Resonant modes due to impurity pairs in sodium chloride

Resonant modes due to apirs F^?-impurities in sodium chloride have been computed using Green function method and the infrared-active modes are compared with experimental results.     

Local modes due to U-centers in RbCl containing potassium additive impurity

The frequencies of the localised modes of vibrations of hydride ions in rubidium chloride containing cation impurity have been computed by Green function technique and compared with the experimental measurements. There is found to be a satisfactory agreement between the theoretical and the experimental values.     

Local and gap modes due to a substitutional impurity in alkali halides: One dimensional treatment

Local modes for substitutional impurity H in NaCl, NaBr and KCl have been calculated. Isotope shift for ³⁵Cl and ³⁷Cl substituted in KI has also been calculated. Good agreement with the experimental data has been obtained.     

Infra-red absorption due to localized modes of vibration of impurity complexes in ionic and semiconductor crystals

A brief account is given of the theory of the vibrations of an imperfect crystal containing isolated impurities and pairs of impurities, and the strength of the induced infra-red absorption is discussed. An analysis is then made, by the methods of group theory, of the energy levels and expected optical transitions of an anharmonic localized oscillator vibrating in a static potential well with various point symmetries. These results are compared with the available experimental data for pairs of impurities and more complicated impurity aggregates in ionic crystals with the fluorite and rocksalt structures, and also for similar defects in the covalent crystals silicon, germanium and some III–V compound materials.     

Lattice dynamics of impurity clusters. Application to pairs

A general solution is obtained for the lattice dynamics of a cluster ofn-impurity atoms using the double-time Green’s function formalism. The cluster is characterized byn-mass defect andm-force constant change parameters. It is shown that this general solution for the Green’s function for then-impurity cluster can also be expressed in terms of the Green’s function for the (n−1)-impurity cluster. As an application, the cluster impurity modes for a pair are calculated using the Debye model for the host lattice dynamics. The splitting of the high frequency local modes and nearly zero frequency resonant modes due to pairs show an oscillatory behaviour on varying the distance of separation between the two impurity atoms. These oscillations are most prominent for two similar impurities and get damped for two dissimilar impurities or if one of the impurities produces a force constant change. The predictions of the calculation provide qualitative explanation of the data obtained from the infrared measurements of the resonant modes in mixed crystal system of KBr_1−c Cl _c : Li⁺ and KBr_1−c I _c : Li⁺.     

Interaction of repulsive impurity pairs in silver

Probe-impurity interactions of In–Cd and In–Zn pairs in silver matrix have been studied using ¹¹¹In-TDPAC measurements. The interactions are repulsive for both the pairs. For 3% alloys, the interaction energy of In–Cd pairs in Ag is 51± 2 meV and that of In–Zn pairs is 19± 1 meV. The Electric Field Gradient (EFG) at ¹¹¹Cd due to a single Cd nn impurity to the In probe is found to be 0.83± 0.04× 10²¹ V/m² while for a Zn impurity is 1.50± 0.05× 10²¹ V/m². Cd–Cd contact interaction in silver is also found to be repulsive. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ferromagnetism in Mn-doped ZnO due to impurity bands

We have prepared quasi-homoepitaxial Zn_0.95Mn_0.05O-films on ZnO substrates by pulsed laser deposition. The thin films were characterized by in situ RHEED during growth, X-ray diffraction and reflectometry, as well as transmission electron microscopy (TEM). The magnetic properties have been analyzed by SQUID magnetometry and by measuring the anomalous Hall effect. By varying the growth conditions (substrate temperature: 200–600 ^∘C, deposition atmospheres: Ar, O₂) a different concentration of impurities has been generated. Our results show that the films are electron doped and exhibit a ferromagnetic coupling that depends on the impurity concentration.     

Strain field due to self-interstitial impurity in Ni

The embedded-atom method have been applied to study the strain field produced by the self-interstitial impurity at the octahedral site in Ni. The calculation have been carried out consistently on the basis of discrete lattice theory, using Kanzaki method. The atomic force constants are evaluated using Wills and Harrison interatomic potential. The dynamical matrix and external force are evaluated considering the interaction up to first nearest neighbors. The atomic displacements are tabulated up to 20NN’s. These displacements are of oscillatory nature and of decreasing magnitude with NN’s distance. The physical properties such as self-interstitial formation energy and volume change calculated using atomic displacements are in accordance with the earlier studies.     

Nuclear relaxation due to a paramagnetic impurity

It is shown that the contributions of two-stage resonance processes in which the state of an electron does not vary as a result of nuclear relaxation are not taken into account in the usual equations for the rate of nuclear relaxation by paramagnetic impurities. In particular, these transitions yield a contribution precisely equal to the contribution of cross-over processes. Nuclear relaxation due to a magnetic ion with singlet ground level in which these processes are particularly great is investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 83–87, June, 1976.The author wishes to express his appreciation to B. Io Kochelaev for discussion of the present results.     

Intrinsic localized modes and nonlinear impurity modes in curved Fermi-Pasta-Ulam chain

We explore the nature of intrinsic localized modes (ILMs) in a curved Fermi-Pasta-Ulam (FPU) chain and the effects of geometry and second-neighbor interaction on the localization and movability properties of such modes. We determine analytically the structure of the localized modes induced by an isotopic light-mass impurity in this chain. We further demonstrate that a nonlinear impurity mode may be treated as a bound state of an ILM with the impurity.      

Temperature dependence of impurity resistivity due to hydrogen in metals

Using a self-consistent calculation, we show that the impurity resistivity of metals containing hydrogen or deuterium decreases as temperature increases. We also predict a significant isotope effect that is largest at O K and vanishes at high temperatures. These effects should be common to all metal-hydrogen systems and could be detected by precision experiments.     

Positive magnetoresistance due to impurity interactions in dilute AuCr alloys

The magnetoresistance of dilute AuCr alloys (2.3–322 at.ppm) has been measured in a wide region of temperature (5-3K) and of magnetic field (up to 60 kG).The “modified Kohler's rule” was used to extract the spin dependent magnetoresistance (?_M) from measured total magnetoresistance.The results has shown that, except for the most dilute specimen, ?_M includes explicitly a positive component in addition to the ordinary negative magnetoresistance proportional to log (H/T). We have attributed this positive ?_M to the effect of the interactions between the Cr impurities by taking consideration of the generalized phase shift expression of magnetoresistance proposed by Soultie.     

Meron pairs and fermion zero modes

Merons, conjectured as a semiclassical mechanism for color confinement in QCD, have been described analytically by either infinite action configurations or an Ansatz with discontinuous action. We construct a smooth, finite action, stationary lattice solution corresponding to a meron pair. We also derive an analytical solution for the zero mode of the meron pair Ansatz, show that it has the qualitative behavior of the exact zero mode of the lattice solution, and propose the use of zero modes to identify meron gauge field configurations in stochastic evaluations of the lattice QCD path integral.     

Localized modes on an Ablowitz-Ladik nonlinear impurity

We study localized modes on a single Ablowitz-Ladik impurity embedded in the bulk or at the surface of a one-dimensional linear lattice. Exact expressions are obtained for the bound state profile and energy. Dynamical excitation of the localized mode reveals exponentially-high amplitude oscillations of the spatial profile at the impurity location. The presence of a surface increases the minimum nonlinearity to effect a dynamical selftrapping.