Mg-doping induced fluorine-based superconductor MgF5 under high pressure

Abstract

Exploring novel superconductors is a crucial topic in condensed matter physics. There are few reports on the superconductivity of fluorine due to the extremely high pressures required for its metallization. Here, metallization and superconductivity of fluorine were achieved in MgF₅ at 120 GPa by exploiting the high-pressure s-d transition of doped Mg. The unexpected Mg-F covalent bonding induced by Mg-d and F-p orbital interactions led to fluorine metallization and the formation of an F skeleton similar to a H-cage. The high density of states (DOS) from the F skeleton and phonon softening from strong Fermi surface nesting contribute to a high superconducting transition temperature (T_c). The T_c of Pmmm-MgF₅ at 120 GPa is 14.02 K, with strong electron–phonon coupling (λ = 0.84), which is close to that of Li₆P at 270 GPa (λ = 1.01). This is the first observation of superconductivity in main-group metal fluorides. Additionally, two near-monatomic F atoms exist in the interstitial region of MgF₅, significantly enhancing electron–phonon coupling. This work challenges the traditional view of main-group metal fluorides and provides deeper insights into the superconductivity and physicochemical properties of fluorine.

Graphic abstract