2,101 research outputs found
Multiple Superconducting Gaps, Anisotropic Spin Fluctuations and Spin-Orbit Coupling in Iron-Pnictides
This article reviews the NMR and NQR studies on iron-based high-temperature
superconductors by the IOP/Okayama group. It was found that the electron pairs
in the superconducting state are in the spin-singlet state with multiple
fully-opened energy gaps. The antiferromagnetic spin fluctuations in the normal
state are found to be closely correlated with the superconductivity. Also the
antiferromagnetic spin fluctuations are anisotropic in the spin space, which is
different from the case in copper oxide superconductors. This anisotropy
originates from the spin-orbit coupling and is an important reflection of the
multiple-bands nature of this new class of superconductors.Comment: 20 pages, 16 figure
On the uniqueness of the non-minimal matter coupling in massive gravity and bigravity
In de Rham-Gabadadze-Tolley (dRGT) massive gravity and bigravity, a
non-minimal matter coupling involving both metrics generically re-introduces
the Boulware--Deser (BD) ghost. A non-minimal matter coupling via a simple, yet
specific composite metric has been proposed, which eliminates the BD ghost
below the strong coupling scale. Working explicitly in the metric formulation
and for arbitrary spacetime dimensions, we show that this composite metric is
the unique consistent non-minimal matter coupling below the strong coupling
scale, which emerges out of two diagnostics, namely, absence of Ostrogradski
ghosts in the decoupling limit and absence of the BD ghost from matter quantum
loop corrections.Comment: v2: references added, matches accepted version in Physics Letters B
v1: 6 pages, two-colum
Nodeless energy gaps of single-crystalline Ba0.68K0.32Fe2As2 as seen via 75As NMR
We report As nuclear magnetic resonance studies on a very clean
hole-doped single-crystal BaKFeAs ( K). The spin-lattice relaxation rate shows an exponential
decrease below down to ,
which indicates a fully opened energy gap. From the ratio , where and denote the crystal directions, we find that the
antiferromagnetic spin fluctuation is anisotropic in the spin space above
. The anisotropy decreases below and disappears at . We argue that the anisotropy stems from spin-orbit coupling
whose effect vanishes when spin-singlet electron pairs form with a nodeless
gap.Comment: 10 pages, 6 figure
Extraction of Plumes in Turbulent Thermal Convection
We present a scheme to extract information about plumes, a prominent coherent
structure in turbulent thermal convection, from simultaneous local velocity and
temperature measurements. Using this scheme, we study the temperature
dependence of the plume velocity and understand the results using the equations
of motion. We further obtain the average local heat flux in the vertical
direction at the cell center. Our result shows that heat is not mainly
transported through the central region but instead through the regions near the
sidewalls of the convection cell.Comment: 4 pages, 4 figures, submitted to Physical Review Letter
Possible Way to Synthesize Superheavy Element Z=117
Within the framework of the dinuclear system model, the production of
superheavy element Z=117 in possible projectile-target combinations is analyzed
systematically. The calculated results show that the production cross sections
are strongly dependent on the reaction systems. Optimal combinations,
corresponding excitation energies and evaporation channels are proposed in this
letter, such as the isotopes ^{248,249}Bk in ^{48}Ca induced reactions in 3n
evaporation channels and the reactions ^{45}Sc+^{246,248}Cm in 3n and 4n
channels, and the system ^{51}V+^{244}Pu in 3n channel.Comment: 10 pages, 4 figures, 1 tabl
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