51,873 research outputs found
Rational material design of mixed-valent high T superconductors
We design, from first principles calculations, a novel family of thallium
halide-based compounds as candidates for new high temperature superconductors,
whose superconductivity is mediated by the recently proposed mechanism of
non-local correlation-enhanced strong electron-phonon coupling. Two prototype
compounds namely CsTlF and CsTlCl are studied with various hole doping
levels and volumes. The critical superconducting temperature T are
predicted to be about 30 K and 20 K with 0.35/f.u. hole doping and
require only modest pressures (10 and 2 GPa), respectively. Our
procedure of designing this class of superconductors is quite general and can
be used to search for other "other high temperature superconductors".Comment: 6- ages, EPL 101, 27002 (2013
Correlation-enhanced electron-phonon coupling: Applications of GW and screened hybrid functional to bismuthates, chloronitrides, and other high Tc superconductors
We show that the electron-phonon coupling (EPC) in many materials can be
significantly underestimated by the standard density functional theory (DFT) in
the local density approximation (LDA) due to large non-local correlation
effects. We present a simple yet efficient methodology to evaluate the
realistic EPC going beyond LDA by using more advanced and accurate GW and
screened hybrid functional DFT approaches. The corrections we propose explain
the extraordinarily high superconducting temperatures that are observed in two
distinct classes of compounds-the bismuthates and the transition metal
chloronitrides, thus solving a thirty-year-old puzzle. Our work calls for the
critically reevaluation of the EPC of certain phonon modes in many other
materials such as cuprates and iron-based superconductors. The proposed
methodology can be used to design new correlation-enhanced high temperature
superconductors and other functional materials involving electron-phonon
interaction.Comment: Substantilly extended version of the previous manuscript, 19 pages,
10 figures, accepted for publication in Phys. Rev.
Almost Sure Stabilization for Adaptive Controls of Regime-switching LQ Systems with A Hidden Markov Chain
This work is devoted to the almost sure stabilization of adaptive control
systems that involve an unknown Markov chain. The control system displays
continuous dynamics represented by differential equations and discrete events
given by a hidden Markov chain. Different from previous work on stabilization
of adaptive controlled systems with a hidden Markov chain, where average
criteria were considered, this work focuses on the almost sure stabilization or
sample path stabilization of the underlying processes. Under simple conditions,
it is shown that as long as the feedback controls have linear growth in the
continuous component, the resulting process is regular. Moreover, by
appropriate choice of the Lyapunov functions, it is shown that the adaptive
system is stabilizable almost surely. As a by-product, it is also established
that the controlled process is positive recurrent
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