Electron-hole excitation

One can clearly see, that for small q, a strong peak in S(q, co) dominates, where sr and Si are close to zero, thus indicating the independent collective correlation of the electrons. For increasing q, Sj gets broader and S(q, co) reveals the spectrum of possible electron-hole excitations. 

The ZSA phase diagram and its variants provide a satisfactory description of the overall electronic structure of stoichiometric and ordered transition-metal compounds. Within the above description, the electronic properties of transition-metal oxides are primarily determined by the values of A, and t. There have been several electron spectroscopic (photoemission) investigations in order to estimate the interaction strengths. Valence-band as well as core-level spectra have been analysed for a large number of transition-metal and rare-earth compounds. Calculations of the spectra have been performed at different levels of complexity, but generally within an Anderson impurity Hamiltonian. In the case of metallic systems, the situation is complicated by the presence of a continuum of low-energy electron-hole excitations across the Fermi level. These play an important role in the case of the rare earths and their intermetallics. This effect is particularly important for the valence-band spectra. 

The conductance for a spacing of 2 /xm between gates g and g2 is shown in Fig. 2. The measured bright and dark curves in the plot can be interpreted as spectral peaks tracing out the dispersions of the elementary excitations in the wires. [3] In the case of noninteracting electrons, the curves are expected to map out parabolas defining the continua of electron-hole excitations across... 

N electron/hole excitations is characterized by the set of excitation energies Cfe P2 where the index k labels the quantum number of excitation p. k labels its quantum number. Assuming a simple model for electron tunneling matrix elements [7]... 

We see that the factor (G5E)N (t2 vq vm E)n represents the probability of tunneling of N electrons or holes from the grain to the metal with 5E being the typical energy of one electron (hole) excitation in the metal. Determination of the factor (3 in (95) requires an application of the instanton method which is capable of careful description of quantum tunneling process between... 

Since the energy of the electron in the Coster-Kronig decay is high up in the continuum (cf. Fig. 2) one can argue that the choice of basis set is not very critical and that neglecting the attraction of the extra hole is compensated for by neglecting the repulsion from coupling the electron-hole excitation to P. 

The spur model, proven to be valid in condensed media, proposes that Ps formation would occur through the reaction of a (nearly) thermalized positron with one of the electrons released by ionization of the medium, at the end of the e+ track, in a small region containing a number of reactive labile species (electrons, holes, excited molecules) [1],... 

Swathi, R. S., and Sebastian, K. L. (2007). Resonance energy transfer from a fluorescent dye molecule to plasmon and electron-hole excitations of a metal nanoparticle. J. Chem. Phys. 126 234701-1-234701-5. 

Electron-hole excitations can be produced in photon absorption or electron energy loss experiments one distinguishes d d excitations, and charge transfer excitations. 

One deals with the ab initio description of electronic excited states. These include the attachment or removal of electrons, the account of direct or inverse photo-emission spectra, and the electron-hole excitations of the d -> d or charge transfer type. Advanced methods are presently under development to account for them the GW method, the SIC method, the LDA-I-U method, etc. However, they imply an increased computation cost, which is not routinely accessible for complex systems, such as most oxide surfaces. These methods are also expected to open the field of strongly correlated materials, among which transition metal oxides, which have important technological applications high-Tc superconductivity, giant magneto-resistance, etc. 

F is the bulk collision constant, A is a positive dimensionless factor, Vf is the Fermi velocity and R the particle radius. From a classical point of view, this modification is supported by the fact that, when the radius is smaller than the bulk mean free path of the electrons, there is an additional scattering factor at the particle surface. This phenomenon, known as the mean free path effect, is abundantly discussed in [19]. In a quantum approach, the boundary conditions imposed to the electron wave functions lead to the appearance of individual electron-hole excitations (Fandau damping) [21] resulting in the broadening of the SPR band proportional to the inverse of the particle radius as in Eq. (8) [22]. A chemical interface damping mechanism has also been considered, leading to the l/R dependence of F [23]. 

The properties of the target are described by its dielectric function s(k, a>), where hk and Hm represent the momentum and energy transfer to the system in an elementary inelastic process. This approach has the possibility of describing in a condensed way the screening of the intruder ions as well as the excitations of valence electrons in the solid, including both collective and single-particle (or electron-hole) excitations [13,14]. The stopping power in... 

To this group belong several models of very different kinds such as the image model (RE-IE), the charge transfer (RE-CT) model, the electron-hole excitation model (RE-EH), and the Raman reflectivity model (RE-RF). These models have very little in common except that they all lead to enhancements by virtue of a resonance scattering mechanism. The validity of the last statement is not always realized by people, but it will be shown below to hold true. 

An approach with indirect injection of electron-hole excitations into nanocrystals by the above described noncontact nonradiative Forster-like energy transfer from a proximal quantum well that can in principle be pumped either electrically or optically, can solve the problem of pumping of nanocrystals. The result obtained by the Klimov group indicate that this energy transfer is fast enough to compete with electron-hole recombination in the quantum well, and results in... 

NMR relaxation and Knight shift In an external field nuclear spins exhibit a Larmor precession with a frequency hyperfine coupling to conduction electrons which leads to spin-flip processes as witnessed by the NMR-relaxation rate and the Knight shift of the resonance frequency Scoq- A review of these important effects for HF superconductors is given by Ton et al. (2003). The relaxation rate is determined by the availability of resonant electron-hole excitations. In the normal state this leads to the Kor-ringa law In the superconducting state the presence of A(k) should lead to a faster... 

The measurements have been also extended to (Pri- LajtlsTl alloys (Bucher et al., 1972 Birgeneau, 1973 Buyers et al., 1975) and to dhcp Pr (Johansson et al., 1970 Birgeneau et al., 1971 Lebech and Rainford, 1971 Lebech et al., 1975), both of which have an exchange coupling close to the critical value. The results are similar to those found for FrsTl. The problem of the line width of the excitons can not be solved within the theory outlined here since it has to include the damping via electron-hole excitations. For an outline how this has to be done we refer to section 5.1.5. 

The presence of conduction electrons can lead to an additional quadrupolar coupling of the RE-ion. In addition they will lead to damping of the collective excitations due to possible electron-hole excitations. It will be demonstrated that the damping of sound waves due to that mechanism is particularly large in the vicinity of a Jahn-Teller phase transition. 

Fig. 17.42. Diagrams for the computation of the propagator D(q, to) for shear waves in the presence of interactions between the RE-ions and optical phonons. Compare with fig. 17.39 where the interaction is via electron-hole excitations instead of optical phonons.

Fig. 56. The calculated phonon line shapes in the mode mixing region at three temperatures. The phonon energy is measured in units of the electron-hole excitation energy t], and the temperature is in units of r]/ke (Liu 1989b).

The basic mechanism for energy dissipation involves phonons, nonadiabatic electron-hole excitation processes, plasmons, exoemission, and chemiluminescence, as described below. 

In 1979, Weber and Eagen" examined the decay channels responsible for the quenching of molecular fluorescence near metal surfaces. They showed that for a molecule located between 20 and 160 A from the surface, 80% of its lost energy will lead to surface plasmon excitation in the metal, while at much shorter distances, surface plasmon excitation will go to zero and electron-hole excitation will increase as a result. 

---