High-pressure anomaly in the normal state of MgB₂

Abstract

The E_2g mode phonon frequency anomaly, observed in high-pressure Raman measurements for the high-temperature superconductor MgB₂ and conjectured to arise due to a phonon-assisted electronic topological transition (ETT), has been corroborated by us with the details of electronic structure calculations of this compound. The present studies have been carried out with a B-atom displacement of the frozen-in E_2g-mode phonon that mimics the effects of thermal vibrations. We found a splitting of the doubly degenerate σ band along the Γ-A direction. The splitting of the band reduces with pressure, causing an ETT at 18 GPa. This ETT is expected to cause anomaly in the E_2g phonon mode by influencing the ionic system. Our calculated electron-phonon coupling constant λ , for the distorted lattice with a frozen-in displacement, also depicts an anomalous variation around 18 GPa.