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.

Insulator-metal-insulator transition and selective spectral-weight transfer in a disordered strongly correlated system

Abstract: We investigate the metal-insulator transitions at finite temperature for the Hubbard model with diagonal alloy disorder. We solve the dynamical mean-field-theory equations with the noncrossing approximation and we use the coherent potential approximation to handle disorder. The excitation spectrum is given for various correlation strength $U$ and disorder. Two successive metal-insulator transitions are observed at integer-filling values as $U$ is increased. An important selective transfer of spectral weight arises upon doping. The strong influence of the temperature on the low-energy dynamics is studied in detail.

Ballistic transport in semiconductor alloys

Abstract: The electronic structure of semiconductor compounds GaAs, InAs, and InP and alloys Ga0.5In0.5As, Ga0.7Al0.3As, and InP0.5As0.5, obtained in the coherent potential approximation, is used to calculate the group velocity and velocity relaxation time limited by longitudinal optical phonons, alloy disorder, and ionized impurities as a function of electron energy at 300 K. The nonparabolic nature of the band structure is found to severely limit the electron mean free path. With the types of interactions considered to date, the presence of L valleys does not limit the mean free path of electrons moving in the 〈100〉 direction. At 1018‐cm−3 doping, electron‐electron interactions reduce the mean free path by only 15% to 20%. InAs and GaInAs alloys offer advantages over all the other materials for devices with base widths greater than 500 A; however, for thinner devices, ∼100 A, no material is appreciably better than GaAs, the III‐V compound currently under best control. The ballistic device‐related properties of se...

Calculation of Ferromagnetic Properties for Ni-Cu Alloys in Coherent Potential Approximation

Abstract: The density of states and local density of states for ferromagnetic Ni-Cu alloys are calculated in the coherent potential approximation. The Hubbard model is assumed and the Hartree-Fock approximation is used. The calculated densities of states for alloys are found to be strongly smoothened out by a rather large potential difference between Ni and Cu atoms. From the calculated results of the density of states, bulk and local magnetic moments and low temperature specific heat coefficient γ are calculated. Moreover, the high-field spin susceptibility at 0 K is calculated. These results are compared with the experimental ones and a qualitative agreement is obtained.

Residual resistivity of diluted III-V magnetic semiconductors

Abstract: The electronic structure and residual resistivity of diluted (Ga, Mn)As magnetic semiconductors are calculated from first principles using the linear muffin-tin orbital method, the coherent potential approximation, and the Kubo-Greenwood linear response theory. Particular attention is paid to the role of native compensating defects such as As antisites and Mn interstitials as well as to different magnetic configurations of the local Mn moments. The order of magnitude of the calculated resistivities compares reasonably well with available experimental data. The concentration variations of the resistivity reflect two basic mechanisms, namely the strength of the impurity scattering and the number of carriers. In agreement with a recent experiment, the calculated resistivities are strongly correlated with the alloy Curie temperatures evaluated in terms of a classical Heisenberg Hamiltonian.

Using density functional theory to describe slowly varying fluctuations at finite temperatures: local magnetic moments in Gd and the 'not so local' moments of Ni.

Abstract: We briefly describe the density functional theory (DFT)-based 'disordered local moment' (DLM) picture for magnetism at finite temperatures. It shows how relatively slowly fluctuating local moments can emerge from the interacting electrons of many materials. Such entities have rigid magnitudes and fluctuate their orientations from atomic site to atomic site on a timescale long compared to other electronic times. We illustrate this theory with calculations of the magnetocaloric effect in Gd where we find excellent agreement with experiments. Fluctuating moments do not appear to establish naturally over such small regions for some other materials. We show how the DFT-DLM theory can be extended to these materials with the use of the Korringa–Kohn–Rostoker nonlocal coherent potential approximation (KKR-NLCPA) to allow for more extensive, slow magnetic fluctuations. We present the first application of this approach by revisiting the description of the magnetic fluctuations prevalent in the paramagnetic state of nickel. We find that local moments can emerge above Tc and that these form coherently over small clumps of atomic sites (4–8 sites).