Resonant scattering by impurities in metals and the Anderson model

The Anderson Hamiltonian, written in a representation where the extra orbital is not orthogonal to the conduction states, is used to derive a general theory of the electronic structure of dilute alloys. The theory describes both simple impurities in the over-complete or Wolff limit, and transition or rare-earth impurities where the scattering of the conduction electrons has a resonance. The extra-orbital of Anderson is shown to be identical to a bound state extracted from higher bands by the impurity potential, and overlapping the conduction band in energy. The resonant scattering of conduction electrons is described by a pseudopotential, which is singular in energy, in analogy to the theory of band structures of pure transition elements. The position and width of the resonance, as well as a direct scattering potential introduced by the non-orthogonality, are given in terms of Anderson's parameters. The resonance is narrowed by the non-orthogonality and disappears in the over-complete limit.     

The beauty of non-resonant X-ray magnetic scattering

The Canadian Light Source's 11^th Annual Users' Meeting (AUM), held June 9 and 10 in Saskatoon, marked several firsts for the regular gathering of the Canadian synchrotron community. It was the first time the meeting was held in conjunction with an international meeting hosted by the CLS, sharing joint workshops with the Fifth International MEDSI workshop and 15^th Pan-American SRI conference. In addition, for the first time all of the papers presented at the AUM described results obtained with data from the CLS.     

Resonant absorption of electromagnetic radiation in a quantum channel due to the scattering of electrons by impurities

We have found an analytical expression for the absorption coefficient of electromagnetic radiation in a quantum channel with a parabolic confinement potential. The calculation has been performed using the second-order perturbation theory taking into account the scattering of a quasi-one-dimensional electron gas by ionized impurities. We have analyzed the dependences of the absorption coefficient on the frequency of the electromagnetic radiation and the magnetic field. The appearance of additional resonant peaks, which are caused by scattering by impurities, has been found.     

Discrete optical soliton scattering by local inhomogeneities

The nonlinear wave scattering by local inhomogeneities in discrete optical systems is studied both analytically and numerically. The presented theory describes the reflection and transmission of discrete optical solitons at a point defect. In particular, the derived expressions determine the reflected and transmitted pulses from the incident one. In the range of validity, the analytical results are in excellent agreement with the numerical simulations. It is demonstrated that the point defects in structured optical materials represent effective tool for controlling and manipulation of the nonlinear light pulses.     

Resonant light scattering by optical solitons

We consider the process of light scattering by optical solitons in a planar waveguide with homogeneous and inhomogeneous refractive index cores. We observe resonant reflection (Fano resonances) as well as resonant transmission of light by optical solitons. All resonant effects can be controlled in experiment by changing the soliton intensity.     

Quasielastic scattering of synchrotron radiation from non-resonant atoms

The beat pattern produced by nuclear resonant scattering of synchrotron radiation scattered from two stainless steel foils in constant relative motion has been measured at 3-ID beamline at the Advanced Photon Source. Contrary to theoretical prediction and different from the result in glassy material, the scattering in Bragg directions from single crystal of CoGa diffusional smoothening of the quantum beats was absent within the statistical errors. This revised version was published online in August 2006 with corrections to the Cover Date.     

Skew scattering by rare-earth impurities in silver

We have studied the Hall effect of silver containing rare-earth impurities (Gd, Tb, Dy, Ho, Er, Tm, Nd) between 1.2 and 40° K. It turns out that skew scattering by the rare-earth impurities contributes strongly to the Hall effect. The variation of the skew scattering in the rare-earth series allows us to separate what is due respectively to anisotropic terms of the k-f and of the k-d interactions.     

Resonant electromagnetic soliton in a dense plasma

A study is made of the propagation of an electromagnetic wave along a constant magnetic field B₀ in a high-density plasma under cyclotron resonance conditions when the interaction between the electrons and the wave is strongly nonlinear. It is found that the relativistic reduction in the electron gyrofrequency in the field of the electromagnetic pulse stabilizes the wave. A solution is obtained in the form of an envelope soliton and it is shown that its group velocity is considerably reduced.State University, Rostov-on-Don. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 3–7, January, 1994.     

