60 research outputs found
SYNCHROTRON-BASED STUDIES ON CUPRATES AND MANGANITES: ELECTRONIC AND MAGNETIC CORRELATIONS
Ph.DDOCTOR OF PHILOSOPH
Essential role of liquid phase on melt-processed GdBCO single-grain superconductors
RE-Ba-Cu-O (RE denotes rare earth elements) single-grain superconductors have
garnered considerable attention owning to their ability to trap strong magnetic
field and self-stability for maglev. Here, we employed a modified melt-growth
method by adding liquid source (LS) to provide a liquid rich environment during
crystal growth. It further enables a significantly low maximum processing
temperature (Tmax) even approaching peritectic decomposition temperature. This
method was referred as the liquid source rich low Tmax (LS+LTmax) growth method
which combines the advantage of Top Seeded Infiltration Growth (TSIG) into Top
Seeded Melt-texture Growth (TSMG). The LS+LTmax method synergistically
regulates the perfect appearance and high superconducting performance in REBCO
single grains. The complementary role of liquid source and low Tmax on the
crystallization has been carefully investigated. Microstructure analysis
demonstrates that the LS+LTmax processed GdBCO single grains show clear
advantages of uniform distribution of RE3+ ions as well as RE211 particles. The
inhibition of Gd211 coarsening leads to improved pining properties. GdBCO
single-grain superconductors with diameter of 18 mm and 25 mm show maximum
trapped magnetic field of 0.746 T and 1.140 T at 77 K. These trapped fields are
significantly higher than those of conventional TSMG samples. Particularly, at
grain boundaries with reduced RE211 density superior flux pinning performance
has been observed. It indicates the existence of multiple pinning mechanisms at
these areas. The presented strategy provides essential LS+LTmax technology for
processing high performance single-grain superconductors with improved
reliability which is considered important for engineering applications
Metallic 1T Phase, 3d1 Electronic Configuration and Charge Density Wave Order in Molecular Beam Epitaxy Grown Monolayer Vanadium Ditelluride.
We present a combined experimental and theoretical study of monolayer vanadium ditelluride, VTe2, grown on highly oriented pyrolytic graphite by molecular-beam epitaxy. Using various in situ microscopic and spectroscopic techniques, including scanning tunneling microscopy/spectroscopy, synchrotron X-ray and angle-resolved photoemission, and X-ray absorption, together with theoretical analysis by density functional theory calculations, we demonstrate direct evidence of the metallic 1T phase and 3d1 electronic configuration in monolayer VTe2 that also features a (4 × 4) charge density wave order at low temperatures. In contrast to previous theoretical predictions, our element-specific characterization by X-ray magnetic circular dichroism rules out a ferromagnetic order intrinsic to the monolayer. Our findings provide essential knowledge necessary for understanding this interesting yet less explored metallic monolayer in the emerging family of van der Waals magnets
Correction to Metallic 1T Phase, 3d1 Electronic Configuration and Charge Density Wave Order in Molecular-Beam Epitaxy Grown Monolayer Vanadium Ditelluride.
It has been brought to our attention that a mistake exists in the author list. The author “Johnson Goh” in the original article should be “Kuan Eng Johnson Goh”. His primary corresponding email is [email protected]
Unravelling local spin polarization of Zhang-Rice singlet in lightly hole-doped cuprates using high-energy optical conductivity
Unrevealing local magnetic and electronic correlations in the vicinity of
charge carriers is crucial in order to understand rich physical properties in
correlated electron systems. Here, using high-energy optical conductivity (up
to 35 eV) as a function of temperature and polarization, we observe a
surprisingly strong spin polarization of the local spin singlet with enhanced
ferromagnetic correlations between Cu spins near the doped holes in lightly
hole-doped LaSrCuZnO. The changes of
the local spin polarization manifest strongly in the temperature-dependent
optical conductivity at ~7.2 eV, with an anomaly at the magnetic stripe phase
(~25 K), accompanied by anomalous spectral-weight transfer in a broad energy
range. Supported by theoretical calculations, we also assign high-energy
optical transitions and their corresponding temperature dependence,
particularly at ~2.5 ~8.7, ~9.7, ~11.3 and ~21.8 eV. Our result shows the
importance of a strong mixture of spin singlet and triplet states in hole-doped
cuprates and demonstrates a new strategy to probe local magnetic correlations
using high- energy optical conductivity in correlated electron systems.Comment: 38 pages, 11 figure
Self-passivated freestanding superconducting oxide film for flexible electronics
The integration of high-temperature superconducting YBa2Cu3O6+x (YBCO) into
flexible electronic devices has the potential to revolutionize the technology
industry. The effective preparation of high-quality flexible YBCO films
therefore plays a key role in this development. We present a novel approach for
transferring water-sensitive YBCO films onto flexible substrates without any
buffer layer. Freestanding YBCO film on a polydimethylsiloxane substrate is
extracted by etching the Sr3Al2O6 sacrificial layer from the LaAlO3 substrate.
In addition to the obtained freestanding YBCO thin film having a Tc of 89.1 K,
the freestanding YBCO thin films under inward and outward bending conditions
have Tc of 89.6 K and 88.9 K, respectively. A comprehensive characterization
involving multiple experimental techniques including high-resolution
transmission electron microscopy, scanning electron microscopy, Raman and X-ray
Absorption Spectroscopy is conducted to investigate the morphology, structural
and electronic properties of the YBCO film before and after the extraction
process where it shows the preservation of the structural and superconductive
properties of the freestanding YBCO virtually in its pristine state. Further
investigation reveals the formation of a YBCO passivated layer serves as a
protective layer which effectively preserves the inner section of the
freestanding YBCO during the etching process. This work plays a key role in
actualizing the fabrication of flexible oxide thin films and opens up new
possibilities for a diverse range of device applications involving thin-films
and low-dimensional materials.Comment: 22 pages,4 figures,references adde
Erratum:Metallic 1T phase, 3d<sup>1</sup> electronic configuration and charge density wave order in molecular-beam epitaxy grown monolayer vanadium ditelluride (ACS Nano (2019) 13:11 (12894−12900) DOI: 10.1021/acsnano.9b05349)
Evidence for metallic 1T phase, 3d1 electronic configuration and charge density wave order in molecular-beam epitaxy grown monolayer VTe2
We present a combined experimental and theoretical study of monolayer VTe2
grown on highly oriented pyrolytic graphite by molecular-beam epitaxy. Using
various in-situ microscopic and spectroscopic techniques, including scanning
tunneling microscopy/spectroscopy, synchrotron X-ray and angle-resolved
photoemission, and X-ray absorption, together with theoretical analysis by
density functional theory calculations, we demonstrate direct evidence of the
metallic 1T phase and 3d1 electronic configuration in monolayer VTe2 that also
features a (4 x 4) charge density wave order at low temperatures. In contrast
to previous theoretical predictions, our element-specific characterization by
X-ray magnetic circular dichroism rules out a ferromagnetic order intrinsic to
the monolayer. Our findings provide essential knowledge necessary for
understanding this interesting yet less explored metallic monolayer in the
emerging family of van der Waals magnets.Comment: 21 pages, 5 figure
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