Pressure evolution of crystal structure, magnetism, and electrical resistivity in bilayer and trilayer nickelates*

The recent discovery of superconductivity in bilayer Ruddlesden-Popper nickelate La₃Ni₂O₇, with T_C up to 80 K at pressure above 14 GPa, has generated significant interest in exploring high temperature superconductivity in nickelates. However, considering the structure ambiguity of high pressure phase and the crucial role of the structure-property relationship in understanding the mechanism behind high T_C superconductivity, in this study, we report the high pressure synthesis of bilayer and trilayer Ruddlesden-Popper nickelates, La₃Ni₂O₇ and La₄Ni₃O₁₀, at 20 GPa and 1400 °C. Single crystal X-ray diffraction results reveal lattice compression with subtle structure variations compared to ambient pressure. The evolution of this structural feature under pressure is further explored through in situ high pressure laboratory X-ray single crystal diffraction. We will present our investigation, including the magnetization and electrical resistivity measurements.