First-principles study of the superconductivity in LaO

A recent experiment reported the first rare-earth binary oxide superconductor LaO (${T}_{c}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) with a rock-salt structure [K. Kaminaga et al., J. Am. Chem. Soc. 140, 6754 (2018)]. Correspondingly, the underlying superconducting mechanism in LaO needs theoretical elucidation. Based on first-principles calculations on the electronic structure, lattice dynamics, and electron-phonon coupling of LaO, we show that the superconducting pairing in LaO belongs to the conventional Bardeen-Cooper-Schrieffer (BCS) type. Remarkably, the electrons and phonons of the heavy La atoms, instead of those of the light O atoms, contribute most to the electron-phonon coupling. We further find that both the biaxial tensile strain and the pure electron doping can enhance the superconducting ${T}_{c}$ of LaO. With the synergistic effect of electron doping and tensile strain, the ${T}_{c}$ could be even higher, for example, 11.11 K at a doping of 0.2 electrons per formula unit and a tensile strain of $4%$. Moreover, our calculations show that the superconductivity in LaO thin film remains down to the trilayer thickness with a ${T}_{c}$ of 1.4 K.