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Evolution of superconductivity in K2-xFe4+ySe5: Spectroscopic studies of X-ray absorption and emission.
This study investigates the evolution of superconductivity in K2-xFe4+ySe5 using temperature-dependent X-ray absorption and resonant inelastic X-ray scattering techniques. Magnetization measurements show that polycrystalline superconducting (SC) K1.9Fe4.2Se5 has a critical temperature (T c) of âŒ31 K with a varying superconducting volume fraction, which strongly depends on its synthesis temperature. An increase in Fe-structural/vacancy disorder in SC samples with more Fe atoms occupying vacant 4d sites is found to be closely related to the decrease in the spin magnetic moment of Fe. Moreover, the nearest-neighbor Fe-Se bond length in SC samples exceeds that in the non-SC (NS) sample, K2Fe4Se5, which indicates a weaker hybridization between the Fe 3d and Se 4p states in SC samples. These results clearly demonstrate the correlations among the local electronic and atomic structures and the magnetic properties of K2-xFe4+ySe5 superconductors, providing deeper insight into the electron pairing mechanisms of superconductivity
Wall Crossing, Quivers and Crystals
We study the spectrum of BPS D-branes on a Calabi-Yau manifold using the 0+1
dimensional quiver gauge theory that describes the dynamics of the branes at
low energies. The results of Kontsevich and Soibelman predict how the
degeneracies change. We argue that Seiberg dualities of the quiver gauge
theories, which change the basis of BPS states, correspond to crossing the
"walls of the second kind." There is a large class of examples, including local
del Pezzo surfaces, where the BPS degeneracies of quivers corresponding to one
D6 brane bound to arbitrary numbers of D4, D2 and D0 branes are counted by
melting crystal configurations. We show that the melting crystals that arise
are a discretization of the Calabi-Yau geometry. The shape of the crystal is
determined by the Calabi-Yau geometry and the background B-field, and its
microscopic structure by the quiver Q. We prove that the BPS degeneracies
computed from Q and Q' are related by the Kontsevich Soibelman formula, using a
geometric realization of the Seiberg duality in the crystal. We also show that,
in the limit of infinite B-field, the combinatorics of crystals arising from
the quivers becomes that of the topological vertex. We thus re-derive the
Gromov-Witten/Donaldson-Thomas correspondence
Operational approach to open dynamics and quantifying initial correlations
A central aim of physics is to describe the dynamics of physical systems.
Schrodinger's equation does this for isolated quantum systems. Describing the
time evolution of a quantum system that interacts with its environment, in its
most general form, has proved to be difficult because the dynamics is dependent
on the state of the environment and the correlations with it. For discrete
processes, such as quantum gates or chemical reactions, quantum process
tomography provides the complete description of the dynamics, provided that the
initial states of the system and the environment are independent of each other.
However, many physical systems are correlated with the environment at the
beginning of the experiment. Here, we give a prescription of quantum process
tomography that yields the complete description of the dynamics of the system
even when the initial correlations are present. Surprisingly, our method also
gives quantitative expressions for the initial correlation.Comment: Completely re-written for clarity of presentation. 15 pages and 2
figure
Tunable Emergent Heterostructures in a Prototypical Correlated Metal
At the interface between two distinct materials desirable properties, such as
superconductivity, can be greatly enhanced, or entirely new functionalities may
emerge. Similar to in artificially engineered heterostructures, clean
functional interfaces alternatively exist in electronically textured bulk
materials. Electronic textures emerge spontaneously due to competing
atomic-scale interactions, the control of which, would enable a top-down
approach for designing tunable intrinsic heterostructures. This is particularly
attractive for correlated electron materials, where spontaneous
heterostructures strongly affect the interplay between charge and spin degrees
of freedom. Here we report high-resolution neutron spectroscopy on the
prototypical strongly-correlated metal CeRhIn5, revealing competition between
magnetic frustration and easy-axis anisotropy -- a well-established mechanism
for generating spontaneous superstructures. Because the observed easy-axis
anisotropy is field-induced and anomalously large, it can be controlled
efficiently with small magnetic fields. The resulting field-controlled magnetic
superstructure is closely tied to the formation of superconducting and
electronic nematic textures in CeRhIn5, suggesting that in-situ tunable
