Helium atom scattering experiments on Fe films of a few monolayers grown on a Cu(001) substrate d... more Helium atom scattering experiments on Fe films of a few monolayers grown on a Cu(001) substrate demonstrate that (a) in a magnetic film the interatomic magnetic forces can be directly probed from the temperature dependence of the Rayleigh wave frequency across the Curie temperature, and (b) the Rayleigh wave velocity and the topmost interlayer spacing, measured as a function of the film thickness, show a simultaneous 10% reduction at 3 to 4 monolayers-an indication of large magnetostrictive effects.
... Rev. 155, 1004(1967). 9. MARADUD1N AA, In Astrophysics anil the Many Body Problem, p. 107. WA... more ... Rev. 155, 1004(1967). 9. MARADUD1N AA, In Astrophysics anil the Many Body Problem, p. 107. WA Benjamin, New York (1963). 10. ... 157,744(1967). References. 1. AJ Sievers, AA Maradudin and SS Jaswal Phys. Rev. 138 (1965), p. A272. ...
Bloch discusses only the ferromagnetic case, but in spite of some suggestions to the contrary t s... more Bloch discusses only the ferromagnetic case, but in spite of some suggestions to the contrary t see D. Mattis, The Theory of Magnetism (Harper and Row Publisher, Inc. , New York, 1965), p. 244], his analysis leads to simi
Raman spectra of iron phosphorus trichalcogenide crystals (FePX3,X =S,Se) are measured, and a com... more Raman spectra of iron phosphorus trichalcogenide crystals (FePX3,X =S,Se) are measured, and a compilation of the peak frequencies is given. The spectral features due to first-order phonon Raman scattering are analyzed and assigned. At low temperatures in iron phosphorus trisulfide the vibrational Raman-scattering efficiency displays an anomalous enhancement and new structures appear. The temperature dependence of the integrated intensity, bandwidth, and frequency of the Raman peaks is studied and correlated with the antiferromagnetic ordering. It is found that the spin superstructure produces a folding of the phonon dispersion curves into the center of the Brillouin zone and activates new phonon modes in the Raman spectrum.
The vibrational structures observed in the absorption spectrum associated with the crystal-field ... more The vibrational structures observed in the absorption spectrum associated with the crystal-field transitions in Mn, Fe, Co, and Ni dichlorides and dibromides are studied in detail at 5 K. The choice of these crystals is motivated by their appreciable molecular character resulting in a small dispersion of optical branches and hence in the appearance of relatively sharp phonon progressions in the crystal-field spectra. Most of these phonon structures are replicas of Raman-active A, g and Eg frequencies and readily interpreted in terms of many-phonon processes induced by the first-order linear electron-phonon interaction. Furthermore, in Mn and Ni dihalides some intraconfigurational transitions display interesting two-phonon progressions which are attributed to the second-order linear electronphonon interaction. The q = 0 phonon frequencies of even symmetry, deduced from vibronic or Raman spectra, and those of odd symmetry, measured by far-infrared transmission, are interpreted in the framework of. a deformationdipole model. Information on the partial covalency of these compounds and on the magnitude of three-body interactions is derived. the discrimination between the two mechanisms is based on their temperature dependence. We have already reported some sharp phonon progressions in Mn and Ni dihalides. ' " The realization that this is a common feature also in Co and Fe dihalides with a layer structure, despite the complications arising from their orbitally degenerate ground state, has suggested the present, more systematic study of the vibrational structures associated with the crystal-field transitions in the dichlorides and dibromides of Mn, 6869 1980 The American Physical Society ' g".~rp} (6} y, re the firstand second-order linear e-p coupling VIBRATIONAL STRUCTURE OF CRYSTAL-FIELD SPECTRA IN.. .
Recent atom-scattering experimental data have stimulated a new investigation on the surface phono... more Recent atom-scattering experimental data have stimulated a new investigation on the surface phonons of some alkali halides. In the framework of Green's-function method applied to breathing-shell model dynamics we have calculated the dispersion curves and a few E-selected densities of states of surface phonons for the (001) surface of NaF and LiF at room temperature. Particular attention is paid to the change in ion polarizabilities occurring at the surface and its effect on the Rayleigh wave frequencies at the zone boundary.
We present the theory of hyper-Raman scattering of light (HRS) from lattice vibrations in an inho... more We present the theory of hyper-Raman scattering of light (HRS) from lattice vibrations in an inhomogeneous surface region of a semiconductor. Inhomogeneities due to surface band bending associated with carrier depletion or accumulation layers are considered, Large inhomogeneities induce local changes of sign in the dielectric permittivity and consequent large enhancements of HRS intensity, The role of carrier scattering and spatial dispersion is discussed together with possible extensions of HRS spectroscopy to Schottky barriers and Ohmic contacts and the development of a novel scanning HRS spectroscopy, PACS 78,30-Infrared and Raman spectra, PACS 78,66-Optical properties of thin films, surfaces, and layer structures (superlattices, heterofunctions and multilayers), PACS 01.30,Ee-Monographs and collections,
We present a study of the Raman and ir spectra of the sp-bonded carbon clusters C60 and C70, perf... more We present a study of the Raman and ir spectra of the sp-bonded carbon clusters C60 and C70, performed in the framework of a three-parameter bond-charge model based on a transferable interatomic potential. A consistent calculation of the relative amplitudes and of the static polarizability has been performed with only one additional parameter besides those entering the dynamics. The calculated spectra are compared with the existing experimental data for C60 and C7Q~Very good agreement is found for the Raman spectrum of both clusters, whereas the agreement for ir spectra is less satisfactory.