Resonant scattering of solitons

We study the scattering of solitons in the nonlinear Schr?dinger equation on local inhomogeneities which may give rise to resonant transmission and reflection. In both cases, we derive resonance conditions for the soliton's velocity. The analytical predictions are tested numerically in regimes characterized by various time scales. Special attention is paid to intermode interactions and their effect on coherence, decoherence, and dephasing of plane-wave modes which build up the soliton.     

Resonant light scattering by a gradient quantum well

Resonant scattering of monochromatic light by a quantum well with the frequency of its excitonic resonance varying along a certain direction in the plane of the well is studied experimentally and theoretically. It is shown that the simplest model of a thin inhomogeneous layer that yields an exact solution of the direct and inverse scattering problems allows one to successfully describe the experimental observation of resonant scattering by a GaAs/AlGaAs quantum well with the frequency of the exciton resonance linearly varying in the plane of the well.     

Resonant channel coupling in electron scattering by pyrazine

Detailed investigation of the three low-energy resonances seen in electron scattering by the diazabenzene molecule pyrazine reveals that the first two are nearly pure single-channel shape resonances, but the third is, as long suspected, heavily mixed with core-excited resonances built on low-lying triplet states. Such resonant channel coupling is likely to be widespread in pi-ring molecules, including the nucleobases of DNA and RNA, where it may form a pathway for radiation damage.     

Resonant Raman scattering by plasmons in n-type Ge

We have measured the Raman efficiency for plasmon scattering in n-type Ge as a function of laser excitation frequency in the range of the E₁ and E₁+Δ₁ optical gaps (2.1–2.5 eV). Our results can be explained by a mechanism involving the macroscopic electric field that accompanies the plasma oscillation in a manner similar to that responsible for Fröhlich-interaction-induced forbidden LO-phonon resonances in polar semiconductors plus some contribution of the standard cdf mechanism for scattering by plasmons.     

Resonant Raman scattering by strained and relaxed germanium quantum dots

This paper reports on the results of resonant Raman scattering investigations of the fundamental vibrations in Ge/Si structures with strained and relaxed germanium quantum dots. Self-assembled strained Ge/Si quantum dots are grown by molecular-beam epitaxy on Si(001) substrates. An ultrathin SiO₂ layer is grown prior to the deposition of a germanium layer with the aim of forming relaxed germanium quantum dots. The use of resonant Raman scattering (selective with respect to quantum dot size) made it possible to assign unambiguously the line observed in the vicinity of 300 cm^?1 to optical phonons confined in relaxed germanium quantum dots. The influence of confinement effects and mechanical stresses on the vibrational spectra of the structures with germanium quantum dots is analyzed.     

Resonant Raman scattering in germanium

We have studied the spectral dependence of the first order Raman scattering cross section of Ge at room and liquid nitrogen temperatures in the energy region containing the E₁ and E₁ + Δ₁ optical gaps. This region was covered by a fine mesh of points obtained from the discrete lines of three gas lasers and a cw continuously tunable dye laser. Only one resonant peak was observed, as opposed to the two peaks that characterise the absorption and reflection spectra in this region. The shape of this resonance peak can be explained as due to the changes in the electronic polarizability produced by phonon-induced wave function mixing of the spin-orbit split Λ valence band doublet. The observed temperature shift in the resonant energy is much smaller than the one predicted from the known shifts of the optical gaps with temperature. Furthermore the resonant peak at room temperature appears shifted to higher energies when compared with the theoretical peak calculated from the room temperature optical constants. The resonant Raman peak appears to shift with increasing temperature by the full thermal expansion effect plus only a fraction of the electron-phonon interaction shift seen in the optical constants.