoll Chair in advanced materials at the Technion (G.K.), the Leverhulme Trust through an International Network Grant (J.W.A.R., M.G.B. and O.M.) and the Royal Society (J.W.A.R.).This is the accepted manuscript version. The final published version is available from the publishers at http://journals.aps.org/prb/abstract/10.1103/PhysRevB.89.180506. © 2014 AP
Organizational Heterogeneity of Vertebrate Genomes
Genomes of higher eukaryotes are mosaics of segments with various structural, functional, and evolutionary properties. The availability of whole-genome sequences allows the investigation of their structure as “texts” using different statistical and computational methods. One such method, referred to as Compositional Spectra (CS) analysis, is based on scoring the occurrences of fixed-length oligonucleotides (k-mers) in the target DNA sequence. CS analysis allows generating species- or region-specific characteristics of the genome, regardless of their length and the presence of coding DNA. In this study, we consider the heterogeneity of vertebrate genomes as a joint effect of regional variation in sequence organization superimposed on the differences in nucleotide composition. We estimated compositional and organizational heterogeneity of genome and chromosome sequences separately and found that both heterogeneity types vary widely among genomes as well as among chromosomes in all investigated taxonomic groups. The high correspondence of heterogeneity scores obtained on three genome fractions, coding, repetitive, and the remaining part of the noncoding DNA (the genome dark matter - GDM) allows the assumption that CS-heterogeneity may have functional relevance to genome regulation. Of special interest for such interpretation is the fact that natural GDM sequences display the highest deviation from the corresponding reshuffled sequences
Mate choice for genetic quality when environments vary: suggestions for empirical progress
Mate choice for good-genes remains one of the most controversial evolutionary processes ever proposed. This is partly because strong directional choice should theoretically deplete the genetic variation that explains the evolution of this type of female mating preferences (the so-called lek paradox). Moreover, good-genes benefits are generally assumed to be too small to outweigh opposing direct selection on females. Here, we review recent progress in the study of mate choice for genetic quality, focussing particularly on the potential for genotype by environment interactions (GEIs) to rescue additive genetic variation for quality, and thereby resolve the lek paradox. We raise five questions that we think will stimulate empirical progress in this field, and suggest directions for research in each area: 1) How is condition-dependence affected by environmental variation? 2) How important are GEIs for maintaining additive genetic variance in condition? 3) How much do GEIs reduce the signalling value of male condition? 4) How does GEI affect the multivariate version of the lek paradox? 5) Have mating biases for high-condition males evolved because of indirect benefits