Theoretical investigation of potential superconductivity in Sr-doped La₃Ni₂O₇ at ambient pressure

The recent discovery of pressure-induced superconductivity in La₃Ni₂O₇ 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-T_c superconductivity in La₃Ni₂O₇ under ambient conditions. Using density functional theory (DFT) calculations, we systematically investigate the structural and electronic properties of Sr-doped La_3−xSr_xNi₂O₇ (x = 0.25, 0.5, 1) at ambient pressure and identify two dynamically stable phases: La_2.5Sr_0.5Ni₂O₇ and La₂SrNi₂O₇. Our calculations reveal that both phases exhibit metallization of the σ-bonding bands dominated by Ni-d_z² orbitals — a key feature associated with high-T_c superconductivity, as reported in the high-pressure phase of La₃Ni₂O₇. Further analysis using tight-binding models shows that the key hopping parameters in La_2.5Sr_0.5Ni₂O₇ and La₂SrNi₂O₇ closely resemble those of La₃Ni₂O₇ under high pressure, indicating that strong super-exchange interactions between interlayer Ni-d_z² orbitals are preserved. These findings suggest that the doped phases may provide a promising platform for exploring superconductivity, which requires further experimental validation.