heterostructures can be realized in correlated electron materials
One-dimensional Topological Edge States of Bismuth Bilayers
The hallmark of a time-reversal symmetry protected topologically insulating
state of matter in two-dimensions (2D) is the existence of chiral edge modes
propagating along the perimeter of the system. To date, evidence for such
electronic modes has come from experiments on semiconducting heterostructures
in the topological phase which showed approximately quantized values of the
overall conductance as well as edge-dominated current flow. However, there have
not been any spectroscopic measurements to demonstrate the one-dimensional (1D)
nature of the edge modes. Among the first systems predicted to be a 2D
topological insulator are bilayers of bismuth (Bi) and there have been recent
experimental indications of possible topological boundary states at their
edges. However, the experiments on such bilayers suffered from irregular
structure of their edges or the coupling of the edge states to substrate's bulk
states. Here we report scanning tunneling microscopy (STM) experiments which
show that a subset of the predicted Bi-bilayers' edge states are decoupled from
states of Bi substrate and provide direct spectroscopic evidence of their 1D
nature. Moreover, by visualizing the quantum interference of edge mode
quasi-particles in confined geometries, we demonstrate their remarkable
coherent propagation along the edge with scattering properties that are
consistent with strong suppression of backscattering as predicted for the
propagating topological edge states.Comment: 15 pages, 5 figures, and supplementary materia
Macrophage migration inhibitory factor regulates interleukin-6 production by facilitating nuclear factor-kappa B activation during Vibrio vulnificus infection
No Benefit from Chronic Lithium Dosing in a Sibling-Matched, Gender Balanced, Investigator-Blinded Trial Using a Standard Mouse Model of Familial ALS
Background: In any animal model of human disease a positive control therapy that demonstrates efficacy in both the animal model and the human disease can validate the application of that animal model to the discovery of new therapeutics. Such a therapy has recently been reported by Fornai et al. using chronic lithium carbonate treatment and showing therapeutic efficacy in both the high-copy SOD1G93A mouse model of familial amyotrophic lateral sclerosis (ALS), and in human ALS patients. Methodology/Principal Findings: Seeking to verify this positive control therapy, we tested chronic lithium dosing in a sibling-matched, gender balanced, investigator-blinded trial using the high-copy (average 23 copies) SOD1G93A mouse (n = 27â28/group). Lithium-treated mice received single daily 36.9 mg/kg i.p. injections from 50 days of age through death. This dose delivered 1 mEq/kg (6.94 mg/kg/day lithium ions). Neurological disease severity score and body weight were determined daily during the dosing period. Age at onset of definitive disease and survival duration were recorded. Summary measures from individual body weight changes and neurological score progression, age at disease onset, and age at death were compared using Kaplan-Meier and Cox proportional hazards analysis. Our study did not show lithium efficacy by any measure. Conclusions/Significance: Rigorous survival study design that includes sibling matching, gender balancing, investigato
Advances in small lasers
M.T.H was supported by an Australian Research council Future Fellowship research grant for this work. M.C.G. is grateful to the Scottish Funding Council (via SUPA) for financial support.Small lasers have dimensions or modes sizes close to or smaller than the wavelength of emitted light. In recent years there has been significant progress towards reducing the size and improving the characteristics of these devices. This work has been led primarily by the innovative use of new materials and cavity designs. This Review summarizes some of the latest developments, particularly in metallic and plasmonic lasers, improvements in small dielectric lasers, and the emerging area of small bio-compatible or bio-derived lasers. We examine the different approaches employed to reduce size and how they result in significant differences in the final device, particularly between metal- and dielectric-cavity lasers. We also present potential applications for the various forms of small lasers, and indicate where further developments are required.PostprintPeer reviewe
Rhodium Nanoparticle Shape Dependence in the Reduction of NO by CO
The shape dependence of the catalytic reduction of nitric oxide by carbon monoxide on rhodium nanopolyhedra and nanocubes was studied from 230 to 270 degrees C. The nanocubes are found to exhibit higher turnover frequency and lower activation energy than the nanopolyhedra. These trends are compared to previous studies on Rh single crystals.Chemistry, PhysicalSCI(E)EI21ARTICLE3-4317-32213
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