MgB_2 under pressure: phonon calculations, Raman spectroscopy, and optical reflectance

Abstract

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-center $E_{2g}$ 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 broad spectral features we observed in the Raman spectra at frequencies between 500 and 900 cm${}^{-1}$ cannot be attributed to first-order scattering by zone-center 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${}^{-1}$.

18 pages, 8 figures (EPS), revtex

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Cited by in corpus (14)

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• Review of Transition-Metal Diboride Thin Films
• Prediction of new crystal structure phases in metal borides: a lithium monoboride analog to MgB2
• Crystal structure and lattice dynamics of AlB2 under pressure and implications for MgB2
• Thermodynamics of Two - Band Superconductors: The Case of MgB${}_2$
• Electron-phonon coupling and phonon self-energy in MgB${}_2$: do we really understand MgB${}_2$ Raman spectra ?
• Anharmonic effects in MgB2? A comparative inelastic X-ray scattering and Raman study
• Tuning topological disorder in MgB${}_2$
• Thermodynamic stabilities of ternary metal borides: An ab initio guide for synthesizing layered superconductors
• Electron-phonon coupling and two-band superconductivity of Al- and C-doped MgB2
• Non-adiabatic effects in the phonon dispersion of Mg 1--x Al x B 2
• Possible superlattice formation in high-temperature treated carbonaceous MgB2 at elevated pressure
• A model Hamiltonian for MgB2 which takes into account its unusual phononic features