Signatures of superconductivity near 80 K in a nickelate under high pressure

lthough high-transition-temperature (high- T c ) superconductivity in cuprates has been known for more than three decades, the underlying mechanism remains unknown 1 – 4 . Cuprates are the only unconventional superconductors that exhibit bulk superconductivity with T c above the liquid-nitrogen boiling temperature of 77 K. Here we observe that high-pressure resistance and mutual inductive magnetic susceptibility measurements showed signatures of superconductivity in single crystals of La 3 Ni 2 O 7 with maximum T c of 80 K at pressures between 14.0 GPa and 43.5 GPa. The superconducting phase under high pressure has an orthorhombic structure of Fmmm space group with the 3d_x^2-y^2 and 3d_z^2 orbitals of Ni cations strongly mixing with oxygen 2 p orbitals. Our density functional theory calculations indicate that the superconductivity emerges coincidently with the metallization of the σ-bonding bands under the Fermi level, consisting of the 3d_z^2 orbitals with the apical oxygen ions connecting the Ni–O bilayers. Thus, our discoveries provide not only important clues for the high- T c superconductivity in this Ruddlesden–Popper double-layered perovskite nickelates but also a previously unknown family of compounds to investigate the high- T c superconductivity mechanism.