700 research outputs found
Systematic Study of Short Range Antiferromagnetic Order and The Spin-Glass State in Lightly Doped La2-xSrxCuO4
Systematic measurements of the magnetic susceptibility were performed on
single crystals of lightly doped La2-xSrxCuO4 (x=0.03, 0.04 and 0.05). For all
samples the temperature dependence of the in-plane magnetic susceptibility
shows typical spin-glass features with spin-glass transition temperatures Tg of
6.3K, 5.5K and 5.0K for x=0.03, 0.04 and 0.05, respectively. The canonical
spin-glass order parameter extracted from the in-plane susceptibility of all
the samples follows a universal scaling curve. On the other hand, the
out-of-plane magnetic susceptibility deviates from Curie law below a
temperature Tdv, higher than Tg. Comparing with previous neutron scattering
results with an instrumental energy resolution of 0.25 meV from Wakimoto et
al., the x-dependence of Tdv is qualitatively the same as that of Tel, the
temperature below which the elastic magnetic scattering develops around (pi,
pi). Thus, a revised magnetic phase diagram in the lightly doped region of
La2-xSrxCuO4 is proposed. The Curie constants calculated from the in-plane
susceptibility are independent of the Sr concentration. On the basis of the
cluster spin-glass model, this fact might reflect an inhomogeneous distribution
of doped holes in the CuO2 plane, such as in a stripe structure.Comment: 7 pages, 6 figure
Complex regulation and multiple developmental functions of misfire, the Drosophila melanogaster ferlin gene
BACKGROUND: Ferlins are membrane proteins with multiple C2 domains and proposed functions in Ca(2+ )mediated membrane-membrane interactions in animals. Caenorhabditis elegans has two ferlin genes, one of which is required for sperm function. Mammals have several ferlin genes and mutations in the human dysferlin (DYSF) and otoferlin (OTOF) genes result in muscular dystrophy and hearing loss, respectively. Drosophila melanogaster has a single ferlin gene called misfire (mfr). A previous study showed that a mfr mutation caused male sterility because of defects in fertilization. Here we analyze the expression and structure of the mfr gene and the consequences of multiple mutations to better understand the developmental function of ferlins. RESULTS: We show that mfr is expressed in the testis and ovaries of adult flies, has tissue-specific promoters, and expresses alternatively spliced transcripts that are predicted to encode distinct protein isoforms. Studies of 11 male sterile mutations indicate that a predicted Mfr testis isoform with five C2 domains and a transmembrane (TM) domain is required for sperm plasma membrane breakdown (PMBD) and completion of sperm activation during fertilization. We demonstrate that Mfr is not required for localization of Sneaky, another membrane protein necessary for PMBD. The mfr mutations vary in their effects in females, with a subset disrupting egg patterning and causing a maternal effect delay in early embryonic development. Locations of these mutations indicate that a short Mfr protein isoform carries out ferlin activities during oogenesis. CONCLUSION: The mfr gene exhibits complex transcriptional and post-transcriptional regulation and functions in three developmental processes: sperm activation, egg patterning, and early embryogenesis. These functions are in part due to the production of protein isoforms that vary in the number of C2 domains. These findings help establish D. melanogaster as model system for understanding ferlin function and dysfunction in animals, including humans
Distinct doping dependences of the pseudogap and superconducting gap LaSrCuO cuprate superconductors
We have performed a temperature-dependent angle-integrated photoemission
study of lightly-doped to heavily-overdoped LaSrCuO and
oxygen-doped LaCuO. We found that both the magnitude * of
the (small) pseudogap and the temperature \textit{T}* at which the pseudogap is
opened increases with decreasing hole concentration, consistent with previous
studies. On the other hand, the superconducting gap was found to
remain small for decreasing hole concentration. The results can be explained if
the superconducting gap opens only on the Fermi arc around the nodal
(0,0)-() direction while the pseudogap opens around (, 0).Comment: 4 pages, 3 figure
Resonant inelastic X-ray scattering study of overdoped LaSrCuO
Resonant inelastic x-ray scattering (RIXS) at the copper K absorption edge
has been performed for heavily overdoped samples of LaSrCuO
with and 0.30. We have observed the charge transfer and
molecular-orbital excitations which exhibit resonances at incident energies of
and 8.998 keV, respectively. From a comparison with previous
results on undoped and optimally-doped samples, we determine that the
charge-transfer excitation energy increases monotonically as doping increases.
In addition, the -dependences of the RIXS spectral weight and absorption
spectrum exhibit no clear peak at keV in contrast to results in
the underdoped samples. The low-energy ( eV) continuum excitation
intensity has been studied utilizing the high energy resolution of 0.13 eV
(FWHM). A comparison of the RIXS profiles at and
indicates that the continuum intensity exists even at in the
overdoped samples, whereas it has been reported only at and
for the sample. Furthermore, we also found an additional excitation on
top of the continuum intensity at the and positions.Comment: 7 pages, 7 figure
Charge-transfer exciton in La2CuO4 probed with resonant inelastic x-ray scattering
We report a high-resolution resonant inelastic x-ray scattering study of
La2CuO4. A number of spectral features are identified that were not clearly
visible in earlier lower-resolution data. The momentum dependence of the
spectral weight and the dispersion of the lowest energy excitation across the
insulating gap have been measured in detail. The temperature dependence of the
spectral features was also examined. The observed charge transfer edge shift,
along with the low dispersion of the first charge transfer excitation are
attributed to the lattice motion being coupled to the electronic system. In
addition, we observe a dispersionless feature at 1.8 eV, which is associated
with a d-d crystal field excitation.Comment: 5 pages, 4 figure
Versatile helimagnetic phases under magnetic fields in cubic perovskite SrFeO3
A helical spin texture is of great current interest for a host of novel
spin-dependent transport phenomena. We report a rich variety of nontrivial,
helimagnetic phases in the simple cubic perovskite SrFeO3 under magnetic fields
up to 42 T. Magnetic and resistivity measurements revealed that the
proper-screw spin phase proposed for SrFeO3 can be subdivided into at least
five kinds of ordered phases. Near the multicritical point, an unconventional
anomalous Hall effect was found to show up and was interpreted as due to a
possible long-period noncoplanar spin texture with scalar spin chirality.Comment: 5 pages, 5 figures, Physical Review B in pres
Diagonal static spin correlation in the low temperature orthorhombic Pccn phase of La1.55Nd0.4Sr0.05CuO4
Elastic neutron scattering measurements have been performed on Nd, Sr
co-doped La1.55Nd0.4Sr0.05CuO4, which exhibits a structural phase transition at
Ts ~ 60K from the low temperature orthorhombic Bmab phase (labelled LTO1) to
the low temperature orthorhombic Pccn phase (labelled LTO2). At low
temperatures, well below Ts, elastic magnetic peaks are observed at the
``diagonal'' incommensurate (IC) positions (0, 1+/-0.055, 0), with modulation
direction only along the orthorhombic b-axis just as in Nd-free
La1.95Sr0.05CuO4. In the present study, the one-dimensionality of the IC
modulation, which is naturally explained by a stripe model, is clearly
demonstrated with our "single-domain" crystal. The temperature dependence of
the IC peak intensity suggests a substantial contribution from the Nd3+ spins
below ~3K. Consistent with this, the L dependence of the magnetic scattering is
accurately accounted for by a model in which the contribution of the Nd3+ spins
is explicitly included.Comment: 8 pages, 8 figure
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