Identification of superconductivity in bilayer nickelate La₃Ni₂O₇ under high pressure up to 100 GPa

Summary

Identification of superconductivity in the Ruddlesden-Popper phases of nickelates under high pressure remains challenging. Here, we report a comprehensive study of the crystal structure, electrical resistance, and Meissner effect in single crystals of bilayer nickelate La₃Ni₂O₇ under hydrostatic pressures up to 104 GPa. Using high-pressure X-ray diffraction, we observe a structural transition from an orthorhombic to a tetragonal phase above 40 GPa. Superconductivity emerges with a maximum onset transition temperature Tconset of 83 K at 18.0 GPa, accompanied by zero resistance. The superconducting phase is gradually suppressed and vanishes above 80 GPa, forming a right-triangle-like superconducting region. Direct-current magnetic susceptibility measurements demonstrate the Meissner effect and reveal a superconducting volume fraction of ∼41% at 22.0 GPa and 20 K, confirming the bulk nature of superconductivity in La₃Ni₂O₇. Our results highlight the intricate relationship between superconductivity, oxygen content, and structural transitions in this material.

Materials

• La₃Ni₂O₇

Methods

• High-pressure X-ray diffraction
• Electrical resistance measurements
• Direct-current magnetic susceptibility measurements

Keywords

• structural transition
• meissner effect
• superconducting volume fraction
• right triangle like superconducting region

Highlights

• Bulk nature of superconductivity confirmed by Meissner effect.
• Intricate relationship between superconductivity, oxygen content, and structural transitions.

Conclusions

• Superconductivity emerges with maximum onset T_c of 83 K at 18 GPa, accompanied by zero resistance.
• Superconducting phase is suppressed above 80 GPa, forming a right-triangle-like region.
• Meissner effect confirms bulk superconductivity with volume fraction of ≈41%.

Main claims

• Superconductivity with maximum onset T_c of 83 K is observed in La₃Ni₂O₇ under high pressure.
  • Evidence: Resistance measurements show a drop with zero resistance at 18.0 GPa (Fig. 2d)
• Bulk superconductivity is confirmed by the Meissner effect with a superconducting volume fraction of about 41%.
  • Evidence: DC magnetic susceptibility measurements show diamagnetic signal at 22.0 GPa and 20 K (Fig. 3b-d)
• A structural transition from orthorhombic to tetragonal symmetry occurs above 40 GPa.
  • Evidence: Synchrotron XRD patterns show merging of peaks indicating transition to I₄/mmm (Fig. 1b)

Workflow

• sample_preparation — High-quality samples with consistent bilayer structure were obtained for pressure studies.
  • Materials: Polycrystalline La₃Ni₂O₇ (sol-gel); Single-crystal La₃Ni₂O₇ (floating zone)
  • Methods: Sol-gel method; High-pressure floating zone method
  • Observations: All samples confirmed bilayer RP phase structure
• high_pressure_synchrotron_xrd — Crystal structure evolves with pressure; tetragonal phase appears above 40 GPa.
  • Materials: Polycrystalline La₃Ni₂O₇
  • Methods: Synchrotron XRD with neon gas as pressure transmitting medium
  • Observations: Structural transition from orthorhombic (Amam) to orthorhombic (Fmmm) at 12.3 GPa; Transition to tetragonal (I₄/mmm) above 46.8 GPa
• high_pressure_electrical_transport — Superconductivity with maximum Tc_onset of 83 K and zero resistance exists under pressure.
  • Materials: Single-crystal La₃Ni₂O₇
  • Methods: Diamond anvil cell with KBr as pressure transmitting medium; Four-probe resistance measurement
  • Observations: Superconductivity emerges with onset T_c up to 83 K at 18.0 GPa; Zero resistance observed in multiple runs; Superconductivity suppressed above 80 GPa
• high_pressure_dc_magnetic_susceptibility — Bulk nature of superconductivity confirmed by Meissner effect.
  • Materials: Single-crystal La₃Ni₂O₇
  • Methods: Miniature diamond anvil cell with helium as pressure transmitting medium; MPMS measurement
  • Observations: Meissner effect observed; Superconducting volume fraction ≈41%
• phase_diagram_construction — Superconducting phase diagram shows a dome-like region.
  • Materials: Data from transport and XRD
  • Methods: Compilation of T_c and structural data
  • Observations: Right-triangle-like superconducting region; Maximum T_c at ≈18 GPa, suppressed above 80 GPa