Temperature and field dependent scattering in noble metal alloys

The scattering formalism of Blaker and Harris which is appropriate to potential scattering in dilute cubic alloys is modified to include the spin-dependent scattering. An expression for the total T-matrix which describes the ordinary and exchange scattering by magnetic impurities is obtained. The new formalism is compared with other work in the area and is used to discuss the dHvA data for Kondo alloys based on Cu and Au.     

Temperature and field dependent scattering in noble metal alloys

The scattering formalism of Blaker and Harris which is appropriate to potential scattering in dilute cubic alloys is modified to include the spin-dependent scattering. An expression for the total T-matrix which describes the ordinary and exchange scattering by magnetic impurities is obtained. The new formalism is compared with other work in the area and is used to discuss the dHvA data for Kondo alloys based on Cu and Au.Supported by the National Research Council of Canada.     

Nonequilibrium tunneling effects of interacting Hubbard-Anderson impurities

Nonequilibrium interaction effects of two Hubbard-Anderson impurities have been experimentally studied by means of STM/STS methods and theoretically analyzed using a self-consistent approach based on the Keldysh formalism.     

Localized magnetic excitations of coupled impurities in a transverse Ising ferromagnet

A Green's function formalism is used to calculate the spectrum of excitations of two neighboring impurities implanted in a semi-infinite ferromagnetic. The equations of motion for the Green's functions are determined in the framework of the Ising model in a transverse field and results are given for the effect of the exchange coupling, position and orientation of the impurities on the spectra of localized spin wave modes.     

On the theory of impurities in a lattice of magnetic ions: Crystalline field effects

We present a formalism for treating the problem of impurities in a lattice of magnetic rare earth ions. Latter are subject to a crystalline field and special attention is paid to non-Kramers ions in a singlet ground state. Our calculations are restricted to the paramagnetic regime. We derive the conditions for magnetic localized modes to occur and discuss the appearance of local magnetic instabilities. It is shown that the impurity effects are especially large if the system is close to a magnetic phase transition. Furthermore we compute the influence of impurities on the magnetic transition temperature. For the case of vacancies or nonmagnetic impurities the dependence of the Curie temperature on impurity concentration is derived. It is demonstrated that small amounts of impurities can often completely suppress magnetic ordering.     

Linear alternative to the Boltzmann equation without linearization: III. Impurity scattering and electric field

Our previously reported projection formalism leading to a linear alternative to the Boltzmann (-Uehling-Uhlenbeck) kinetic equation is here applied to standard elastic scattering on impurities in solids and external electric field. In the former case in which the Boltzmann equation is linear, we prove that our formalism reproduces this equation. In the dc as well as ac electric field and for any scattering mechanism, it is verified that inclusion of the field reduces (upon neglecting of the field dependence of scattering processes) in the lowest order to inclusion of just the standard field driving term.     

Spatially inhomogeneous thermo field dynamics

Non-equilibrium thermo field dynamics is extended to treat spatially inhomogeneous systems. A canonical formalism of thermally dissipative semi-free fields describing spatially inhomogeneous situations is presented. With this formalism, a scheme of perturbative calculations is developed and the “on-shell” renormalization condition is discussed. We illustrate this scheme using a model of particles interacting with impurities and find that the self-consistent renormalization condition gives the kinetic equation for the averaged particle number density as well as the renormalized energy and the dissipative coefficient. It is also shown that this kinetic equation can be reduced to the Boltzmann equation in the gradient expansion approximation.     

Hyperfine fields amd electronic structure of non-magnetic impurities in iron

Hyperfine fields of non-magnetic impurities in iron are calculated using the local-density formalism in an embedded cluster model. The hyperfine fields are seen to result from a delicate balance between negative exchange polarized “bound-paired” states and positive “unpaired-band” contributions. Pressure and temperature dependence and effects due to lattice relaxation are discussed.     

Elastic scattering of surface states on three-dimensional topological insulators

Topological insulators as a new type of quantum matter materials are characterized by a full insulating gap in the bulk and gapless edge/surface states protected by the time-reversal symmetry. We propose that the interference patterns caused by the elastic scattering of defects or impurities are dominated by the surface states at the extremal points on the constant energy contour. Within such a formalism, we summarize our recent theoretical investigations on the elastic scattering of topological surface states by various imperfections, including non-magnetic impurities, magnetic impurities, step edges, and various other defects, in comparison with the recent related experiments in typical topological materials such as BiSb alloys, Bi2Te3, and Bi2Se3 crystals.     

Improvement of the thermoelectric efficiency of pyrene-based molecular junction with doping engineering

In this study, the thermoelectric properties of pyrene molecule doped with boron and nitrogen atom at different sites of molecule are investigated using density functional theory and none-equilibrium Green's function formalism in the linear response regime. Our calculations show that when the impurities are added to the edge of the molecule, the anti-resonant peaks will appear in the transmission diagram in the vicinity of the Fermi energy level. So it increases the thermoelectric figure of merit of the system in comparison with the one that the impurity is located in the center of molecule. Additionally,the seebeck coefficient signs are not the same among the B, N, and N B doped devices, indicating that the types of the carriers can be changed with different types of doping.     

Quantitative approach of Auger electron spectrometry: II. Experimental part

We illustrate the formalism proposed in part one by two studies: thermal segregation of impurities on the surface of a titanium sample, and chemical depth profiling of a passive film formed on stainless steel. The choice of an Auger transition which does not involve valence electrons is particularly emphasized to obtain a satisfactory quantification, when active species are present on the surface.     

