E. Burstein

“Giant” Raman scattering by adsorbed molecules on metal surfaces☆

Abstract The very large Raman scattering cross-section of adsorbed molecules, such as pyridine and CN-, on Ag is attributed to mechanisms involving either electron-hole pair excitations in the surface region of the metal or charge-transfer excitations between the metal substrate and the adsorbed molecules.

Giant Raman scattering by pyridine and CN− adsorbed on silver

The giant RS by pyridine and CN− on Ag is accompanied by a strong RS continuum which is attributed to inelastic light scattering by charge carrier-excitations. The enhanced RS by the adsorbed molecules and by the charge carrier-excitations are attributed to surface roughness enhanced EM fields at the metal surface resulting from the excitation of transverse collective electron-excitations and surface-EM modes, and to surface roughness-induced radiative-excitation and radiative-recombination of particle-hole pairs.

Inelastic light scattering by charge carrier excitations in two-dimensional plasmas: Theoretical considerations

Abstract We discuss the single particle and collective charge carrier excitations of the two-dimensional plasmas that occur in non-polar semiconductors and the microscopic mechanisms for the resonant inelastic light scattering by the single particle and collective inter-subband excitations. Two limiting cases are analyzed, the “flat-band” model which is a rough approximation to the configuration used by Pinczuk et al., and the “bent-band” model in which Franz—Keldysh effects play an important role, that is an approximation to the configuration used by Abstreiter and Ploog. Unlike Raman scattering by optical phonons, the dominant contributions to the light scattering by the single particle and collective charge carrier excitations come from scattering processes at optical energy gaps, such as the E0+Δ0 gap, that directly involve the charge carriers, particularly in non-polar semiconductors. In III–V compound semiconductors sizeable contributions to the inelastic scattering by coupled LO phonon-collective inter-subband excitation modes may be expected to come from electro-optic, deformation potential and Frohlich scattering processes at the E1 and E1+Δ1 gaps.

Surface polaritons on semi-infinite gyromagnetic media

A macroscopic theory of surface polaritons on semi-infinite magnetic media is presented. The general nature of surface polaritons on magnetic media is discussed. In the configuration k, M0, and n mutually perpendicular (where k is the propagation wavevector, M0 is the static magnetization of the medium, and n is the outward normal to the surface), the surface polaritons are TE modes with H elliptically polarized in the sagittal plane. The surface polaritons, which exist on a ferromagnetic insulator, exhibit nonreciprocal propagation characteristics of a medium with gyromagnetic permeability. A new branch of the surface polariton dispersion curve is demonstrated. The corresponding magnon type surface polaritons do not occur on a ferromagnetic metal. The possible experimental observation of the magnon type surface polariton modes on a ferromagnetic insulator is also discussed.

Surface polaritons on semi-infinite anisotropic media

Abstract We have investigated the nature of polaritons which propagate on the surface of semi-infinite anisotropic dielectric and magnetic media and find that the surface polaritons are regular surface waves [i.e., the penetration constant α (ω) is real] only for special orientations of the wave vector k and of the normal to the surface n relative to the principal axes. In the case of biaxial crystals, regular surface polaritons occur when k and/or n is along a principal axis of the dielectric tensor e(ω) for dielectric media [or the magnetic permeability tensor μ(ω) for magnetic media]. When k and n are both directed along principal axes, the surface polaritons are TM with E in the saggital plane for dielectric media. One finds that surface polaritons which are coupled photon-virtual surface dipole excitation modes can exist on “surface active” anisotropic media in addition to the familiar coupled photon-real surface dipole excitation modes. When neither k nor n are along principal axes, the surface polaritons that occur are, with the exception of special orientations, “generalized” surface waves [i.e., α(ω) is complex]. The Poynting vectors of the propagating surface polaritons are always in the plane of the surface but not, in general, along k. These results, which hold for uniaxial crystals, are also applicable to gyromagnetic media and to gyrodielectric media. This theory is also applicable to surface polaritons which propagate along the interface between two media, one or both of which is anisotropic, and with one or the other serving as the “surface active” medium.

