Investigation of superconductivity in ultrahigh pressure phases of yttrium

Abstract

The superconductivity of yttrium metal under high pressure were systematically investigated by utilizing first-principles calculations. Based on the evolutionary structure searches, we have proposed a new ultrahigh pressure phase of C2/m that is energetically competitive to the previously reported Fmm2. The electron-phonon coupling calculations demonstrated a Tc of 16.97 K at 700 GPa in our proposed C2/m, whereas the Tc in Fmm2 was estimated to be 12.19–9.46 K in the pressure range of 600–800 GPa accompanied by a declining trend upon compression. Further analyses of Fermi surface nesting functions reveal that the shrinking Tc in Fmm2 is dominated by phonon frequencies and N(εF), while the difference of Tc's between C2/m and Fmm2 is mainly attributed to the tremendous difference of electron-phonon matrix element. Our findings would offer fundamental insights for understanding the superconducting mechanism in yttrium and even other rare earth superconductors under BCS framework.