57 research outputs found
Single domain stripe order in a high-temperature superconductor
The coupling of spin, charge and lattice degrees of freedom results in the
emergence of novel states of matter across many classes of strongly correlated
electron materials. A model example is unconventional superconductivity, which
is widely believed to arise from the coupling of electrons via spin
excitations. In cuprate high-temperature superconductors, the interplay of
charge and spin degrees of freedom is also reflected in a zoo of charge and
spin-density wave orders that are intertwined with superconductivity. A key
question is whether the different types of density waves merely coexist or are
indeed directly coupled. Here we use a novel neutron diffraction technique with
superior beam-focusing that allows us to probe the subtle spin-density wave
order in the prototypical high-temperature superconductor La1.88Sr0.12CuO4
under applied uniaxial pressure to demonstrate that it is immediately coupled
with charge-density wave order. Our result shows that suitable models for
high-temperature superconductivity must equally account for charge and spin
degrees of freedom via uniaxial charge-spin stripe fluctuations
In situ uniaxial pressure cell for x-ray and neutron scattering experiments
We present an in situ uniaxial pressure device optimized for small angle x-ray and neutron scattering experiments at low-temperatures and high magnetic fields. A stepper motor generates force, which is transmitted to the sample via a rod with an integrated transducer that continuously monitors the force. The device has been designed to generate forces up to 200 N in both compressive and tensile configurations, and a feedback control allows operating the system in a continuous-pressure mode as the temperature is changed. The uniaxial pressure device can be used for various instruments and multiple cryostats through simple and exchangeable adapters. It is compatible with multiple sample holders, which can be easily changed depending on the sample properties and the desired experiment and allow rapid sample changes
Designing the stripe-ordered cuprate phase diagram through uniaxial-stress
The ability to efficiently control charge and spin in the cuprate
high-temperature superconductors is crucial for fundamental research and
underpins technological development. Here, we explore the tunability of
magnetism, superconductivity and crystal structure in the stripe phase of the
cuprate La_2-xBa_xCuO_4, with x = 0.115 and 0.135, by employing
temperature-dependent (down to 400 mK) muon-spin rotation and AC
susceptibility, as well as X-ray scattering experiments under compressive
uniaxial stress in the CuO_2 plane. A sixfold increase of the 3-dimensional
(3D) superconducting critical temperature T_c and a full recovery of the 3D
phase coherence is observed in both samples with the application of extremely
low uniaxial stress of 0.1 GPa. This finding demonstrates the removal of the
well-known 1/8-anomaly of cuprates by uniaxial stress. On the other hand, the
spin-stripe order temperature as well as the magnetic fraction at 400 mK show
only a modest decrease under stress. Moreover, the onset temperatures of 3D
superconductivity and spin-stripe order are very similar in the large stress
regime. However, a substantial decrease of the magnetic volume fraction and a
full suppression of the low-temperature tetragonal structure is found at
elevated temperatures, which is a necessary condition for the development of
the 3D superconducting phase with optimal T_c. Our results evidence a
remarkable cooperation between the long-range static spin-stripe order and the
underlying crystalline order with the three-dimensional fully coherent
superconductivity. Overall, these results suggest that the stripe- and the SC
order may have a common physical mechanism.Comment: 11 pages, 5 figures. This work builds on our earlier findings on
LBCO, arXiv:2008.01159, and substantially expands i
Weak-signal extraction enabled by deep-neural-network denoising of diffraction data
Removal or cancellation of noise has wide-spread applications for imaging and
acoustics. In every-day-life applications, denoising may even include
generative aspects which are unfaithful to the ground truth. For scientific
applications, however, denoising must reproduce the ground truth accurately.
