Showing papers by "Mildred S. Dresselhaus published in 1977"
97 citations
TL;DR: In this article, the lattice modes of pure graphite can be divided into intraplanar displacements and interplanar displacement, and the symmetry changes associated with intercalation give rise to both inplane and c-axis zone folding effects.
60 citations
TL;DR: In this paper, electron diffraction through the c-face was used to study the intercalate ordering of graphite-alkali metals (K, Rb, Cs) and graphitehalogens (Br2, IBr, ICl).
33 citations
TL;DR: In this article, a set of phonon dispersion relations for EuSe in the GAMMA-L direction is constructed, which is consistent with a spin-disorder model.
Abstract: Detailed evidence is presented linking the Raman spectra in the magnetic semiconductors EuSe and EuS to their respective magnetic phase diagrams. In particular, spectra for EuSe are presented for the paramagnetic, ferromagnetic, antiferromagnetic (up-arrowup-arrowarrow-downarrow-down), and ferrimagnetic (up-arrowup-arrowarrow-down) spin arrangements and are related to a Brillouin-zone-folding scheme for each magnetic sublattice structure. Based on our spectra a set of phonon dispersion relations for EuSe in the GAMMA-L direction is constructed. We have also obtained for the first time right-angle Raman scattering spectra in EuSe. These results are compared with those obtained in the back-scattering geometry. Of significance is our observation that the broad spectral line extending from ..omega../sub TO/ to ..omega../sub LO/ in the paramagnetic phase persists for laser excitation energies below the fundamental absorption edge, thereby ruling out a hot luminescence mechanism for this feature. Instead, our results are consistent with a spin-disorder model. Resonant Raman enhancement results are given for scattering in ferromagnetically ordered EuS and EuSe, and are related to magnetic-field-modulated magnetoreflectivity spectra. Particular attention has been given to the magnetic-phase dependence of the EuSe modulated spectra in going from the ferrimagnetic to the ferromagnetic spin arrangements.
29 citations
TL;DR: In this paper, an estimate of the hole generation rate in graphite-bromine residue compounds has been made from the interpretation of far-infrared magnetoreflection data, based on the cutoff of the (1, 2) Landau level transition due to the lowering of the Fermi energy upon bromine intercalation.
Abstract: An estimate of the hole generation rate in graphite-bromine residue compounds has been made from the interpretation of far-infrared magnetoreflection data. From the cutoff of the (1,2) Landau level transition due to the lowering of the Fermi energy upon bromine intercalation, we estimate that one hole is generated by 55 \ifmmode\pm\else\textpm\fi{} 10 ${\mathrm{Br}}_{2}$ intercalate molecules. This result is shown to be consistent with estimates based on transport measurements. Furthermore, the observed magnetoreflection resonances confirm that for these compounds ($\ensuremath{\lesssim}1$ mole% ${\mathrm{Br}}_{2}$) the electronic structure in the band overlap region is well described by the Slonczewski-Weiss-McClure band model for approximately the same values of the band parameters as for pure graphite.
25 citations
TL;DR: In this paper, the authors summarize the experimental evidence related to halogen ionization in graphite-halogen compounds and show this evidence to be consistent with a low intercalate ionization and the preservation of the molecular identity of the halogen intercalates.
10 citations
TL;DR: In this paper, a model for the magnetic energy level structure of graphite intercalation compounds in the dilute limit corresponding to stage ≳5.1 eV of the graphite Fermi level was proposed.
Abstract: High field magnetoreflection measurements are reported on the first observation of interband Landau level transitions in residue and lamellar compounds of graphite intercalated with the halogens Br 2 , IBr and ICl. These magnetoreflection spectra are interpreted to yield a model for the magnetic energy level structure of these intercalation compounds in the dilute limit corresponding to stage ≳5. In this dilute limit, the insensitivity of the magnetoreflection resonances to intercalate concentration shows that near the Fermi level for pure graphite the electronic structure of the intercalation compounds is essentially independent of intercalate concentration. This conclusion results from analysis of both infrared and far-infrared magnetoreflection spectra for Landau level transitions within ±0.1 eV of the graphite Fermi level. The model for the electronic structure deduced from the magnetoreflection spectra is supported by Raman scattering results presented for the in-plane lattice modes of carbon atoms in the graphitic layer planes.
7 citations
TL;DR: Anomalies in the lineshapes for resonant Landau level transitions observed in the magnetoreflection spectra of Bi1−xSbx alloys for three important regimes of Sb concentration were reported in this article.
Abstract: Anomalies are reported in the lineshapes for resonant Landau level transitions observed in the magnetoreflection spectra of Bi1−xSbx alloys for three important regimes of Sb concentration: (I) the semimetallic regime x ⪅ 0.04 with the Bi band ordering; (II) the semimetallic regime 0.04 ⪅ x ⪅ 0.08 but with inverted band ordering; and (III) the semiconducting regime 0.08 ⪅ x ⪅ 0.20. Particular attention is given to the different characteristic behaviors of these anomalies in each of the three regimes. These anomalies provide evidence for a magnetic field-induced admixture of the wave-functions for the lowest quantum number valence and conduction band Landau levels. The interpretation of these anomalies supports the band inversion model, including the reversal in the sign of the spin-splitting coefficient G when band inversion occurs.
1 citations