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Coherent potential approximation
About: Coherent potential approximation is a research topic. Over the lifetime, 1930 publications have been published within this topic receiving 36805 citations.
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01 Jan 1990
TL;DR: In this paper, the effect of polyacetylene doping on electrical and optical properties was analyzed using coherent potential approximation, where two types of impurities were taken into account: bond-type and site-type with forward scatterings.
Abstract: Doping of polyacetylene, (CH)x, gives qualitative changes in electrical and optical properties at dopant concentrations above a few percent. It now makes materials as conducting as copper. The mechanism of this change has not been so clear. Disorder effects by the doping are analyzed, using the coherent potential approximation. Two types of impurities are taken into account. One is bond-type. They give rise to backward scatterings of electrons. The other is site-type with forward scatterings. The order parameter, electronic band structure, and density of states are obtained as functions of impurity concentration and strengths of impurity potentials. Due to the one-dimensional nature, the formation of impurity band in the gap is suppressed, if strength of the bond impurity is larger than that of the site impurity. When the site impurity is strong enough, a gapless structure takes place at high impurity concentrations. Phase diagrams are extensively given for various impurity strengths.
1 citations
TL;DR: It is shown that the coherent-potential approximation when used in connection with the Green-function formalism of Korringa, Kohn, and Rostoker (KKR-CPA) yields an effective-medium propagator and self-energy that possess the proper analytic structure in the complex-energy plane.
Abstract: It is shown that the coherent-potential approximation when used in connection with the Green-function formalism of Korringa, Kohn, and Rostoker (KKR-CPA) yields an effective-medium propagator and self-energy that possess the proper analytic structure in the complex-energy plane. The proof emphasizes the unifying features of the CPA within the tight-binding and KKR formalisms, and it is valid for the case of both muffin-tin as well as arbitrarily shaped, space-filling potential cells.
1 citations
TL;DR: In this paper, the electronic properties of such A(x)B(1-x)C semiconductors and the band gap bowing can well be described and understood starting from empirical tight binding models for the pure AC and BC systems.
Abstract: For a wide class of technologically relevant compound III-V and II-VI semiconductor materials AC and BC mixed crystals (alloys) of the type A(x)B(1-x)C can be realized. As the electronic properties like the bulk band gap vary continuously with x, any band gap in between that of the pure AC and BC systems can be obtained by choosing the appropriate concentration x, granted that the respective ratio is miscible and thermodynamically stable. In most cases the band gap does not vary linearly with x, but a pronounced bowing behavior as a function of the concentration is observed. In this paper we show that the electronic properties of such A(x)B(1-x)C semiconductors and, in particular, the band gap bowing can well be described and understood starting from empirical tight binding models for the pure AC and BC systems. The electronic properties of the A(x)B(1-x)C system can be described by choosing the tight-binding parameters of the AC or BC system with probabilities x and 1-x, respectively. We demonstrate this by exact diagonalization of finite but large supercells and by means of calculations within the established coherent potential approximation (CPA). We apply this treatment to the II-VI system Cd(x)Zn(1-x)Se, to the III-V system In(x)Ga(1-x)As and to the III-nitride system Ga(x)Al(1-x)N.
1 citations
TL;DR: In this article, the coherent potential approximation (CPA) was applied to the investigation of the off-diagonal disorder effect on the AC conductivity of the disordered binary alloys, due to intraband absorption.
Abstract: The coherent potential approximation (CPA) is applied to the investigation of the off-diagonal disorder effect on the AC conductivity of the disordered binary alloys, due to intraband absorption. The frequency dependence of the conductivity σ(ω) is numerically calculated for various parameters describing the alloy and various positions of the Fermi level in the band. The anomalous behaviour in the frequency dependence of the conductivity is found. The parameter τ(ω) — optical relaxation time, used by many researchers, in this case is invalid.
1 citations
TL;DR: In this paper, a diffusion-like equation is derived within the coherent potential approximation (CPA) for type II (or inhomogeneous), superconducting binary alloys, and the generalized diffusion coefficient satisfies a simple algebraic equation, the coefficients of which are connected to measurable physical quantities.
Abstract: A diffusionlike equation is derived within the coherent potential approximation (CPA) for type II (or inhomogeneous), superconducting binary alloys. Diagrammatic formulation of the CPA is employed to extend the derivations of Eilenberger and Usadel to nondilute random substitutional alloys A1−sBs having arbitrary concentrations and scattering strength. The generalized diffusion coefficient satisfies a simple algebraic equation, the coefficients of which are connected to measurable physical quantities. The diffusionlike equation is valid for arbitrary values of the order parameter at arbitrary temperatures belowTc. When the order parameter Δ is small, simple expansions in terms of Δ would lead immediately to the generalized Landau-Ginzburg equations. The upper critical magnetic field and magnetization are expressed as functions of concentrations of the binary alloy.
1 citations