Here, we show how data can be denoised via a deep convolutional neural network
such that weak signals appear with quantitative accuracy. In particular, we
study X-ray diffraction on crystalline materials. We demonstrate that weak
signals stemming from charge ordering, insignificant in the noisy data, become
visible and accurate in the denoised data. This success is enabled by
supervised training of a deep neural network with pairs of measured low- and
high-noise data. This way, the neural network learns about the statistical
properties of the noise. We demonstrate that using artificial noise (such as
Poisson and Gaussian) does not yield such quantitatively accurate results. Our
approach thus illustrates a practical strategy for noise filtering that can be
applied to challenging acquisition problems.Comment: 8 pages, 4 figure
Charge order above room-temperature in a prototypical kagome superconductor La(RuFe)Si
The kagome lattice is an intriguing and rich platform for discovering, tuning
and understanding the diverse phases of quantum matter, which is a necessary
premise for utilizing quantum materials in all areas of modern and future
electronics in a controlled and optimal way. The system LaRuSi was
shown to exhibit typical kagome band structure features near the Fermi energy
formed by the Ru- orbitals and the highest superconducting transition
temperature 7K among the kagome-lattice materials.
However, the effect of electronic correlations on the normal state properties
remains elusive. Here, we report the discovery of charge order in
La(RuFe)Si ( = 0, 0.01, 0.05) beyond
room-temperature. Namely, single crystal X-ray diffraction reveals charge order
with a propagation vector of (,0,0) below
400K in all three compounds. At lower temperatures, we see the
appearance of a second set of charge order peaks with a propagation vector of
(,0,0). The introduction of Fe, which is known to quickly suppress
superconductivity, does not drastically alter the onset temperature for charge
order. Instead, it broadens the scattered intensity such that diffuse
scattering appears at the same onset temperature, however does not coalesce
into sharp Bragg diffraction peaks until much lower in temperature. Our results
present the first example of a charge ordered state at or above room
temperature in the correlated kagome lattice with bulk superconductivity.Comment: 15 pages, 8 figure
Pseudogap suppression by competition with superconductivity in La-based cuprates
We carried out a comprehensive high-resolution angle-resolved photoemission spectroscopy (ARPES) study of the pseudogap interplay with superconductivity in La-based cuprates. The three systems La2−xSrxCuO4, La1.6−xNd0.4SrxCuO4, and La1.8−xEu0.2SrxCuO4 display slightly different pseudogap critical points in the temperature versus doping phase diagram. We studied the pseudogap evolution into the superconducting state for doping concentrations just below the critical point. In this setting, near optimal doping for superconductivity and in the presence of the weakest possible pseudogap, we uncover how the pseudogap is partially suppressed inside the superconducting state. This conclusion is based on the direct observation of a reduced pseudogap energy scale and re-emergence of spectral weight suppressed by the pseudogap. Altogether these observations suggest that the pseudogap phenomenon in La-based cuprates is in competition with superconductivity for antinodal spectral weight
Pseudogap Suppression by Competition with Superconductivity in La-Based Cuprates
We have carried out a comprehensive high-resolution angle-resolved
photoemission spectroscopy (ARPES) study of the pseudogap interplay with
superconductivity in La-based cuprates. The three systems
LaSrCuO, LaNdSrCuO, and
LaEuSrCuO display slightly different pseudogap
critical points in the temperature versus doping phase diagram. We have studied
the pseudogap evolution into the superconducting state for doping
concentrations just below the critical point. In this setting, near optimal
doping for superconductivity and in the presence of the weakest possible
pseudogap, we uncover how the pseudogap is partially suppressed inside the
superconducting state. This conclusion is based on the direct observation of a
reduced pseudogap energy scale and re-emergence of spectral weight suppressed
by the pseudogap. Altogether these observations suggest that the pseudogap
phenomenon in La-based cuprates is in competition with superconductivity for
anti-nodal spectral weight
The regulatory mechanisms of NG2/CSPG4 expression
Neuron-glial antigen 2 (NG2), also known as chondroitin sulphate proteoglycan 4 (CSPG4), is a surface type I transmembrane core proteoglycan that is crucially involved in cell survival, migration and angiogenesis. NG2 is frequently used as a marker for the identification and characterization of certain cell types, but little is known about the mechanisms regulating its expression. In this review, we provide evidence that the regulation of NG2 expression underlies inflammation and hypoxia and is mediated by methyltransferases, transcription factors, including Sp1, paired box (Pax) 3 and Egr-1, and the microRNA miR129-2. These regulatory factors crucially determine NG2-mediated cellular processes such as glial scar formation in the central nervous system (CNS) or tumor growth and metastasis. Therefore, they are potential targets for the establishment of novel NG2-based therapeutic strategies in the treatment of CNS injuries, cancer and other conditions of these types
Modeling and Bioinformatics Identify Responders to G-CSF in Patients With Amyotrophic Lateral Sclerosis
Objective:
Developing an integrative approach to early treatment response classification using survival modeling and bioinformatics with various biomarkers for early assessment of filgrastim (granulocyte colony stimulating factor) treatment effects in amyotrophic lateral sclerosis (ALS) patients. Filgrastim, a hematopoietic growth factor with excellent safety, routinely applied in oncology and stem cell mobilization, had shown preliminary efficacy in ALS.
