We present a Raman scattering study of the E-2g phonon anharmonicity and of superconductivity-induced self-energy effects in MgB2 single crystals. We show that anharmonic two-phonon decay is mainly responsible for the unusually large linewidth of the E-2g mode. We observe similar to 2.5 hardening of the E-2g phonon frequency upon cooling into the superconducting state and estimate the electron-phonon coupling strength associated with this renormalization.
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