Abstract
The pressure-induced high-temperature (T(c)) superconductivity in nickelates La(3)Ni(2)O(7-δ) has sparked significant interest to explore its superconductivity at ambient pressure. Whether the pressure-stabilized tetragonal structure is a prerequisite for achieving nickelate superconductivity at ambient pressure is under hot debate. Here, by post-annealing in high oxygen pressure environment, tetragonal La(3)Ni(2)O(6.92) single crystals are successfully obtained at ambient pressure, which exhibits a metallic behavior without a SDW transition. Moreover, superconductivity is also absent at high pressures up to ~ 70 GPa. Furthermore, by utilizing Helium as the pressure medium, we found that the superconductivity in pressurized orthorhombic La(3)Ni(2)O(6.85) is achieved in orthorhombic structure rather than tetragonal structure claimed previously. All these findings demonstrate that tetragonal structure is not prerequisite for achieving superconductivity in La(3)Ni(2)O(7-δ). Finally, our present work suggests a deep correlation between SDW order and superconductivity, which imposes stringent constraints on the underlying mechanism for pressure-induced superconductivity in nickelates.