Characterisation of MgB2 thin films of varying Tc by Raman spectroscopy

Raman spectra of a series of thin films of the superconductor MgB₂ have been measured as a function of the T_c of the films. An interesting correlation is observed between the Raman shift of the E_{2 g} mode and the T_c. We propose a mechanism for the T_c reduction, which has consequences for the behaviour of the two superconducting gaps in MgB₂ for samples of very reduced T_c (≤19 K). Additionally, the effects of oxygenation on the properties of MgB₂ have been studied in order to develop an understanding of the effects of structural distortion in this material.