63,371 research outputs found
Large magnetothermal conductivity in GdBaCo_{2}O_{5+x} single crystals
To study the effects of paramagnetic spins on phonons, both the in-plane and
the c-axis heat transport of GdBaCo_{2}O_{5+x} (GBCO) single crystals are
measured at low temperature down to 0.36 K and in magnetic field up to 16 T. It
is found that the phonon heat transport is very strongly affected by the
magnetic field and nearly 5 times increase of the thermal conductivity in
several Tesla field is observed at 0.36 K. It appears that phonons are
resonantly scattered by paramagnetic spins in zero field and the application of
magnetic field removes such strong scattering, but the detailed mechanism is to
be elucidated.Comment: 5 pages, 5 figures, accepted for publication in Phys. Rev.
Intrinsic Percolative Superconductivity in Heavily Overdoped High Temperature Superconductors
Magnetic measurements on heavily overdoped ,
, and single crystals reveal
a new type magnetization hysteresis loops characterized by the vanishing of
usual central peak near zero field. Since this effect has been observed in
various systems with very different structural details, it reflects probably a
generic behavior for all high temperature superconductors. This easy
penetration of magnetic flux can be understood in the picture of percolative
superconductivity due to the inhomogeneous electronic state in heavily
overdoped regime.Comment: 4 pages, 5 figure
Giant spin-dependent photo-conductivity in GaAsN dilute nitride semiconductor
A theoretical and experimental study of the spin-dependent photoconductivity
in dilute Nitride GaAsN is presented. The non linear transport model we develop
here is based on the rate equations for electrons, holes, deep paramagnetic and
non paramagnetic centers both under CW and pulsed optical excitation. Emphasis
is given to the effect of the competition between paramagnetic centers and non
paramagnetic centers which allows us to reproduce the measured characteristics
of the spin-dependent recombination power dependence. Particular attention is
paid to the role of an external magnetic field in Voigt geometry. The
photoconductivity exhibits a Hanle-type curve whereas the spin polarization of
electrons shows two superimposed Lorentzian curves with different widths,
respectively related to the recombination of free and trapped electrons. The
model is capable of reproducing qualitatively and quantitatively the most
important features of photoluminescence and photocurrent experiments and is
helpful in providing insight on the various mechanisms involved in the electron
spin polarization and filtering in GaAsN semiconductors.Comment: 10 pages, 5 figure
Wood-Inspired Morphologically Tunable Aligned Hydrogel for High-Performance Flexible All-Solid-State Supercapacitors
Oriented microstructures are widely found in various biological systems for multiple functions. Such anisotropic structures provide low tortuosity and sufficient surface area, desirable for the design of high-performance energy storage devices. Despite significant efforts to develop supercapacitors with aligned morphology, challenges remain due to the predefined pore sizes, limited mechanical flexibility, and low mass loading. Herein, a wood-inspired flexible all-solid-state hydrogel supercapacitor is demonstrated by morphologically tuning the aligned hydrogel matrix toward high electrode-materials loading and high areal capacitance. The highly aligned matrix exhibits broad morphological tunability (47–12 µm), mechanical flexibility (0°–180° bending), and uniform polypyrrole loading up to 7 mm thick matrix. After being assembled into a solid-state supercapacitor, the areal capacitance reaches 831 mF cm−2 for the 12 µm matrix, which is 259% times of the 47 µm matrix and 403% times of nonaligned matrix. The supercapacitor also exhibits a high energy density of 73.8 µWh cm−2, power density of 4960 µW cm−2, capacitance retention of 86.5% after 1000 cycles, and bending stability of 95% after 5000 cycles. The principle to structurally design the oriented matrices for high electrode material loading opens up the possibility for advanced energy storage applications
A membrane-free flow electrolyzer operating at high current density using earth-abundant catalysts for water splitting
Electrochemical water splitting is one of the most sustainable approaches for generating hydrogen. Because of the inherent constraints associated with the architecture and materials, the conventional alkaline water electrolyzer and the emerging proton exchange membrane electrolyzer are suffering from low efficiency and high materials/operation costs, respectively. Herein, we design a membrane-free flow electrolyzer, featuring a sandwich-like architecture and a cyclic operation mode, for decoupled overall water splitting. Comprised of two physically-separated compartments with flowing H(2)-rich catholyte and O(2)-rich anolyte, the cell delivers H(2) with a purity >99.1%. Its low internal ohmic resistance, highly active yet affordable bifunctional catalysts and efficient mass transport enable the water splitting at current density of 750 mA cm(−2) biased at 2.1 V. The eletrolyzer works equally well both in deionized water and in regular tap water. This work demonstrates the opportunity of combining the advantages of different electrolyzer concepts for water splitting via cell architecture and materials design, opening pathways for sustainable hydrogen generation
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