ABSTRACT The crossing surface mode and an anomaly in the optical surface-phonon dispersion recent... more ABSTRACT The crossing surface mode and an anomaly in the optical surface-phonon dispersion recently observed in KBr(001) by means of helium scattering are analyzed and interpreted on the basis of a Green's-function calculation of KBr(001) surface dynamics. The nature and origin of crossing modes in isobaric crystals like RbBr and nonisobaric crystals like KBr are reexamined in light of a general mechanism based on LA-LO hybridization in the {l angle}100{r angle} direction. Their dispersion is then accounted for in terms of zone-boundary bands, specifically TAâ. LA-LO hybridization is also invoked to explain the anomaly observed in the optical surface mode.
We theoretically investigate a hypothetical sp 3 form of diamond carbon with 16 atoms per unit ce... more We theoretically investigate a hypothetical sp 3 form of diamond carbon with 16 atoms per unit cell. It contains fivefold rings as a possible result of fullerene transformation under pressure and could be a stable phase of diamond at high pressure. We have calculated the ground-state structure, the cohesive energy, the bulk modulus, and the electronic density of states by means of tight-binding molecular-dynamics and densityfunctional total-energy calculations. Finally we have compared the phonon spectra at ⌫ and the Raman spectra to existing Raman data for a possible noncubic phase of diamond. ͓S0163-1829͑98͒02109-2͔
The particle flux through a micron-sized orifice into vacuum from a source chamber filled with so... more The particle flux through a micron-sized orifice into vacuum from a source chamber filled with solid 4He exhibits a striking sequence of periodic bursts. The period increases (decreases) with pressure (temperature), vanishing at the melting point for temperatures above the upper lambda point at 1.76 K. The oscillations are attributed to a periodic collapse of the solid induced by the accumulation of excess vacancies injected at the orifice and the period provides information on vacancy diffusivity. Dramatic deviations from this behavior below 1.76 K suggest important modifications in the flow properties of solid 4He induced by the excess vacancies.
Helium atom scattering experiments on Fe films of a few monolayers grown on a Cu(001) substrate d... more Helium atom scattering experiments on Fe films of a few monolayers grown on a Cu(001) substrate demonstrate that (a) in a magnetic film the interatomic magnetic forces can be directly probed from the temperature dependence of the Rayleigh wave frequency across the Curie temperature, and (b) the Rayleigh wave velocity and the topmost interlayer spacing, measured as a function of the film thickness, show a simultaneous 10% reduction at 3 to 4 monolayers-an indication of large magnetostrictive effects.
... Rev. 155, 1004(1967). 9. MARADUD1N AA, In Astrophysics anil the Many Body Problem, p. 107. WA... more ... Rev. 155, 1004(1967). 9. MARADUD1N AA, In Astrophysics anil the Many Body Problem, p. 107. WA Benjamin, New York (1963). 10. ... 157,744(1967). References. 1. AJ Sievers, AA Maradudin and SS Jaswal Phys. Rev. 138 (1965), p. A272. ...
Bloch discusses only the ferromagnetic case, but in spite of some suggestions to the contrary t s... more Bloch discusses only the ferromagnetic case, but in spite of some suggestions to the contrary t see D. Mattis, The Theory of Magnetism (Harper and Row Publisher, Inc. , New York, 1965), p. 244], his analysis leads to simi
Raman spectra of iron phosphorus trichalcogenide crystals (FePX3,X =S,Se) are measured, and a com... more Raman spectra of iron phosphorus trichalcogenide crystals (FePX3,X =S,Se) are measured, and a compilation of the peak frequencies is given. The spectral features due to first-order phonon Raman scattering are analyzed and assigned. At low temperatures in iron phosphorus trisulfide the vibrational Raman-scattering efficiency displays an anomalous enhancement and new structures appear. The temperature dependence of the integrated intensity, bandwidth, and frequency of the Raman peaks is studied and correlated with the antiferromagnetic ordering. It is found that the spin superstructure produces a folding of the phonon dispersion curves into the center of the Brillouin zone and activates new phonon modes in the Raman spectrum.
