54,403 research outputs found
Thermodynamic properties of Ba1-xMxFe2As2 (M = La and K)
The specific heat of BaFeAs single crystal, electron-doped
BaLaFeAs and hole-doped BaKFeAs
polycrystals were measured. For undoped BaFeAs single crystal, a very
sharp specific heat peak was observed at 136 K. This is attributed to the
structural and antiferromagnetic transitions occurring at the same temperature.
of the electron-doped non-superconducting
BaLaFeAs also shows a small peak at 120 K, indicating a
similar but weaker structural/antiferromagnetic transition. For the hole-doped
superconducting BaKFeAs, a clear peak of was
observed at = 36 K, which is the highest peak seen at superconducting
transition for iron-based high- superconductors so far. The electronic
specific heat coefficient and Debye temperature of these
compounds were obtained from the low temperature data
Superconductivity induced by oxygen deficiency in Sr-doped LaOFeAs
We synthesized Sr-doped sample with single phase,
and systematically studied the effect of oxygen deficiency in the Sr-doped
LaOFeAs system. It is found that substitution of Sr for La indeed induces the
hole carrier evidenced by positive thermoelectric power (TEP), but no bulk
superconductivity is observed. The superconductivity can be realized by
annealing the as-grown sample in vacuum to produce the oxygen deficiency. With
increasing the oxygen deficiency, the superconducting transition temperature
() increases and maximum reaches about 26 K the same as that in
La(O,F)FeAs. TEP dramatically changes from positive to negative in the
nonsuperconducting as-grown sample to the superconducting samples with oxygen
deficiency. While is always negative for all samples (even for Sr-doped
as grown sample). It suggests that the is
still electron-type superconductor.Comment: 4 pages, 4 figure
Perceptual Zero-Tree Coding with Efficient Optimization for Embedded Platforms
This study proposes a block-edge-based perceptual zero-tree coding (PZTC) method, which is implemented with efficientoptimization on the embedded platform. PZTC combines two novel compression concepts for coding efficiency and quality:block-edge detection (BED) and the low-complexity and low-memory entropy coder (LLEC). The proposed PZTC wasimplemented as a fixed-point version and optimized on the DSP-based platform based on both the presented platformindependentand platform-dependent optimization technologies. For platform-dependent optimization, this study examinesthe fixed-point PZTC and analyzes the complexity to optimize PZTC toward achieving an optimal coding efficiency.Furthermore, hardware-based platform-dependent optimizations are presented to reduce the memory size. Theperformance, such as compression quality and efficiency, is validated by experimental results
Gate-Voltage Control of Chemical Potential and Weak Anti-localization in Bismuth Selenide
We report that BiSe thin films can be epitaxially grown on
SrTiO substrates, which allow for very large tunablity in carrier density
with a back-gate. The observed low field magnetoconductivity due to weak
anti-localization (WAL) has a very weak gate-voltage dependence unless the
electron density is reduced to very low values. Such a transition in WAL is
correlated with unusual changes in longitudinal and Hall resistivities. Our
results suggest much suppressed bulk conductivity at large negative
gate-voltages and a possible role of surface states in the WAL phenomena. This
work may pave a way for realizing three-dimensional topological insulators at
ambient conditions.Comment: 5 pages, 4 figures
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