Methods:
We conducted individualized long-term filgrastim treatment in 36 ALS patients. The PRO-ACT database, with outcome data from 23 international clinical ALS trials, served as historical control and mathematical reference for survival modeling. Imaging data as well as cytokine and cellular data from stem cell analysis were processed as biomarkers in a non-linear principal component analysis (NLPCA) to identify individual response.
Results:
Cox proportional hazard and matched-pair analyses revealed a significant survival benefit for filgrastim-treated patients over PRO-ACT comparators. We generated a model for survival estimation based on patients in the PRO-ACT database and then applied the model to filgrastim-treated patients. Model-identified filgrastim responders displayed less functional decline and impressively longer survival than non-responders. Multimodal biomarkers were then analyzed by PCA in the context of model-defined treatment response, allowing identification of subsequent treatment response as early as within 3 months of therapy. Strong treatment response with a median survival of 3.8 years after start of therapy was associated with younger age, increased hematopoietic stem cell mobilization, less aggressive inflammatory cytokine plasma profiles, and preserved pattern of fractional anisotropy as determined by magnetic resonance diffusion tensor imaging (DTI-MRI).
Conclusion:
Long-term filgrastim is safe, is well-tolerated, and has significant positive effects on disease progression and survival in a small cohort of ALS patients. Developing and applying a model-based biomarker response classification allows use of multimodal biomarker patterns in full potential. This can identify strong individual treatment responders (here: filgrastim) at a very early stage of therapy and may pave the way to an effective individualized treatment option
Evolution of the Toarcian (Early Jurassic) carbon-cycle and global climatic controls on local sedimentary processes (Cardigan Bay Basin, UK)
The late Early Jurassic Toarcian Stage represents the warmest interval of the Jurassic Period, with an abrupt rise in global temperatures of up to ∼7 °C in mid-latitudes at the onset of the early Toarcian Oceanic Anoxic Event (T-OAE; ∼183 Ma). The T-OAE, which has been extensively studied in marine and continental successions from both hemispheres, was marked by the widespread expansion of anoxic and euxinic waters, geographically extensive deposition of organic-rich black shales, and climatic and environmental perturbations. Climatic and environmental processes following the T-OAE are, however, poorly known, largely due to a lack of study of stratigraphically well-constrained and complete sedimentary archives. Here, we present integrated geochemical and physical proxy data (high-resolution carbon-isotope data (δ13C), bulk and molecular organic geochemistry, inorganic petrology, mineral characterisation, and major- and trace-element concentrations) from the biostratigraphically complete and expanded entire Toarcian succession in the Llanbedr (Mochras Farm) Borehole, Cardigan Bay Basin, Wales, UK. With these data, we (1) construct the first high-resolution biostratigraphically calibrated chemostratigraphic reference record for nearly the complete Toarcian Stage, (2) establish palaeoceanographic and depositional conditions in the Cardigan Bay Basin, (3) show that the T-OAE in the hemipelagic Cardigan Bay Basin was marked by the occurrence of gravity-flow deposits that were likely linked to globally enhanced sediment fluxes to continental margins and deeper marine (shelf) basins, and (4) explore how early Toarcian (tenuicostatum and serpentinum zones) siderite formation in the Cardigan Bay Basin may have been linked to low global oceanic sulphate concentrations and elevated supply of iron (Fe) from the hinterland, in response to climatically induced changes in hydrological cycling, global weathering rates and large-scale sulphide and evaporite deposition
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