The vibrational structures observed in the absorption spectrum associated with the crystal-field ... more The vibrational structures observed in the absorption spectrum associated with the crystal-field transitions in Mn, Fe, Co, and Ni dichlorides and dibromides are studied in detail at 5 K. The choice of these crystals is motivated by their appreciable molecular character resulting in a small dispersion of optical branches and hence in the appearance of relatively sharp phonon progressions in the crystal-field spectra. Most of these phonon structures are replicas of Raman-active A, g and Eg frequencies and readily interpreted in terms of many-phonon processes induced by the first-order linear electron-phonon interaction. Furthermore, in Mn and Ni dihalides some intraconfigurational transitions display interesting two-phonon progressions which are attributed to the second-order linear electronphonon interaction. The q = 0 phonon frequencies of even symmetry, deduced from vibronic or Raman spectra, and those of odd symmetry, measured by far-infrared transmission, are interpreted in the framework of. a deformationdipole model. Information on the partial covalency of these compounds and on the magnitude of three-body interactions is derived. the discrimination between the two mechanisms is based on their temperature dependence. We have already reported some sharp phonon progressions in Mn and Ni dihalides. ' " The realization that this is a common feature also in Co and Fe dihalides with a layer structure, despite the complications arising from their orbitally degenerate ground state, has suggested the present, more systematic study of the vibrational structures associated with the crystal-field transitions in the dichlorides and dibromides of Mn, 6869 1980 The American Physical Society ' g".~rp} (6} y, re the firstand second-order linear e-p coupling VIBRATIONAL STRUCTURE OF CRYSTAL-FIELD SPECTRA IN.. .
Recent atom-scattering experimental data have stimulated a new investigation on the surface phono... more Recent atom-scattering experimental data have stimulated a new investigation on the surface phonons of some alkali halides. In the framework of Green's-function method applied to breathing-shell model dynamics we have calculated the dispersion curves and a few E-selected densities of states of surface phonons for the (001) surface of NaF and LiF at room temperature. Particular attention is paid to the change in ion polarizabilities occurring at the surface and its effect on the Rayleigh wave frequencies at the zone boundary.
We present the theory of hyper-Raman scattering of light (HRS) from lattice vibrations in an inho... more We present the theory of hyper-Raman scattering of light (HRS) from lattice vibrations in an inhomogeneous surface region of a semiconductor. Inhomogeneities due to surface band bending associated with carrier depletion or accumulation layers are considered, Large inhomogeneities induce local changes of sign in the dielectric permittivity and consequent large enhancements of HRS intensity, The role of carrier scattering and spatial dispersion is discussed together with possible extensions of HRS spectroscopy to Schottky barriers and Ohmic contacts and the development of a novel scanning HRS spectroscopy, PACS 78,30-Infrared and Raman spectra, PACS 78,66-Optical properties of thin films, surfaces, and layer structures (superlattices, heterofunctions and multilayers), PACS 01.30,Ee-Monographs and collections,
We present a study of the Raman and ir spectra of the sp-bonded carbon clusters C60 and C70, perf... more We present a study of the Raman and ir spectra of the sp-bonded carbon clusters C60 and C70, performed in the framework of a three-parameter bond-charge model based on a transferable interatomic potential. A consistent calculation of the relative amplitudes and of the static polarizability has been performed with only one additional parameter besides those entering the dynamics. The calculated spectra are compared with the existing experimental data for C60 and C7Q~Very good agreement is found for the Raman spectrum of both clusters, whereas the agreement for ir spectra is less satisfactory.
ABSTRACT The crossing surface mode and an anomaly in the optical surface-phonon dispersion recent... more ABSTRACT The crossing surface mode and an anomaly in the optical surface-phonon dispersion recently observed in KBr(001) by means of helium scattering are analyzed and interpreted on the basis of a Green's-function calculation of KBr(001) surface dynamics. The nature and origin of crossing modes in isobaric crystals like RbBr and nonisobaric crystals like KBr are reexamined in light of a general mechanism based on LA-LO hybridization in the {l angle}100{r angle} direction. Their dispersion is then accounted for in terms of zone-boundary bands, specifically TAâ. LA-LO hybridization is also invoked to explain the anomaly observed in the optical surface mode.
We theoretically investigate a hypothetical sp 3 form of diamond carbon with 16 atoms per unit ce... more We theoretically investigate a hypothetical sp 3 form of diamond carbon with 16 atoms per unit cell. It contains fivefold rings as a possible result of fullerene transformation under pressure and could be a stable phase of diamond at high pressure. We have calculated the ground-state structure, the cohesive energy, the bulk modulus, and the electronic density of states by means of tight-binding molecular-dynamics and densityfunctional total-energy calculations. Finally we have compared the phonon spectra at ⌫ and the Raman spectra to existing Raman data for a possible noncubic phase of diamond. ͓S0163-1829͑98͒02109-2͔
The particle flux through a micron-sized orifice into vacuum from a source chamber filled with so... more The particle flux through a micron-sized orifice into vacuum from a source chamber filled with solid 4He exhibits a striking sequence of periodic bursts. The period increases (decreases) with pressure (temperature), vanishing at the melting point for temperatures above the upper lambda point at 1.76 K. The oscillations are attributed to a periodic collapse of the solid induced by the accumulation of excess vacancies injected at the orifice and the period provides information on vacancy diffusivity. Dramatic deviations from this behavior below 1.76 K suggest important modifications in the flow properties of solid 4He induced by the excess vacancies.
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