Anharmonicity and self-energy effects of the E-2g phonon in MgB2

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.