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.

Disorder dependence of the magnetic moment of the half-metallic ferromagnet NiMnSb from first principles

Abstract: Using half-metallic ferromagnets in spin-dependent devices, like spin valves and ferromagnetic tunnel junctions, is expected to increase the device performance. However, using the half-metallic ferromagnet NiMnSb in such devices led to much less than ideal results. One of the possible sources for this behavior is atomic disorder. First-principles calculations of the influence of atomic disorder on the electronic structure of NiMnSb underline the sensitivity of half-metallic properties in NiMnSb to atomic disorder. In this article, we report on the disorder dependence of the total magnetic moment calculated by applying the layer Korringa–Kohn–Rostoker method in conjunction with the coherent potential approximation. We consider the following types of disorder: (1) intermixing of Ni and Mn, (2) partial occupancy of a normally vacant lattice site by Ni and Mn, and (3) partial occupancy of this site by Mn and Sb. In all cases the composition is kept stoichiometric. All three types of disorder decrease the mome...

Exciton line shapes and migration with stochastic exciton lattice coupling

Abstract: In a recent article, Sumi [J. Chem. Phys. 67, 2943 (1977)] has discussed the optical line shape of an exciton interacting with phonons using a Gaussian Markov process for this interaction. By assuming that the correlation time of the process is nonzero, he was able to explore various limits of (motional) narrowing of the line. His analysis used a dynamic coherent potential approximation (CPA) in order to calculate the line shape. In the present paper, we derive these results in closed analytic form, without the CPA, by using standard analysis. Since our results agree with Sumi very closely, the present approach provides a simple way of understanding the underlying physics. In addition, we show how the exciton density of states enters in a simple way, and compare the hemicircular and the Lorentzian forms for this density of states.

Coherent-Potential Approximation for Disordered Ferromagnetic Binary Alloys

Abstract: The magnetic properties of spin-\textonehalf{} Heisenberg ferromagnetic alloys are calculated. We calculate the spin-wave Green's function in the random-phase approximation and treat the disordered composition-dependent exchange interaction in a coherent-potential approximation (CPA). In the weak-scattering limit, the CPA reproduces the result of the mean-field theory as expected, and in the strong-scattering limit, the CPA predicts such properties as critical concentration, which is beyond the scope of the mean-field theory.

The infrared conductivity of graphene on top of silicon oxide

Abstract: We study the infrared conductivity of graphene at finite chemical potential and temperature taking into account the effect of phonons and disorder due to charged impurities and unitary scatterers, that is, considering all possible single-particle scattering mechanisms. The screening of the long-range Coulomb potential is treated using the random phase approximation coupled to the coherent potential approximation. The effect of the electron-phonon coupling is studied in second-order perturbation theory. The theory has essentially one free parameter, namely, the number of charge impurities per carbon, nCi. Our most important results are the finding of an anomalous enhancement of the conductivity in a frequency region that is blocked by Pauli exclusion, in a picture based on independent electrons, and an impurity broadening of the conductivity threshold, close to twice the chemical potential. We also find that phonons induce Stokes and anti-Stokes lines that produce an excess conductivity, when compared to the far infrared value of σ0=(π/2)e2/h.