2,056 research outputs found
Material and doping dependence of the nodal and anti-nodal dispersion renormalizations in single- and multi-layer cuprates
In this paper we present a review of bosonic renormalization effects on
electronic carriers observed from angle-resolved photoemission spectra in the
cuprates. We specifically discuss the viewpoint that these renormalizations
represent coupling of the electrons to the lattice, and review how the wide
range of materials dependence, such as the number of CuO layers, and the
doping dependence can be straightforwardly understood as arising due to novel
electron-phonon coupling.Comment: 9 pages and 6 figures. Submitted as a review article for Advances in
Condensed Matter Physic
Embedding Principal Component Analysis for Data Reductionin Structural Health Monitoring on Low-Cost IoT Gateways
Principal component analysis (PCA) is a powerful data reductionmethod for
Structural Health Monitoring. However, its computa-tional cost and data memory
footprint pose a significant challengewhen PCA has to run on limited capability
embedded platformsin low-cost IoT gateways. This paper presents a
memory-efficientparallel implementation of the streaming History PCA
algorithm.On our dataset, it achieves 10x compression factor and 59x
memoryreduction with less than 0.15 dB degradation in the
reconstructedsignal-to-noise ratio (RSNR) compared to standard PCA. More-over,
the algorithm benefits from parallelization on multiple cores,achieving a
maximum speedup of 4.8x on Samsung ARTIK 710
Studying the Use of Earth in Early Architecture of Southwest and Central Asia
Using case studies from Aşıklı Höyük, Çatalhöyük, Boncuklu Tarla, Göbekli Tepe (all Turkey), and Monjukli Depe (southern Turkmenistan), this study presents a framework for in-depth research on prehistoric earthen architecture in southwestern and central Asia. It demonstrates the challenges and potential for innovative and comparative studies based on interdisciplinary approaches and the use of architectural, microstratigraphic, and microarchaeological analyses. Furthermore, it sheds new light on issues related to various aspects of building continuity which is commonly recognised as a very important phenomenon in the Neolithic but could have different facets. The study attempts to discuss the reasons behind the local decisions to use and recycle specified building materials. In addition, it evaluates – in relation to particular sites – the usefulness of specific analyses for reconstruction of daily, seasonal, or annual practices. Advanced analyses of floors and fire installations, for instance, can contribute not only to the identification of indoor and outdoor surfaces but also to a better understanding of activity areas and the intensity of use within particular spaces. Variations and different combinations of mudbrick, mortar, and plaster recipes allow for insights into how earth and sediment material were used to mark collective and individual identity through the performance of a building. Recognising reused materials and features allows us to trace further the nature of prehistoric societies and local architectural dialects
Direct observation of bulk charge modulations in optimally-doped BiPbSrCaCuO
Bulk charge density modulations, recently observed in high
critical-temperature () cuprate superconductors, coexist with the
so-called pseudogap and compete with superconductivity. However, its direct
observation has been limited to a narrow doping region in the underdoped
regime. Using energy-resolved resonant x-ray scattering we have found evidence
for such bulk charge modulations, or soft collective charge modes (soft CCMs),
in optimally doped BiPbSrCaCuO
(Pb-Bi2212) around the summit of the superconducting dome with momentum
transfer reciprocal lattice units (r.l.u.) along the
Cu-O bond direction. The signal is stronger at than at
lower temperatures, thereby confirming a competition between soft CCMs and
superconductivity. These results demonstrate that soft CCMs are not constrained
to the underdoped regime, suggesting that soft CCMs appear across a large part
of the phase diagram of cuprates and are intimately entangled with
high- superconductivity.Comment: 6 pages, 3 figures, 1 tabl
Evidence for weak electronic correlations in Fe-pnictides
Using x-ray absorption and resonant inelastic x-ray scattering, charge
dynamics at and near the Fe edges is investigated in Fe pnictide materials,
and contrasted to that measured in other Fe compounds. It is shown that the XAS
and RIXS spectra for 122 and 1111 Fe pnictides are each qualitatively similar
to Fe metal. Cluster diagonalization, multiplet, and density-functional
calculations show that Coulomb correlations are much smaller than in the
cuprates, highlighting the role of Fe metallicity and strong covalency in these
materials. Best agreement with experiment is obtained using Hubbard parameters
eV and eV.Comment: 11 pages, 12 figure
Resonant Enhancement of Charge Density Wave Diffraction in the Rare-Earth Tritellurides
We performed resonant soft X-ray diffraction on known charge density wave
(CDW) compounds, rare earth tri-tellurides. Near the (3d - 4f) absorption
edge of rare earth ions, an intense diffraction peak is detected at a
wavevector identical to that of CDW state hosted on Te planes, indicating a
CDW-induced modulation on the rare earth ions. Surprisingly, the temperature
dependence of the diffraction peak intensity demonstrates an exponential
increase at low temperatures, vastly different than that of the CDW order
parameter. Assuming 4f multiplet splitting due to the CDW states,we present a
model to calculate X-ray absorption spectrum and resonant profile of the
diffraction peak, agreeing well with experimental observations. Our results
demonstrate a situation where the temperature dependence of resonant X-ray
diffraction peak intensity is not directly related to the intrinsic behavior of
the order parameter associated with the electronic order, but is dominated by
the thermal occupancy of the valence states.Comment: 7 pages, 5 figure
Doping-dependent nodal Fermi velocity in Bi-2212 revealed by high-resolution ARPES
The improved resolution of laser-based angle-resolved photoemission
spectroscopy (ARPES) allows reliable access to fine structures in the spectrum.
We present a systematic, doping-dependent study of a recently discovered
low-energy kink in the nodal dispersion of Bi2Sr2CaCu2O8+d (Bi-2212), which
demonstrates the ubiquity and robustness of this kink in underdoped Bi-2212.
The renormalization of the nodal velocity due to this kink becomes stronger
with underdoping, revealing that the nodal Fermi velocity is non-universal, in
contrast to assumed phenomenology. This is used together with laser-ARPES
measurements of the gap velocity, v2, to resolve discrepancies with thermal
conductivity measurements.Comment: Submitted to Phys. Rev. Let
Directly characterizing the relative strength and momentum dependence of electron-phonon coupling using resonant inelastic x-ray scattering
The coupling between lattice and charge degrees of freedom in condensed
matter materials is ubiquitous and can often result in interesting properties
and ordered phases, including conventional superconductivity, charge density
wave order, and metal-insulator transitions. Angle-resolved photoemission
spectroscopy and both neutron and non-resonant x-ray scattering serve as
effective probes for determining the behavior of appropriate, individual
degrees of freedom -- the electronic structure and lattice excitation, or
phonon dispersion, respectively. However, each provides less direct information
about the mutual coupling between the degrees of freedom, usual through
self-energy effects, which tend to renormalize and broaden spectral features
precisely where the coupling is strong, impacting ones ability to quantitively
characterize the coupling. Here we demonstrate that resonant inelastic x-ray
scattering, or RIXS, can be an effective tool to directly determine the
relative strength and momentum dependence of the electron-phonon coupling in
condensed matter systems. Using a diagrammatic approach for an 8-band model of
copper oxides, we study the contributions from the lowest order diagrams to the
full RIXS intensity for a realistic scattering geometry, accounting for matrix
element effects in the scattering cross-section as well as the momentum
dependence of the electron-phonon coupling vertex. A detailed examination of
these maps offers a unique perspective into the characteristics of
electron-phonon coupling, which complements both neutron and non-resonant x-ray
scattering, as well as Raman and infrared conductivity.Comment: 10 pages, 10 figure
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