We carried out Raman measurements on neutron-irradiated and Al-doped MgB2 samples. The irradiation-induced topological disorder causes an unexpected appearance of high frequency spectral structures, similar to those observed in lightly Al-doped samples. Our results show that disorder-induced violations of the selection rules are responsible for the modification of the Raman spectrum in both irradiated and Al-doped samples. Theoretical calculations of the phonon density of states support this hypothesis, and demonstrate that the high frequency structures arise mostly from contributions at q=0 of the E2g phonon mode.
@article{arxiv.cond-mat/0602506,
title = {Tuning topological disorder in MgB$_{2}$},
author = {D. Di Castro and E. Cappelluti and M. Lavagnini and A. Sacchetti and A. Palenzona and M. Putti and P. Postorino},
journal= {arXiv preprint arXiv:cond-mat/0602506},
year = {2015}
}