Motivated by the recently discovered high-$T_c$ superconductor La$_3$Ni$_2$O$_7$, 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 ($\pi$, 0) was stable at the intermediate region. Pairing is induced in the $s_{ \pm}$-wave channel due to partial nesting between the { \bf M}=$(\pi, \pi)$ centered pockets and portions of the Fermi surface centered at the { \bf X}=$(\pi, 0)$ and { \bf Y}=$(0, \pi)$ points. This resembles results for iron-based superconductors but has a fundamental difference with iron pnictides and selenides. Moreover, our present efforts also suggest that La$_3$Ni$_2$O$_7$ is qualitatively different from infinite-layer nickelates and cuprate superconductors.
Categories: cond-mat.supr-con