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

Although 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 La3Ni2O7 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(x2-y2) and 3d(z2)orbitals of Ni cations strongly mixing with oxygen 2p orbitals. Our density functional theory calculations indicate that the superconductivity emerges coincidently with the metallization of the sigma-bonding bands under the Fermi level, consisting of the 3d(z2) orbitals with the apical oxygen ions connecting the Ni-O bilayers. Thus, our discoveries provide not only important clues for the high-Tc 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.