MgB2under pressure: phonon calculations, Raman spectroscopy, and optical reflectance

作者：Karel Kunc, I. Loa, K. Syassen, Reinhard Karl Kremer, Kwangwon Ahn · 发表于：Journal of Physics Condensed Matter · 年份：2001 · DOI：10.1088/0953-8984/13/44/310 · 被引用次数：77 · 研究领域：Superconductivity in MgB2 and Alloys、Physics of Superconductivity and Magnetism、Thermal Expansion and Ionic Conductivity

The effect of pressure on optical phonon frequencies of MgB 2 has been calculated using the frozen-phonon approach based on a pseudopotential method. Grüneisen parameters of the harmonic mode frequencies are reported for the high-frequency zone-centre E 2g and B 1g and the zone-boundary E 2u and B 2u modes at A. Anharmonic effects of phonon frequencies and the implications of the calculated phonon frequency shifts for the pressure dependence of the superconducting transition temperature of MgB 2 are discussed. Also reported are Raman and optical reflectance spectra of MgB 2 measured at high pressures. The experimental observations in combination with calculated results indicate that the broad spectral features that we observed in the Raman spectra at frequencies between 500 and 900 cm -1 cannot be attributed to first-order scattering by zone-centre modes, but originate in part from a chemical species other than MgB 2 at the sample surface and in part from a maximum in the MgB 2 phonon density of states. Low-temperature Raman spectra taken at ambient pressure showed increased scattering intensity in the region below 300 cm -1 .