Pressure-Induced Superconductivity In Polycrystalline La3Ni2O7-δ

We synthesized polycrystalline La3Ni2O7-δ (δ ≈ 0.07) samples by using the sol-gel method without postannealing under high oxygen pressure, and then measured temperature-dependent resistivity under various hydrostatic pressures up to 18 GPa by using the cubic anvil and two-stage multianvil apparatus. We find that the density-wave-like anomaly in resistivity is progressively suppressed with increasing pressure and the resistivity drop corresponding to the onset of superconductivity emerges at pressure as low as ~ 6 GPa. Zero resistivity is achieved at 9 GPa below $T^{ZERO}_{c}$ ≈ 6.6 K, which increases quickly with pressure to 41 K at 18 GPa. However, the diamagnetic response was not detected in the ac magnetic susceptibility measurements up to 15 GPa, indicating a filamentary nature of the observed superconductivity in the studied pressure range. The constructed $T$-$P$ phase diagram reveals an intimate relationship between superconductivity, density-wave-like order, and the strange-metal-like behaviors. The observation of zero-resistance state in the polycrystalline La3Ni2O7-δ samples under high pressures not only corroborates the recent report of superconductivity in the pressurized La3Ni2O7 crystals but also facilitates further studies on this emerging family of nickelate high-$T$c superconductors.