Structural phase transition, s _±-wave pairing, and magnetic stripe order in bilayered superconductor La ₃Ni ₂O ₇ under pressure

Abstract

Motivated by the recently discovered high- T _c superconductor La ₃Ni ₂O ₇, we comprehensively study this system using density functional theory and random phase approximation calculations. At low pressures, the Amam phase is stable, containing the Y ²⁻ mode distortion from the Fmmm phase, while the Fmmm phase is unstable. Because of small differences in enthalpy and a considerable Y ²⁻ mode amplitude, the two phases may coexist in the range between 10.6 and 14 GPa, beyond which the Fmmm phase dominates. In addition, the magnetic stripe-type spin order with wavevector ( π, 0) was stable at the intermediate region. Pairing is induced in the s _±-wave channel due to partial nesting between the M = ( π,  π) centered pockets and portions of the Fermi surface centered at the X = ( π, 0) and Y = (0,  π) points. This resembles results for iron-based superconductors but has a fundamental difference with iron pnictides and selenides. Moreover, our present efforts also suggest La ₃Ni ₂O ₇ is qualitatively different from infinite-layer nickelates and cuprate superconductors.

Abstract

Recently superconductivity with T _c of about 80 K was discovered in a bilayer nickelate La ₃Ni ₂O ₇ under high pressure. Here the authors report a density functional theory and random phase approximation study of structural and electronic properties as a function of pressure and discuss the pairing mechanism.