Prediction of several Co-based La$_3$Ni$_2$O$_7$-like superconducting materials

Abstract

High-temperature superconductivity has been found in Fe-, Ni-, and Cu-based compounds but has remained elusive in Co-based materials. The recent discovery of superconductivity in pressurized bilayer nickelate La$_3$Ni$_2$O$_7$ has renewed interest in related layered systems. Here, we predict several Co-based analogs that may realize similar physics. Electron doping of the high-pressure bilayer cobaltate La$_3$Co$_2$O$_7$ yields LaTh$_2$Co$_2$O$_7$, La$_3$Ni$_2$O$_5$Cl$_2$, and La$_3$Ni$_2$O$_5$Br$_2$, which exhibit closely related crystal structures and strongly correlated electronic states. Random-phase-approximation calculations reveal $s$-wave as the leading pairing symmetry in these compounds.

Figures (4)

• Figure 1: Crystal structure of (a) LNO, (b) LCO, (c) LCO-Th, and (d) LCO-Cl at high pressure.
• Figure 2: Band structures of LNO, LCO-Th, and LCO-Cl. The DFT bands are shown in the upper panels. The band structure of the fitted bilayer two-orbital tight-binding models is superposed, where the orbital weights are represented by the size of the colored circles. The momentum-resolved spectral functions $A(\mathbf{k},\omega)$ obtained by DFT+DMFT at 290 K are displayed in the lower panels. The dashed green and blue lines at 0 eV denote the Fermi level.
• Figure 3: The imaginary parts of the self-energies $\rm{Im}\Sigma(i\omega_n)$ at the Matsubara axis for LNO, LCO-Th, and LCO-Cl at 290 K.
• Figure 4: The upper panels show the orbital-resolved Fermi surfaces of the corresponding TB models for (a) LNO, (b) LCO-Th, and (c) LCO-Cl. The lower panels show the superconducting gap structures on the Fermi surfaces calculated with RPA on the three TB models with $U=1.4$, $0.9$, and $1$ eV, respectively.