Anharmonicity and self-energy effects of E2g phonon in MgB2

We present Raman scattering study on the E2g phonon anharmonicity and on superconductivity induced self-energy effects in MgB2 single crystals. We show that anharmonic two phonon decay is mainly responsible for the unusually large line width of the E2g mode. We observed 2.5%hardening of the E2g phonon frequency upon cooling into superconducting state and we estimate electron-phonon coupling strength associated with this renormalization.