157 research outputs found
Field-Induced Staggered Magnetic Order in La(2)NiO(4.133)
At low temperature the holes doped into the NiO(2) planes of La(2)NiO(4.133)
by the excess oxygen collect in diagonal stripes that separate narrow
antiferromagnetic domains. The magnetic order drops abruptly to zero at T_m =
110.5 K, but charge order remains with a period of 3a/2. We show that
application of a magnetic field in the regime T > T_m induces staggered
magnetic order of period 3a due to the net magnetic moment of the
high-temperature bond-centered stripes, together with the odd number of Ni
spins across an antiferromagnetic domain.Comment: 4 pages, Revtex, 4 epsf figs included with psfig
A 4-unit-cell superstructure in optimally doped YBa2Cu3O6.92 superconductor
Using high-energy diffraction we show that a 4-unit-cell superstructure,
q0=(1/4,0,0), along the shorter Cu-Cu bonds coexists with superconductivity in
optimally doped YBCO. A complex set of anisotropic atomic displacements on
neighboring CuO chain planes, BaO planes, and CuO2 planes, respectively,
correlated over ~3-6 unit cells gives rise to diffuse superlattice peaks. Our
observations are consistent with the presence of Ortho-IV nanodomains
containing these displacements.Comment: Corrected typo in abstrac
Probing Exfoliated Graphene Layers and Their Lithiation with Microfocused X-rays
X-ray diffraction is measured on individual bilayer and multilayer graphene single-crystals and combined with electrochemically induced lithium intercalation. In-plane Bragg peaks are observed by grazing incidence diffraction. Focusing the incident beam down to an area of about 10 ÎĽm Ă— 10 ÎĽm, individual flakes are probed by specular X-ray reflectivity. By deploying a recursive Parratt algorithm to model the experimental data, we gain access to characteristic crystallographic parameters of the samples. Notably, it is possible to directly extract the bi/multilayer graphene c-axis lattice parameter. The latter is found to increase upon lithiation, which we control using an on-chip peripheral electrochemical cell layout. These experiments demonstrate the feasibility of in situ X-ray diffraction on individual, micron-sized single crystallites of few- and bilayer two-dimensional materials
Electric-field-induced pyroelectric order and localization of the confined electrons in LaAlO3/SrTiO3 heterostructures
With infrared ellipsometry, x-ray diffraction, and electric transport
measurements we investigated the electric-field-effect on the confined
electrons at the LaAlO3/SrTiO3 interface. We obtained evidence that the
localization of the electrons at low temperature and negative gate voltage is
induced, or at least strongly enhanced, by a pyroelectric phase transition in
SrTiO3 which strongly reduces the lattice polarizability and the subsequent
Coulomb screening. In particular, we show that the charge localisation and the
polar order of SrTiO3 both develop below about 50 K and exhibit similar,
unipolar hysteresis loops as a function of the gate voltage. Our findings
suggest that the pyroelectric order also plays an important role in the quantum
phase transition at very low temperatures where superconductivity is suppressed
by an electric field.Comment: 5 pages, 4 figures, supplementary materia
Depth-dependent critical behavior in V2H
Using X-ray diffuse scattering, we investigate the critical behavior of an
order-disorder phase transition in a defective "skin-layer" of V2H. In the
skin-layer, there exist walls of dislocation lines oriented normal to the
surface. The density of dislocation lines within a wall decreases continuously
with depth. We find that, because of this inhomogeneous distribution of
defects, the transition effectively occurs at a depth-dependent local critical
temperature. A depth-dependent scaling law is proposed to describe the
corresponding critical ordering behavior.Comment: 5 pages, 4 figure
Transmission-electron-microscopy study of charge-stripe order in La(1.725)Sr(0.275)NiO(4)
We characterize the local structure and correlations of charge stripes in
La(1.725)Sr(0.275)NiO(4) using transmission-electron microscopy. We present
direct evidence that the stripe modulation is indeed one-dimensional within
each NiO(2) plane. Furthermore, we show that individual stripes tend to be
either site-centered or bond-centered, with a bias towards the former. The
spacing between stripes often fluctuates about the mean, contributing to a
certain degree of frustration of the approximate body-centered stacking along
the c-axis. These results confirm ideas inferred from previous
neutron-diffraction measurements on doped nickelates, and demonstrate that
charge-stripe order is quite different from the conventional concept of
charge-density-wave order.Comment: 5 pages, 6 figures, submitted to PR
Stripe orders in the extended Hubbard model
We study stripe orders of charge and spin density waves in the extended
Hubbard model with the nearest-neighbor Coulomb repulsion V within the mean
field approximation. We obtain V vs. T(temperature) phase diagram for the
on-site Coulomb interaction U/t=8.0 and the filling n=0.8, here t is a
nearest-neighbor transfer energy. Our result shows that the diagonal stripe
spin density wave state (SDW) is stable for small V, but for large V the most
stable state changes to a charge density wave-antiferromagnetic (CDW-AF) state.
Especially we find at low temperature and for a certain range of value of V, a
vertical stripe CDW-AF state becomes stable.Comment: LaTeX 9 pages, 17 figures, uses jpsj.st
Similarity of slow stripe fluctations between Sr-doped cuprates and oxygen-doped nickelates
Stripe fluctuations in La2NiO4.17 have been studied by 139La NMR using the
field and temperature dependence of the linewidth and relaxation rates. In the
formation process of the stripes the NMR line intensity is maximal below 230K,
starts to diminish around 140K, disappears around 50K and recovers at 4K. These
results are shown to be consistent with, but completely complementary to
neutron measurements, and to be generic for oxygen doped nickelates and
underdoped cuprates.Comment: 4 pages including 4 figure
Probing the SELEX Process with Next-Generation Sequencing
Background SELEX is an iterative process in which highly diverse synthetic nucleic acid libraries are selected over many rounds to finally identify aptamers with desired properties. However, little is understood as how binders are enriched during the selection course. Next-generation sequencing offers the opportunity to open the black box and observe a large part of the population dynamics during the selection process. Methodology We have performed a semi-automated SELEX procedure on the model target streptavidin starting with a synthetic DNA oligonucleotide library and compared results obtained by the conventional analysis via cloning and Sanger sequencing with next-generation sequencing. In order to follow the population dynamics during the selection, pools from all selection rounds were barcoded and sequenced in parallel. Conclusions High affinity aptamers can be readily identified simply by copy number enrichment in the first selection rounds. Based on our results, we suggest a new selection scheme that avoids a high number of iterative selection rounds while reducing time, PCR bias, and artifacts
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