Self-consistent calculation of hyperfine fields and adiabatic potential of impurities in iron

Hyperfine fields of impurities of the atomic number Z=1–56 at the substitutional site and those of light impurities of Z=1–9 at the interstitial sites in ferromagnetic iron are calculated by the KKR method adapted to the system containing a single impurity atom. The potential of the impurity atom is determined self-consistently by use of the local spin density functional formalism. The results for nonmagnetic sp valence impurities agree with those of the previous nonself-consistent calculation by Katayama-Yoshida, Terakura and Kanamori except for a few cases, confirming their theory of the systematic variation of hyperfine fields. The calculation for magnetic impurities of transition elements is presented for the first time in this paper. The calculations mentioned so far assume that impurities are situated at the center of each site. For the purpose of discussing the stability of the impurity positions, the change of the adiabatic potential due to displacements from the center is calculated by carrying out similar self-consistent calculations for off-center impurity positions. It is concluded that positive muon and some light impurities including boron will be displaced from the center when trapped in a vacancy.     

First principle calculation of the electronic and magnetic properties of Mn-doped 6H-SiC

The electronic and magnetic properties of 6H-SiC with Mn impurities have been calculated using GGA formalism. Various configurations of Mn sites were considered. It was found that 6H-SiC doped with Mn atoms possess a moment for both types of substitution. The Mn atom at Si site possesses larger magnetic moment than Mn atom at C site. The energy levels appearing in the band gap due to vacancies and due to Mn impurities are determined and the calculated densities of states (DOSs) are used to analyse the different value of the magnetic moments for different types of substitution. A model that explains the magnetic moment at Mn site is proposed.     

Nuclear spin-lattice relaxation of impurities in ferromagnetic iron

Due to the development of Green's function method the calculation of the nuclear spin-lattice relaxation time of impurities in ferromagnets has become feasible in the last years. We present the result of calculations for allsp andd impurities in ferromagnetic iron. The calculations are based on the density functional formalism. They well, reproduce the experimental trend of the relaxation timeT ₁ for bothsp andd impurities. By decomposing the relaxation rate into various contributions, we explain the observed systematic behavior ofT ₁ T in terms of the local electronic structure.     

Density of states in the presence of a strong magnetic field and random impurities

A supersymmetric formalism is used to rederive a recent beautiful result of Wegner concerning the density of state of an electron gas in the presence of a strong magnetic field and impurities. The derivation is simple and applicable to any (local) distribution of scatterers. Explicit formulae are given in two dimensions. A Poisson distribution of scatterers leads to an interesting condensation phenomenon when the magnetic field is increased.     

Scattering theory of defects in crystals

The theory of scattering is applied here to the problem of the electronic states of impurities. The S, T and K matrices, the Lippman-Schwinger and Dyson equations are used to formulate the problem. The standard concepts, methods and results of scattering theory applied to impurities discussed include the scattering amplitude, the Fredholm determinant, dispersion relations, Regge poles, Levinson's theorem and Fadeev's equations. Physical consequences considered are the change in density of states, eigenstates and transport theory. The necessity of extending the scattering formalism to many-body theory is discussed. The relation between scattering theory and other methods of impurity theory is also mentioned.     

D.C. electrical resistivity as a functional of generalized dynamical susceptibilities—Comparison of different methods

The d.c. electrical resistivity is considered for a general solid state model characterized by local interactions of the charge carriers with a system of scatterers which may be e.g. quasiparticles, spins or impurities. A basic relationship - valid over the full temperature range - between the electrical resistivity of the charge carrier system (without magnetic field) and the generalized dynamical susceptibility of the scattering system is derived in the weak scattering limit. The equivalence of the following methods is shown: Boltzmann equation approach (variation procedure), Mori formalism, force-force correlation function method (for the total forces on the charge carriers), and the method of the transformed Liouville equation; herewith the equivalence with the Kubo or Green function method, the Zubarev formalism, the information-theoretical method and the Zwanzig formalism is also given. As a specific example, the s-d exchange model for the scattering of conduction electrons by localized spins is discussed including the corresponding electron-magnon system as a low-temperature approximation.     

Electronic structure of magnetic and non-magnetic substitutional 3d transition metal impurities in germanium

The electronic structure around the ideal 3d transition metal impurities at substitutional site of germanium is calculated self-consistently within the local density formalism. Chemical trend of 3d impuritiy levels caused by the strong p-d hybridization, is revealed in the case of non-magnetic state. The magnetic state of the iron impurity is also presented and the local magnetic moment experienced by iron impurity is calculated to be 3.72μ_B.     

Semi-analytic study on the conductance of a lengthy armchair honeycomb nanoribbon including vacancies,defects,or impurities

We present a semi-analytic method to study the electronic conductance of a lengthy armchair honeycomb nanoribbon in the presence of vacancies, defects, or impurities located at a small part of it. For this purpose, we employ the Green's function technique within the nearest neighbor tight-binding approach. We first convert the Hamiltonian of an ideal semiinfinite nanoribbon to the Hamiltonian of some independent polyacetylene-like chains. Then, we derive an exact formula for the self-energy of the perturbed part due to the existence of ideal parts. The method gives a fully analytical formalism for some cases such as an infinite ideal nanoribbon and the one including linear symmetric defects. We calculate the transmission coefficient for some different configurations of a nanoribbon with special width including a vacancy, edge geometrical defects, and two electrical impurities.