Ambient-pressure insulator-to-metal transition in bulk La3Ni2O7 via Lu doping

The recent discovery of high-temperature superconductivity near 80 K under high pressure in the bulk form of bilayer nickelate La₃Ni₂O₇ has intensified efforts to stabilize analogous electronic states at ambient pressure. Here, we investigate chemical doping as a route to tuning the ground state of bulk La₃Ni₂O₇ by substituting La³⁺ with smaller rare-earth (R) ions. Through systematic synthesis and electrical transport measurements of R-doped La₃Ni₂O₇ (R = Y, Nd, Dy, Lu), we find that Y, Nd, and Dy substitutions retain the semiconducting behavior of the parent compound. Strikingly, doping with the heaviest rare-earth element, lutetium (Lu), induces an ambient-pressure insulator-to-metal transition. This result highlights the critical role of chemical pressure in modifying electronic correlations and demonstrates that targeted ion substitution can access emergent quantum phases in nickelates without applied physical pressure. Our work establishes chemical doping as a versatile strategy for exploring and controlling exotic electronic states in correlated nickelate systems. Complementarily, high-pressure measurements reveal that chemical doping fundamentally alters the system's quantum response, highlighting the synergy of both approaches for accessing diverse quantum phases.