Virtual excitation type surface polaritons on anisotropic media

Abstract We discuss the nature of a new type of surface polariton which occurs on anisotropic media, involving a photon coupled to a surface virtual excitation. Dispersion curves are calculated for α-quartz, where both real excitation type and virtual excitation type surface polaritons are predicted. The dispersion curves for virtual excitation surface polaritons are found to remain at small wavevector, and the endpoints of the dispersion curves terminate on the bulk polariton dispersion curves in the two media. The virtual excitation surface polaritons which occur on gyromagnetic and gyrodielectric media are also noted.

Role of surface electronic transitions in linear and nonlinear electromagnetic phenomena at noble metal surfaces: beyond jellium☆

Abstract We treat for the first time the contributions to the linear and nonlinear optical response of noble metal surfaces from surface electronic transitions involving intrinsic surface states, Rydberg states and surface modified continuum states, and in particular formulate SHG, and 3WM in general, in terms of three-step processes involving three virtual surface electronic transitions. The surface electronic transitions lead to differences in reflection by (111) and (110) surfaces and to an anisotropic reflection by the (110) surfaces. They also lead to differences in the energy and dispersion of the surface plasmons on Ag(111) and Ag(110) and to anisotropic dispersion of the surface plasmons on Ag(110). 3WM at the (110) and (111) surfaces of Cu and Ag is discussed in terms of specific three-step processes at high symmetry points in the surface Brillouin zones. Processes involving transitions between intrinsic surface states at the -Y point of the (110) surface Brillouin zone are shown to lead to resonances in the dependence of χ2y′y′z′ and χ2y′y′z′ the frequency of the input, or output EM waves.

de Haas‐van Alphen Effect in p‐Type PbTe and n‐Type PbS

A study of the de Haas‐van Alphen oscillations in the magnetic susceptibility has been carried out in p‐type PbTe and n‐type PbS. Measurements have been made on oriented single crystal samples with carrier concentrations of the order of 1018/cm3 in pulsed magnetic fields up to 125 kgauss. The results for p‐type PbTe indicate that the valence bands have a maximum at k=0, and four equivalent maxima at the {111} Brillouin zone faces. The 〈111〉 ellipsoids have a longitudinal mass to transverse mass ratio of 6.4±0.3. From the temperature dependence of the amplitude of the oscillations we obtain a value of 0.043±0.006 m0 for the transverse effective mass. The data indicate that the (000) maximum and the (111) maxima lie within 0.002±0.002 ev of each other. The data also indicate an effective broadening temperature of about 8°K which is attributed to inhomogeneities in the carrier concentrations in the samples investigated. Preliminary results on n‐type PbS show a single isotropic Fermi surface cross section wit...

Interaction of surface magnetoplasmons and surface optical phonons in polar semiconductors

Abstract A theoretical investigation has been carried out of surface polaritons associated with surface magnetoplasmons coupled to surface optical phonons in polar semiconductors. The coupled mode frequencies are calculated for several orientations of the magnetic field relative to the surface and the direction of propagation in the large wave vector (unretarded) limit. Dispersion curves are calculated for the configuration in which the magnetic field is parallel to the surface and is perpendicular to the wave vector. Experimental possibilities for observing the interaction effects are discussed.

Observation of magnetoplasma type surface polaritons on n-InSb

Abstract Surface polariton dispersion curves have been obtained for an n-InSb—air interface in a magnetic field using the ATR method and are found to be in qualitative agreement with theory. In particular the curves show the predicted non-reciprocal nature of the surface polariton propagation, and the appearance of virtual excitation type branches of the dispersion curves. On the basis of data obtained in zero magnetic field on etched surfaces, the quantitative differences between experimental and theoretical dispersion curves are attributed to surface damage.