Bulk superconductivity up to 96 K in pressurized nickelate single crystals

Recently, the Ruddlesden-Popper bilayer nickelate La₃Ni₂O₇ has emerged as a superconductor with a transition temperature (T_c) of approximately 80 K above 14 GPa (refs. ^1-3). Achieving a higher T_c in nickelate superconductors, along with the synthesis of reproducible high-quality single crystals without relying on high-oxygen-pressure growth conditions, remains a significant challenge^4-7. Here we report superconductivity up to 96 K under high pressure in bilayer nickelate single crystals synthesized at ambient pressure. Energy-dispersive spectroscopy, single-crystal X-ray diffraction, nuclear quadrupole resonance and scanning transmission electron microscopy evidenced high crystal quality of the flux-grown La₂SmNi₂O_7-δ single crystals. La₂SmNi₂O₇ exhibits clear bulk superconductivity, including zero resistivity ( $T_{c,\max }^{\mathrm{onset}}$  = 92 K and $T_{c,\max }^{\mathrm{zero}}$  = 73 K at 21.6 GPa) and the Meissner effect (T_c = 60 K at 20.6 GPa). A low-temperature high-pressure structural study indicates that both monoclinic and tetragonal structures can support superconductivity in this bilayer nickelate. Furthermore, we established a correlation between higher T_c under high pressures and larger in-plane lattice distortion under ambient conditions, corroborated by observing even higher $T_c^{\mathrm{onset}}$ of 96 K in La_1.57Sm_1.43Ni₂O_7-δ. This study overcomes key limitations in growing nickelate superconductor crystals, resolves the crystal structure in the superconducting state and demonstrates an effective pathway towards achieving higher T_c.