Pressure dependence of the Raman spectrum, lattice parameters and superconducting critical temperature of MgB2:: evidence for pressure-driven phonon-assisted electronic topological transition

We overview recent high-pressure studies of high-temperature superconductor MgB2 by Raman scattering technique combined with measurements of superconducting critical temperature T-c and lattice parameters up to 57 GPa. An anomalously broadened Raman band at 620 cm(-1) is observed and assigned to the in-plane boron stretching E-2g mode. It exhibits a large Gruneisen parameter indicating that the vibration is highly anharmonic. The pressure dependencies of the E-2g mode and T-c reveal anomalies at 15-22 GPa (isotope dependent). The anharmonic character of the E-2g phonon mode, its anomalous pressure dependence, and also that for T-c are interpreted as a result of a phonon-assisted Lifshitz electronic topological transition. (C) 2002 Elsevier Science B.V. All rights reserved.