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Here we report synthesis and characterization of Mg1−xScxB2 (0.12Tc>6 K. We find that the Sc doping moves the chemical potential through the 2D/3D electronic topological transition (ETT) in the σ band where the "shape resonance" of interband pairing occurs. In the 3D regime beyond the ETT we observe a hardening of the E2g Raman mode with a significant line-width narrowing due to suppression of the Kohn anomaly over the range 0

Raman spectra were measured for the full range of hole doping of the orthomanganites of the form La 1Ϫx Ca x MnO 3 (0рxр1) from ambient temperature to 75 K. Two high-frequency phonons that we assign to stretching modes of the oxygen atoms in the MnO 6 octahedra soften below the transition temperature to ferromagnetic insulator and disappear at a temperature that depends on the Ca concentration. The correlation of their properties with the lattice distortions is examined. At room temperature, and for xϳ0.35 and xϳ0.70, phonons attributed to the relative rotations of the octahedra show a strong correlation with the octahedral distortion and the reported low-temperature modifications of the magnetic properties of these compounds.

A latticedynamics approach to the acoustic signal by a uniformly moving dislocation Expressions are derived for the effective phonon deformation potentials of polycrystalline materials, based on the properties of tensor invariants and the Voigt-Reuss-Hill averages [Proc. Phys. Soc. London Sect. A 65,349 (1952)]. These results, and similar ones for the elastic constants, are used to determine the effect of strains on the long-wavelength optical phonons exhibited by such materials. Application to polycrystalline Si shows that under a uniaxial or biaxial stress, the triply degenerate phonons split into singlet and doublet components that shift at different rates and appear indistinguishably in the Raman spectrum. The implications of such effects on the Raman band shape are discussed. 3346