High-temperature superconductivity with zero resistance and strange-metal behaviour in La₃Ni₂O₇−δ

摘要

Recent experimental observations have showed some signatures of superconductivity close to 80 K in La₃Ni₂O₇ under pressure and have raised the hope of achieving high-temperature superconductivity in bulk nickelates. However, a zero-resistance state—a key characteristic of a superconductor—was not observed. Here we show that the zero-resistance state does exist in single crystals of La₃Ni₂O₇−δ using a liquid pressure medium at up to 30 GPa. We also find that the system remains metallic under applied pressures, suggesting the absence of a metal–insulator transition proximate to the superconductivity. Moreover, analysis of the normal state T-linear resistance reveals a link between this strange-metal behaviour and superconductivity. The association between strange-metal behaviour and high-temperature superconductivity is very much in line with other classes of unconventional superconductors, including the cuprates and Fe-based superconductors. Further investigations exploring the interplay of strange-metal behaviour and superconductivity, as well as possible competing electronic or structural phases, are essential to understand the mechanism of superconductivity in this system.

材料

• La₃Ni₂O₇-δ

方法

• High-pressure transport measurements using liquid pressure medium

关键词

• zero resistance state
• strange metal behaviour
• t linear resistance
• absence of metal insulator transition

亮点

• The association between strange-metal behaviour and high-temperature superconductivity aligns with cuprates and Fe-based superconductors.

结论

• Zero-resistance state exists in La₃Ni₂O₇−δ single crystals under pressure up to 30 GPa.
• The system remains metallic, suggesting absence of a metal-insulator transition proximate to superconductivity.
• The strange-metal behavior is linked to superconductivity.

主要论断

• Zero-resistance state (superconductivity) exists in La₃Ni₂O₇−δ single crystals under pressure with T_c up to 40 K (zero) and onset ≈66 K.
  • 证据: Fig.1: Clear transition to zero resistance at 20.5 GPa,Reproducible in multiple samples (Fig.2, Extended Data Fig.3),I-V curves show superconducting critical current
• Strange-metal behaviour (T-linear resistance) is closely associated with superconductivity.
  • 证据: Normal state R(T) linear above T_c (Fig.2b dashed green line),Temperature range of T-linear behaviour is largest near maximum T_c (Fig.4b),A' and T_c both decrease with pressure above 20.5 GPa
• Pressure-induced structural transition (Amam to Fmmm) at ≈13 GPa leads to metallization of 3dz2 band and emergence of superconductivity.
  • 证据: Hall coefficient increases sharply above 15 GPa (Fig.4c inset),Low-pressure structural phase has tilted octahedra; high-pressure has untilted,Density wave anomaly in resistance disappears by 2 GPa

研究流程

• Sample synthesis and characterization — Superconductivity is sensitive to oxygen content; zero resistance observed in samples with less oxygen deficiency.
  • 材料: La₃Ni₂O₇−δ single crystals
  • 方法: Growth from same batch as Ref.7; Energy-dispersive X-ray spectroscopy for composition
  • 观察: Samples with large oxygen deficiency do not show superconductivity; Small deficiency samples show zero resistance
• High-pressure electrical transport measurements — Zero-resistance state achieved in La₃Ni₂O₇−δ under high pressure with liquid medium, confirming bulk superconductivity.
  • 材料: La₃Ni₂O₇−δ single crystal
  • 方法: Four-probe resistance in piston-cylinder cell (P<2.5 GPa) and DAC (P>13 GPa); Liquid pressure-transmitting medium for hydrostaticity
  • 观察: At₂₀.5 GPa: T_c onset 66 K, zero resistance at ≈40K; Linear T dependence above T_c (strange metal); Pressure phase diagram: T_c increases to maximum at 20.5 GPa then decreases; dTc/dP ≈ -0.8 K/GPa above 20.5 GPa
• Upper critical field and flux flow analysis — Superconductivity is robust with high upper critical field; flux flow behavior similar to other unconventional superconductors.
  • 材料: Same sample at 20.5 and 26.6 GPa
  • 方法: Resistance in magnetic fields up to 9T; Ginzburg-Landau fitting; Arrhenius plot for thermal activation energy
  • 观察: Hc₂(0) ≈ 97 T (20.5 GPa), 83 T (26.6 GPa); Coherence lengths ≈1.8-2.0 nm; TAFF activation energyU₀(1T)=702 K, weak field dependence U₀∝H-0.12
• Hall effect and phase diagram — Pressure-induced structural transition to Fmmm phase metallizes 3dz2 band, enabling superconductivity.
  • 材料: Same sample
  • 方法: Hall resistivity measurements under pressure
  • 观察: Positive Hall coefficient increases above 15 GPa, indicating increased hole carriers; Metallization of 3dz2 bonding bands due to enhanced interlayer coupling