Calculating a local oscillating quasiparticle’s lifetime at screened defects in solids

We report on a novel approach to calculate quasiparticle lifetimes of localized initial states, which decay into the continuum of underlying quasi-free quasiparticle states in the vicinity of point defects and steps in solids. By using this interpretation of the inelastic damping of wavefunctions, the lifetime becomes a local property. In particular, we consider electrons, which are injected by a scanning tunneling microscope tip into the surface state of a noble metal surface. We investigate numerically the configuration of a single scatterer, a chain of scatterers, and a triangular quantum corral. As compared to an exponential increase of the damping from prior theories, we find an oscillating damping together with a linear background of the resulting measurement signal. The different configurations show increased lifetimes with increasing dimensionality as their scattering phase space is decreased.     

Calculation of the inelastic scanning tunneling image of acetylene on Cu(100)

A Green function linear combination of atomic orbitals technique is used to theoretically calculate the "inelastic" scanning tunneling microscope image of a C2H2 molecule adsorbed on Cu(100) and explain previous experimental results. Our analysis of the inelastic scattering process in terms of the orbitals shows that a destructive interference occurs in the inelastic scattering by the C-H bending modes. This results in a much smaller inelastic fraction due to the bending modes as compared to the stretching ones, and explains why the former cannot be observed experimentally.     

Spin wave dispersion on the nanometer scale

Hot electrons injected into antiferromagnetic Mn layers from the tip of a low temperature scanning tunneling microscope have been used to determine the energies, lifetimes, and momenta of antiferromagnetic spin waves on the nanometer scale. The spin waves show a linear dispersion with a velocity of 160+/-10 meV A and lifetimes that scale linearly with energy in agreement with neutron scattering and theory. It is shown that the method is sensitive enough to detect the influence of surface anisotropies on the spin wave dispersion.     

Inelastic electron lifetimes in simple metals: Influence of spin–orbit coupling

Inelastic single‐particle lifetimes due to electron–electron Coulomb interaction are computed ab‐initio for aluminium, silver, gold and copper using an all‐electron density‐functional calculation and a parameter‐free evaluation of the dielectric function. The novel feature is the inclusion of spin– orbit coupling in the wave functions. We show that, even in light metals, spin–orbit interaction is important for the calculation of inelastic lifetimes because it influences the scattering matrix elements. The importance of spin mixing on the lifetimes in aluminium is examined. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

From high resolution spectroscopy to the modeling of potential energy surfaces

Methods and recipes used to establish potential energy surfaces in condensed molecular phases are discussed. The reliability of calculations is tested by confrontation with spectroscopic measurements in crystals. Optical spectroscopy, in particular, hole burning as a line-narrowing technique, as well as high resolution inelastic neutron scattering (INS), are used to resolve tunneling level structures corresponding to large-amplitude atomic and molecular motions. Rotational tunneling of methyl groups is discussed, and new measurements by INS are presented for crystals that are proposed as suitable candidates for optical studies. Translational tunneling in benzoic acid crystals and the role of promoting modes are reviewed, and new measurements of vibrational spectra by inelastic x-ray scattering are compared with INS and Raman spectra.     

On the model for the diffusion of hydrogen in titanium hydride

The diffusion parameters of hydrogen in the gamma phase of titanium hydride are discussed in the light of nuclear magnetic resonance measurements and inelastic neutron scattering data. A comparison with a previously proposed electrostatic model for diffusion is made. It is shown that the electrostatic model is not satisfactory in explaining hydrogen diffusion in titanium. An alternate potential well system based on inelastic neutron scattering data is shown to be consistent with nuclear magnetic resonance measurements. The model can in principle be used for estimating the tunneling contribution to diffusion. The potential well shape is consistent with the notion that for hydrogen diffusion in titanium, the activation energy is given by the difference between the ground state and the well height, in contrast to the case of hydrogen diffusion in niobium where the activation energy is less than this value.     

