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

Abstract

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 La_3Ni_2O_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 $$3{d}_{{x}^{2}-{y}^{2}}$$ 3 d x 2 − y 2 and $$3{d}_{{z}^{2}}$$ 3 d 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 $$3{d}_{{z}^{2}}$$ 3 d 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. Signatures of superconductivity in single crystals of La_3Ni_2O_7 were observed at a maximum transition temperature of 80 K at pressures between 14.0 GPa and 43.5 GPa.