Theoretical Investigation of High-Tc Superconductivity in Sr-Doped La${}_3$Ni${}_2$O${}_7$ at Ambient Pressure

Abstract

The recent discovery of pressure-induced superconductivity in La${}_3$Ni${}_2$O${}_7$ has established a novel platform for studying unconventional superconductors. However, achieving superconductivity in this system currently requires relatively high pressures. In this study, we propose a chemical pressure strategy via Sr substitution to stabilize high-Tc superconductivity in La${}_3$Ni${}_2$O${}_7$ under ambient conditions.Using density functional theory (DFT) calculations, we systematically investigate the structural and electronic properties of Sr-doped La${}_{3-x}$Sr${}_x$Ni${}_2$O${}_7$ (x = 0.25, 0.5, 1) at ambient pressure and identify two dynamically stable phases:La${}_{2.5}$Sr${}_{0.5}$Ni${}_2$O${}_7$ and La${}_2$SrNi${}_2$O${}_7$.Our calculations reveal that both phases exhibit metallization of the $\sigma$-bonding bands dominated by Ni-d${}_{z^2}$ orbitals-a key feature associated with high-Tc superconductivity, as reported in the high-pressure phase of La${}_3$Ni${}_2$O${}_7$. Further analysis using tight-binding models shows that the key hopping parameters in La${}_{2.5}$Sr${}_{0.5}$Ni${}_2$O${}_7$ and La${}_2$SrNi${}_2$O${}_7$ closely resemble those of La${}_3$Ni${}_2$O${}_7$ under high pressure, indicating that strong super-exchange interactions between interlayer Ni-d${}_{z^2}$ orbitals are preserved. These findings suggest that Sr-doped La${}_3$Ni${}_2$O${}_7$ is a promising candidate for realizing high-Tcsuperconductivity at ambient pressure.