Resonant enhancement of inelastic light scattering in the fractional quantum Hall regime at ν=1/3

Strong resonant enhancements of inelastic light scattering from the long wavelength inter-Landau level magnetoplasmon and the intra-Landau level spin wave excitations are seen for the fractional quantum Hall state at ν=1/3. The energies of the sharp peaks (FWHM 0.2 meV) in the profiles of resonant enhancement of inelastic light scattering intensities coincide with the energies of photoluminescence bands assigned to negatively charged exciton recombination. To interpret the observed enhancement profiles, we propose three-step light scattering mechanisms in which the intermediate resonant transitions are to states with charged excitonic excitations.     

Spectroscopy of shear horizontal surface phonons by rotation-flip scattering of ortho-H2 molecules

Ortho-H2 molecules in the j=1 state are predicted, on the basis of a simple extension of the distorted wave approximation, to excite shear-horizontal (SH) polarized surface phonon modes, which are symmetry forbidden in inelastic He atom planar scattering. The symmetry breaking is provided by Deltam-rotational flip transitions which couple efficiently to the shear-horizontal modes. A confirmation is provided by the observation of SH surface phonons in phonon inelastic scattering of H2 from NaCl(001).     

Influence of inelastic subbarrier impurity scattering on the nonresonant tunneling transmission of a quasi-one-dimensional tunneling junction with weak structural disorder

The contribution of inelastic subbarrier impurity scattering of tunneling electrons to the nonresonant transmission of a quasi-one-dimensional tunneling junction with weak (low impurity concentrations) structural disorder at temperature T=0 is determined. It is shown that this contribution leads to an increase in the tunneling transmission and conditions are determined for which this increase may be appreciable.     

Scattering involving LO phonons in tunneling to the 2D electron system of a delta layer

Tunneling to both one and two or three subbands of the 2D electron system of a delta-doped layer is observed in Al/δ-GaAs structures. The energy positions of 2D subbands in one sample are varied due to the diamagnetic shift or persistent tunneling photoconductivity. The change of the sign of a step in tunneling conductivity is observed at the threshold of the emission of an LO phonon when a successive subband is involved in tunneling. An increase in conductivity (positive step) is observed for inelastic intrasubband electron-phonon scattering. A decrease in conductivity (negative step) is observed when the ordinary processes of inelastic tunneling are supplemented by intersubband transitions of electrons that have tunneled in 2D electron systems with the emission of an LO phonon.     

Quantum simulation of the Klein paradox with trapped ions

We report on quantum simulations of relativistic scattering dynamics using trapped ions. The simulated state of a scattering particle is encoded in both the electronic and vibrational state of an ion, representing the discrete and continuous components of relativistic wave functions. Multiple laser fields and an auxiliary ion simulate the dynamics generated by the Dirac equation in the presence of a scattering potential. Measurement and reconstruction of the particle wave packet enables a frame-by-frame visualization of the scattering processes. By precisely engineering a range of external potentials we are able to simulate text book relativistic scattering experiments and study Klein tunneling in an analogue quantum simulator. We describe extensions to solve problems that are beyond current classical computing capabilities.     

Role of spin-flip exchange scattering for hot-electron lifetimes in cobalt

The spin-dependent lifetimes of hot electrons in fcc Co films were studied by spin- and time-resolved two-photon photoemission. Even for excitation energies close to the Fermi level, we find almost identical lifetimes for majority and minority electrons. This result contradicts ab initio theories predicting 5 to 10 times longer lifetimes for the majority electrons in 3d ferromagnets. We provide direct experimental evidence that this discrepancy is caused by the dominance of exchange scattering in inelastic electron decay, in combination with the excitation of secondary electrons. The latter are inherent for all real materials and devices.     

High frequency waves in liquid metals

The inelastic scattering of long wavelength neutrons from coherently scattering metals has been used to examine the collective motions of atoms in the liquid state and to make comparisons with the polycrystalline solids. Well-defined peaks in the velocity spectra of the scattered neutrons have been found in both states for lead, rubidium, tin, bismuth and aluminium. These have been used to present parts of the dispersion curves for vibrational modes of motion in the frequency range 1 to 20 × 10¹² rad/sec and wave number range 1 to 3 Å^?1, and to estimate lifetimes of the modes of the order 0.4 × 10^?12 sec in the solid near the melting point and roughly half these values in the liquid.

