High-transition-temperature (high-Tc) superconductivity in cuprates has been discovered for more than three decades, but the underlying mechanism remains a mystery. Cuprates are the only unconventional superconducting family that host bulk superconductivity with Tcs above the liquid nitrogen boiling temperature at 77 Kelvin. We found superconductivity in single crystals of La3Ni2O7 grown by the high-pressure floating zone method with a maximum Tc of 80 K at pressures between 14.0-43.5 gigapascals [1,2]. Our collaborators have confirmed the high Tc superconductivity on our samples independently [3,4]. The superconducting phase under high pressure exhibits an orthorhombic structure of Fmmm space group with the 3dx2-y2 and 3dz2 orbitals of Ni cations strongly mixing with oxygen 2p orbitals. Density functional theory calculations suggest the superconductivity emerges coincidently with the metallization of the σ-bonding bands under the Fermi level, consisting of the 3dz2 orbitals with the apical oxygens connecting Ni-O bilayers. Thus, the discoveries not only reveal important clues for the high-Tc superconductivity in this Ruddlesden-Popper double-layered perovskite nickelates but also provide a new family of compounds to investigate the high-Tc superconductivity mechanism.
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