408 research outputs found
Multiplet resonance lifetimes in resonant inelastic X-ray scattering involving shallow core levels
Resonant inelastic X-ray scattering (RIXS) spectra of model copper- and
nickel-based transition metal oxides are measured over a wide range of energies
near the M-edge (h=60-80eV) to better understand the properties of
resonant scattering involving shallow core levels. Standard multiplet RIXS
calculations are found to deviate significantly from the observed spectra.
However, by incorporating the self consistently calculated decay lifetime for
each intermediate resonance state within a given resonance edge, we obtain
dramatically improved agreement between data and theory. Our results suggest
that these textured lifetime corrections can enable a quantitative
correspondence between first principles predictions and RIXS data on model
multiplet systems. This accurate model is also used to analyze resonant elastic
scattering, which displays the elastic Fano effect and provides a rough upper
bound for the core hole shake-up response time.Comment: 6 pages, 3 figure
Disorder enabled band structure engineering of a topological insulator surface
Three dimensional topological insulators are bulk insulators with
topological electronic order that gives rise to conducting
light-like surface states. These surface electrons are exceptionally resistant
to localization by non-magnetic disorder, and have been adopted as the basis
for a wide range of proposals to achieve new quasiparticle species and device
functionality. Recent studies have yielded a surprise by showing that in spite
of resisting localization, topological insulator surface electrons can be
reshaped by defects into distinctive resonance states. Here we use numerical
simulations and scanning tunneling microscopy data to show that these resonance
states have significance well beyond the localized regime usually associated
with impurity bands. At native densities in the model BiX (X=Bi, Te)
compounds, defect resonance states are predicted to generate a new quantum
basis for an emergent electron gas that supports diffusive electrical
transport
Modification of Transition-Metal Redox by Interstitial Water in Hexacyanometalate Electrodes for Sodium-Ion Batteries.
A sodium-ion battery (SIB) solution is attractive for grid-scale electrical energy storage. Low-cost hexacyanometalate is a promising electrode material for SIBs because of its easy synthesis and open framework. Most hexacyanometalate-based SIBs work with aqueous electrolyte, and interstitial water in the material has been found to strongly affect the electrochemical profile, but the mechanism remains elusive. Here we provide a comparative study of the transition-metal redox in hexacyanometalate electrodes with and without interstitial water based on soft X-ray absorption spectroscopy and theoretical calculations. We found distinct transition-metal redox sequences in hydrated and anhydrated NaxMnFe(CN)6·zH2O. The Fe and Mn redox in hydrated electrodes are separated and are at different potentials, leading to two voltage plateaus. On the contrary, mixed Fe and Mn redox in the same potential range is found in the anhydrated system. This work reveals for the first time how transition-metal redox in batteries is strongly affected by interstitial molecules that are seemingly spectators. The results suggest a fundamental mechanism based on three competing factors that determine the transition-metal redox potentials. Because most hexacyanometalate electrodes contain water, this work directly reveals the mechanism of how interstitial molecules could define the electrochemical profile, especially for electrodes based on transition-metal redox with well-defined spin states
Extending Minsky's Classifications of Fragility to Government and the Open Economy
Minsky's classification of fragility according to hedge, speculative, and Ponzi positions is well-known. He wrote about fragile positions of individual firms and of the economy as a whole, with the economy transitioning naturally from a robust financial structure (dominated by hedge units) to a fragile structure (dominated by speculative units). In most of Minsky's writing, he introduced government through its impact on the private sector with its spending and balance sheet operations as stabilizing forces (although he insisted that stability is ultimately destabilizing). On a few occasions he also analyzed the government's own balance sheet position. More rarely, Minsky extended his analysis to the open economy, examining the fragility of external debt positions. In these works, he analyzed the United States as the world's bank and discussed the impact of various U.S. balance sheet positions on the rest of the world. This paper will carefully examine Minsky's position on these topics, and will offer an extension of Minsky's work. It will also examine the sustainability of the current twin U.S. deficits
Irreversible proliferation of magnetic moments at cleaved surfaces of the topological Kondo insulator SmB6
The compound SmB is the best established realization of a topological
Kondo insulator, in which a topological insulator state is obtained through
Kondo coherence. Recent studies have found evidence that the surface of SmB
hosts ferromagnetic domains, creating an intrinsic platform for unidirectional
ballistic transport at the domain boundaries. Here, surface-sensitive X-ray
absorption (XAS) and bulk-sensitive resonant inelastic X-ray scattering (RIXS)
spectra are measured at the Sm N-edge, and used to evaluate electronic
symmetries, excitations and temperature dependence near the surface of cleaved
samples. The XAS data show that the density of large-moment atomic multiplet
states on a cleaved surface grows irreversibly over time, to a degree that
likely exceeds a related change that has recently been observed in the surface
4f orbital occupation
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