Electron–phonon coupling properties in MgB₂observed by Raman scattering

Abstract

The influence of sintering temperature on the critical transition temperature, Tc, for MgB2 superconductor was investigated systematically with the aid of room temperature Raman scattering measurements and Raman spectral fit analysis. The Raman spectra for all samples can be fitted with one phonon peak coming from the E2g mode at the Γ point of the Brillouin zone and two peaks coming from sampling of the phonon density of states (PDOS) due to disorder. The enhanced E2g mode in the Raman spectra with increasing sintering temperature shows gradual strengthening of the electron–phonon coupling (EPC) in MgB2, which is the reason why the Tc of samples increases with increasing sintering temperature. The strength of electron–E2g coupling is estimated to be about 2.0 ± 0.5, which is larger than the average strength of the coupling of electrons with all the phonon modes, ~1.23. The Tc dependence on the profiles of the PDOS peaks is described using the variation of the peaks' frequencies and linewidths in different samples.