Bulk superconductivity up to 96 K in pressurized nickelate single crystals

摘要

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 challenge4–7. 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 La₂SmNi₂O₇−δ single crystals. La₂SmNi₂O₇ exhibits clear bulk superconductivity, including zero resistivity (T_rmc,max ^rmonset = 92 K and T_rmc,max ^rmzero = 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_rmc^rmonsetof 96 K in La₁.57Sm₁.43Ni₂O₇−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.

材料

• La₂SmNi₂O₇-δ
• La₁.57Sm₁.43Ni₂O₇-δ

方法

• Flux method
• Energy-dispersive spectroscopy
• Single-crystal X-ray diffraction
• NQR
• STEM
• High-pressure measurements

关键词

• bulk superconductivity
• meissner effect
• in plane lattice distortion

亮点

• Correlation between higher T_c under high pressures and larger in-plane lattice distortion under ambient conditions.
• Overcomes key limitations in growing nickelate superconductor crystals.

结论

• Bulk superconductivity with zero resistance and Meissner effect is observed in La₂SmNi₂O₇−δ single crystals.
• Higher T_c up to 96 K is achieved in La₁.57Sm₁.43Ni₂O₇−δ.

主要论断

• La₂SmNi₂O₇-δ exhibits bulk superconductivity with zero resistivity (Tc_onset=92 K, Tc_zero=73 K) and Meissner effect under high pressure.
  • 证据: Resistivity shows sharp zero-resistance transition (Fig. 3a-c),DC susceptibility shows diamagnetic signal with >60% shielding fraction (Fig. 3e, Extended Data Fig. 6)
• Both monoclinic (P₂₁/m) and tetragonal (I₄/mmm) crystal structures can host superconductivity.
  • 证据: Low-temperature XRD shows monoclinic phase at 17.9 GPa and 64 K, which is in the superconducting state (Fig. 4d)
• The highest T_c in nickelates is achieved at 96 K (Tc_onset) in La₁.57Sm₁.43Ni₂O₇-δ under pressure.
  • 证据: Resistance measurements show onset T_c of 96 K at 21.6 GPa (Extended Data Fig. 10h)
• Higher T_c under high pressure correlates with larger in-plane lattice distortion at ambient conditions.
  • 证据: T_c increases with Δ across La₃Ni₂O₇, La₂PrNi₂O₇, La₂SmNi₂O₇, and La₁.57Sm₁.43Ni₂O₇ (Fig. 5a)

研究流程

• single_crystal_growth — High-quality bilayer single crystals grown at ambient pressure.
  • 材料: La₂O₃; Sm₂O₃; NiO; K₂CO₃ flux
  • 方法: Ambient pressure flux method
  • 观察: Large La₂SmNi₂O₇-δ single crystals up to 220 µm
• crystal_quality_evaluation — La₂SmNi₂O₇-δ single crystals exhibit excellent crystallinity and near-stoichiometric oxygen content.
  • 材料: As-grown and annealed single crystals
  • 方法: EDS mapping; SXRD; NQR; STEM-HAADF; TGA
  • 观察: High homogeneity; No intergrowth; Preferential Sm occupancy; Oxygen content δ≈0.00(2) after annealing
• high_pressure_resistivity_and_meissner_effect — Bulk superconductivity with record T_c up to 96 K in pressurized nickelates.
  • 材料: Annealed La₂SmNi₂O₇-δ single crystals; La₁.57Sm₁.43Ni₂O₇-δ single crystals
  • 方法: DAC with helium as PTM; Four-probe resistivity; DC magnetic susceptibility with miniature DAC
  • 观察: Tc_onset=92 K, Tc_zero=73 K at 21.6 GPa in La₂SmNi₂O₇; Meissner effect with >60% volume fraction; Tc_onset=96 K in La₁.57Sm₁.43Ni₂O₇
• high_pressure_low_temperature_xrd — Both monoclinic and tetragonal structures support superconductivity.
  • 材料: Pulverized La₂SmNi₂O₇ single crystals
  • 方法: Synchrotron XRD with helium PTM; In situ cryostat
  • 观察: Monoclinic phase at 17.9 GPa down to 64 K in superconducting state; Tetragonal phase at higher pressures
• phase_diagram_and_correlation_analysis — Ambient-pressure lattice distortion is a useful indicator for achieving higher T_c under pressure.
  • 材料: Transport and structural data from multiple samples
  • 方法: Compilation; Comparison with literature
  • 观察: Strange metal behavior above T_c; T_c increases with ambient-pressure in-plane lattice distortion; Highest T_c in La₁.57Sm₁.43Ni₂O₇