Discovery of high-Tc superconductivity in bilayer La3Ni2O7

High-transition-temperature (high-Tc) superconductivity in cuprates has been discovered for over three decades, but the underlying mechanism remains a mystery. Cuprates are the only unconventional superconducting family that hosts 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[3,4]. The superconducting phase under high pressure exhibits a tetragonal structure with the 3dx2-y2 and 3dz2 orbitals of Ni cations mixing with the 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. TEM and inelastic neutron scattering measurements reveal the important role of oxygen on the inner apical site[5,6]. The discoveries reveal important clues for the high-Tc superconductivity in this Ruddlesden-Popper double-layered perovskite nickelates and provide a new family of compounds to investigate the high-Tc superconductivity mechanism.