摘要
The discovery of 80 K superconductivity in pressurized bilayer Ruddlesden-Popper (RP) nickelate La3Ni2O7 has established a new high-temperature superconductor family. The quest to understand the governing principles of RP nickelate superconductivity has become a central focus in condensed matter physics. Here, we report a critical advance by synthesizing and investigating a distinct structural polymorph of the same compound: the monolayer-trilayer (1313) hybrid phase of La3Ni2O7. Under high pressure, synchrotron X-ray diffraction and Raman spectroscopy reveal a structural transition from the orthorhombic Cmmm to the tetragonal P4/mmm space group at 13~GPa. Above 19 GPa, the phase exhibits a clear superconducting transition, confirmed by a zero-resistance state, albeit at a significantly reduced temperature of 3.6 K. The stark contrast with the 80 K transition in the bilayer phase provides a uniquely clean experimental comparison. Our results demonstrate that the superconducting transition temperature is directly governed by the nature of the interlayer coupling, and the bilayer NiO6 block as the essential structural motif for achieving high-Tc superconductivity in the RP nickelates.
材料
方法
关键词
亮点
- Stark contrast in Tc between 1313 and bilayer phases provides clean experimental comparison.
- Superconducting transition temperature directly governed by interlayer coupling nature.
结论
- The 1313 hybrid phase of La3Ni2O7 exhibits superconductivity above 19 GPa with Tc=3.6 K, much lower than the bilayer phase, indicating that bilayer NiO6 block is essential for high Tc.
主要论断
- Superconductivity with Tc onset 3.6 K and zero resistance at 2.3 K is observed in the 1313 phase above 19 GPa.
- 证据: Resistance measurements show sharp drop at 3.6 K at 19.0 GPa and zero resistance at 2.3 K at 24.3 GPa.
- The structural transition from orthorhombic Cmmm to tetragonal P4/mmm occurs at 13 GPa, preceding superconductivity.
- 证据: Synchrotron XRD shows merging of (020) and (200) peaks at 13.4 GPa; Raman shows peak merging at 13.0 GPa.
- The bilayer NiO6 block is the essential structural motif for high-Tc superconductivity in RP nickelates.
- 证据: Comparison of Tc among bilayer (80 K), trilayer (30 K), hybrid 1212 (64 K) and 1313 (3.6 K) phases shows dramatic suppression when bilayer motif is disrupted.
研究流程
- sample_preparation — Successfully synthesized high-purity single crystals of the hybrid 1313 phase.
- 材料: La2O3; NiO; oxygen
- 方法: high-pressure floating-zone method; grinding; sintering
- 观察: High-purity single crystals of hybrid 1313 phase La3Ni2O7 up to 3 cm in length
- ambient_pressure_characterization — Crystal structure and basic electronic/magnetic properties established.
- 材料: 1313La3Ni2O7 single crystals
- 方法: XRD; Laue diffraction; HAADF-STEM; SQUID magnetometry; resistance measurement
- 观察: Orthorhombic Cmmm structure; Metallic resistance with anomalies at 243 K and 185K; Anisotropic magnetic susceptibility; No bilayer phase detected
- high_pressure_transport — Superconductivity emerges above 19 GPa in the 1313 phase with Tc ≈3.6 K.
- 材料: 1313La3Ni2O7 single crystals; Daphne oil 7373
- 方法: diamond anvil cell (DAC); four-probe resistance; PPMS
- 观察: Superconducting transition onset at 3.6 K above 19 GPa; Zero resistance at 2.3 K at 24.3 GPa; Upper critical field ≈1T
- high_pressure_structural_characterization — Structural transition precedes superconductivity at 13 GPa.
- 材料: powder sample; neon gas; helium gas
- 方法: synchrotron XRD; Raman spectroscopy; DAC
- 观察: Structural transition from orthorhombic Cmmm to tetragonal P4/mmm at 13 GPa; Ni-O-Ni angle 180°; Raman peak merging at 13 GPa
- analysis_and_phase_diagram — Bilayer NiO6 block is essential for high-Tc superconductivity in RP nickelates.
- 方法: data analysis; phase diagram construction
- 观察: Phase diagram shows structural transition at 13 GPa and superconductivity above 19 GPa; Comparison with bilayer, trilayer, and other hybrid phases