59 research outputs found
Local Charge Excesses in Metallic Alloys: a Local Field Coherent Potential Approximation Theory
Electronic structure calculations performed on very large supercells have
shown that the local charge excesses in metallic alloys are related through
simple linear relations to the local electrostatic field resulting from
distribution of charges in the whole crystal.
By including local external fields in the single site Coherent Potential
Approximation theory, we develop a novel theoretical scheme in which the local
charge excesses for random alloys can be obtained as the responses to local
external fields. Our model maintains all the computational advantages of a
single site theory but allows for full charge relaxation at the impurity sites.
Through applications to CuPd and CuZn alloys, we find that, as a general rule,
non linear charge rearrangements occur at the impurity site as a consequence of
the complex phenomena related with the electronic screening of the external
potential. This nothwithstanding, we observe that linear relations hold between
charge excesses and external potentials, in quantitative agreement with the
mentioned supercell calculations, and well beyond the limits of linearity for
any other site property.Comment: 11 pages, 1 table, 7 figure
Screened Coulomb interactions in metallic alloys: I. Universal screening in the atomic sphere approximation
We have used the locally self-consistent Green's function (LSGF) method in
supercell calculations to establish the distribution of the net charges
assigned to the atomic spheres of the alloy components in metallic alloys with
different compositions and degrees of order. This allows us to determine the
Madelung potential energy of a random alloy in the single-site mean field
approximation which makes the conventional single-site density-functional-
theory coherent potential approximation (SS-DFT-CPA) method practically
identical to the supercell LSGF method with a single-site local interaction
zone that yields an exact solution of the DFT problem. We demonstrate that the
basic mechanism which governs the charge distribution is the screening of the
net charges of the alloy components that makes the direct Coulomb interactions
short-ranged. In the atomic sphere approximation, this screening appears to be
almost independent of the alloy composition, lattice spacing, and crystal
structure. A formalism which allows a consistent treatment of the screened
Coulomb interactions within the single-site mean-filed approximation is
outlined. We also derive the contribution of the screened Coulomb interactions
to the S2 formalism and the generalized perturbation method.Comment: 28 pages, 8 figure
Numerical study of vortex system quantum melting
We report a numerical study of the vortex system in the two dimensional
II-type superconductors. We have proposed a phenomenological model that takes
into account quantum fluctuations of Abrikosov's vortices. The results of the
quantum Monte-Carlo simulations by the SSE algorithm show that the thermal
fluctuations are dominated by quantum fluctuations at low temperatures. In
particular, we demonstrate the possibility of the quantum melting transition
for vortex system in the temperature region where thermal melting transition is
improbable
Screened Coulomb interactions in metallic alloys: II Screening beyond the single-site and atomic sphere approximations
A quantitative description of the configurational part of the total energy of
metallic alloys with substantial atomic size difference cannot be achieved in
the atomic sphere approximation: It needs to be corrected at least for the
multipole moment interactions in the Madelung part of the one-electron
potential and energy. In the case of a random alloy such interactions can be
accounted for only by lifting the atomic sphere and single-site approximations,
in order to include the polarization due to local environment effects.
