Abstract
The partial substitution of Al for Mg in the MgB2 superconductor produces both a progressive reduction of its superconducting transition temperature Tc and the occurrence of two distinct structural phases at low and high Al content, as shown by X-ray diffraction data. To achieve a deeper understanding of the effect of the Al content, we investigated the x dependence of the Raman phonon spectrum in Mg1-xAlxB2 compounds. We analyze the evolution of the E2g Raman-active phonon mode observed on increasing x both in our measurements (0 ≤ x ≤ 0.5) and in recent experiments (0 ≤ x ≤ 1). Our analysis shows the connection between the evolution with x of the E2g phonon and the Tc suppression, thus supporting the hypothesis that superconductivity in MgB2 is mediated by a strong e-ph coupling with the E2g mode. We then derive the electron-phonon coupling constant λ in the 0-0.5 x range.
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