In polycrystalline aluminium the major contribution to the observed intensity in the solid is due to transverse modes and the observed similarity of the liquid and solid spectra suggests that transverse motions are observed in the liquid also.     

Possible mesonic effects on inelastic proton scattering to the 10.24 MeV 1+ state in 48Ca

Differential cross sections and analyzing powers were measured for inelastic scattering of 160 MeV protons to the ⁴⁸Ca 10.24 MeV, 1⁺ state. DWIA calculations with shell-model wave functions which fit inelastic electron scattering form factors predict too much cross section at small q and too little at large q for inelastic proton scattering. These results are consistent with the q-dependent modification of magnetic transitions anticipated from mesonic effects such as virtual Δ(1232)-hole excitations.     

Néel-vector tunneling in antiferromagnetic molecular clusters

From inelastic neutron scattering experiments, we demonstrate quantum tunneling of the Néel vector in the antiferromagnetic molecular ferric wheel CsFe8. Analysis of the linewidth of the tunneling transition evidences coherent tunneling.     

Spin-dependent electron dynamics in front of a ferromagnetic surface

Exchange splitting and dynamics of image-potential states in front of a 3 monolayer iron film on Cu(100) have been studied with time-, energy-, and spin-resolved bichromatic two-photon photoemission. For the first image-potential state n=1 we observe an exchange splitting of 56 +/- 10 meV and spin-dependent lifetimes of 16 +/- 2 fs for majority-spin and of 11 +/- 2 fs for minority-spin electrons, respectively. The time-resolved studies of both the population and the linewidth of image-potential states manifest that at the magnetic surface not only inelastic but also quasielastic scattering processes are spin dependent.     

On the detection of nuclear spin waves by inelastic neutron scattering

The possibility of measuring nuclear spin waves (NSW) by inelastic neutron scattering is discussed. The differential cross section and scattered state polarization for the scattering of thermal neutrons from systems described by the Suhl-Nakamura Hamiltonian are developed in the Van Hove correlation function formalism; the relevant correlation functions for the Suhl-Nakamura system are computed. The implications of these calculations for the feasibility of detecting nuclear spin wave modes in neutron scattering experiments are discussed.     

中能区反质子与核的非弹性散射

运用多次散射理论的光学势获得反质子的扭曲波.在扭曲波冲量近似下,讨论了中能区反质子与原子核的非弹性散射.考虑了反质子能量从180MeV到1800MeV这一能区¹²C,的2+,3-态微分截面.在这一能区的低能端,(E=180MeV)DWIA能够很好的符合实验,同时,预示了更高能量可能出现的微分截面的理论结果.     

Antiproton-Nucleus Inelastic Scattering at Intermediate Energies

The distorted wave of antiproton is obtained by an optical potential derived from the multiple scattering theory In the framework of the distorted wave impulseapproximation, we discuss the antiproton-nucleus inelastic scattering at intermediate energies. The inelastic differential cross sections of 2+, 3- states at antiproton energies from 180 MeV to 1800 MeV are calculated. It is shown that DWIA fitted the experimented data quite well, and theoretical results of inelastic cross sections at higher energies are predicted.     

Dependence of the intrinsic line width of surface states on the wave vector: The Cu(111) and Ag(111) surfaces

The dependence of the intrinsic line width Γ of electron and hole states due to inelastic scattering on the wave vector k _∥ in the occupied surface state and the first image potential state on the Cu(111) and Ag(111) surfaces has been calculated using the GW approximation, which simulates the self-energy of the quasiparticles by the product of the Greens’s function and the dynamically screened Coulomb potential. Different contributions to the relaxation of electron and hole excitations have been analyzed. It has been demonstrated that, for both surfaces, the main channel of relaxation of holes in the occupied surface states is intraband scattering and that, for electrons in the image potential states, the interband transitions play a decisive role. A sharp decrease in the intrinsic line width of the hole state with an increase in k _∥ is caused by a decrease in the number of final states, whereas an increase in Γ of the image potential state is predominantly determined by an increase of its overlap with bulk states.