Nevertheless a simple parameterization of the screened Coulomb interactions for
the ordinary single-site methods, including the generalized perturbation
method, is still possible. We obtained such a parameterization for bulk and
surface NiPt alloys, which allows one to obtain quantitatively accurate
effective interactions in this system.Comment: 24 pages, 2 figure
On the theory of superconductivity in ferromagnetic superconductors with triplet pairing
We point out that ferromagnetic superconductors with triplet pairing and
strong spin-orbit coupling are even in the simplest case at least two-band
superconductors. The Gor'kov type formalism for such superconductors is
developed and the Ginzburg-Landau equations are derived. The dependence of the
critical temperature on the concentration of ordinary point-like impurities is
found. Its nonuniversality could serve as a qualitative measure of the two-band
character of ferromagnetic superconductors. The problem of the upper critical
field determination is also discussed.Comment: 8 pages, no figure; important changes with respect to the previous
versions due to the correction of a mistake: in this new version, a more
general form is considered for the order parameter (the two-components of the
order parameter were considered before as equal, which is in general not
true) ; submitted to Physical Review
Equation of state and elastic properties of face-centered-cubic FeMg alloy at ultrahigh pressures from first-principles
We have calculated the equation of state and elastic properties of
face-centered cubic Fe and Fe-rich FeMg alloy at ultrahigh pressures from first
principles using the Exact Muffin-Tin Orbitals method. The results show that
adding Mg into Fe influences strongly the equation of state, and cause a large
degree of softening of the elastic constants, even at concentrations as small
as 1-2 at. %. Moreover, the elastic anisotropy increases, and the effect is
higher at higher pressures.Comment: 6 figure
Transverse spin dynamics in a spin-polarized Fermi liquid
The linear equations for transverse spin dynamics in weakly polarised
degenerate Fermi liquid with arbitrary relationship between temperature and
polarization are derived from Landau-Silin phenomenological kinetic equation
with general form of two-particle collision integral. The temperature and
polarization dependence of the spin current relaxation time is established. It
is found in particular that at finite polarization transverse spin wave damping
has a finite value at T=0. The analogy between temperature dependences of spin
waves attenuation and ultrasound absorption in degenerate Fermi liquid at
arbitrary temperature is presented. We also discuss spin-polarized Fermi liquid
in the general context of the Fermi-liquid theory and compare it with "Fermi
liquid" with spontaneous magnetization.Comment: 10 page
Phase stability and electronic structure of iridium metal at the megabar range
[EN] The 5d transition metals have attracted specific interest for high-pressure studies due to their extraordinary stability and intriguing electronic properties. In particular, iridium metal has been proposed to exhibit a recently discovered pressure-induced electronic transition, the so-called core-level crossing transition at the lowest pressure among all the 5d transition metals. Here, we report an experimental structural characterization of iridium by x-ray probes sensitive to both long- and short-range order in matter. Synchrotron-based powder x-ray diffraction results highlight a large stability range (up to 1.4 Mbar) of the low-pressure phase. The compressibility behaviour was characterized by an accurate determination of the pressure-volume equation of state, with a bulk modulus of 339(3) GPa and its derivative of 5.3(1). X-ray absorption spectroscopy, which probes the local structure and the empty density of electronic states above the Fermi level, was also utilized. The remarkable agreement observed between experimental and calculated spectra validates the reliability of theoretical predictions of the pressure dependence of the electronic structure of iridium in the studied interval of compressions.The authors thank the financial support of the Spanish Ministry of Science, Innovation and Universities, the Spanish Research Agency (AEI), the European Fund for Regional Development (FEDER) under Grant No. MAT2016-75586-C4-1/2-P and the Generalitat Valenciana under Grant Prometeo/2018/123 (EFIMAT). V. M. acknowledges the Juan de la Cierva fellowship (FJCI-2016-27921) and J.A.S. acknowledges the Ramón y Cajal fellowship program (RYC-2015-17482) and Spanish Mineco Project FIS2017-83295-P. We acknowledge the European Synchrotron Radiation Facility for provision of official research beamtimes, the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU No 2009 00971), Knut and Alice Wallenbergs Foundation Project Strong Field Physics and New States of Matter CoTXS (2014 2019). The interpretation of theoretical results was supported by the Ministry of Science and High Education of the Russian Federation in the framework of Increase Competitiveness Program of NUST MISIS (No. K2-2019-001) implemented by a governmental decree dated 16 March 2013, No 211.Monteseguro, V.; Sans-Tresserras, JÁ.; Cuartero, V.; Cova, F.; Abrikosov, I.; Olovsson, W.; Popescu, C.... (2019). Phase stability and electronic structure of iridium metal at the megabar range. Scientific Reports. 9:1-9. https://doi.org/10.1038/s41598-019-45401-xS199Cynn, H., Klepeis, J. E., Yoo, C.-S. & Young, D. A. 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