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VOLUME 75 (2002) | ISSUE 8 | PAGE 479
Raman spectra of MgB2 at high pressure and topological electronic transition
PACS: 74.62.Fj, 74.25.Kc, 74.25.Gz
Abstract
Raman spectra of the MgB2 ceramic samples were measured as a function of pressure up to 32 GPa at room temperature. The spectrum at normal conditions contains a very broad peak at \sim590 cm-1 related to the E2g phonon mode. The frequency of this mode exhibits a strong linear dependence in the pressure region from 5 to 18 GPa, whereas beyond this region the slope of the pressure-induced frequency shift is reduced by about a factor of two. The pressure dependence of the phonon mode up to \sim5 GPa exhibits a change in the slope as well as a "hysteresis" effect in the frequency vs. pressure behavior. These singularities in the E2g mode behavior under pressure support the suggestion that MgB2 may undergo a pressure-induced topological electronic transition.