High-temperature superconductivity in Nd₀.85Sr₀.15NiO₂ membranes under pressure

摘要

研究人员开发了一种将自由站立无限层Nd₀.₈₅Sr₀.₁₅NiO₂薄膜集成到金刚石对顶砧中的技术，从而克服了薄膜在高压环境中测量的困难。通过对该薄膜施加高达约90 GPa的压力，他们观测到超导转变温度（T_c）从常压下的约17 K单调线性提升至约74.2 K，增强速率约为0.65 K/GPa，且未出现饱和迹象。这一线性的、非饱和的T_c压力演化趋势与大多数铜氧化物超导体及双层镍酸盐中观察到的压力诱导过掺杂导致的T_c下降行为显著不同，表明无限层镍酸盐的配对强度可被提升至出乎意料的高水平。此外，上临界场和相干长度的测量进一步证实了超导态随压力增强。该研究提供了通过晶格压缩持续增强超导电性的新途径，且所开发的自由薄膜高压技术有望广泛应用于其他二维材料。

材料

• Nd₀.85Sr₀.15NiO₂
• Nd₀.85Sr₀.15NiO₂

方法

• high-pressure transport
• diamond anvil cell (DAC)
• transport measurements

关键词

• linear pressure dependence
• tc enhancement
• london penetration depth
• coherence length
• high temperature superconductivity
• pressure enhancement of tc
• pairing strength

亮点

• The linear, non-saturating pressure dependence of T_c differs from the pressure-induced overdoping that suppresses T_c in cuprates and bilayer nickelates.
• The pairing strength in infinite-layer nickelates can be elevated to unexpectedly high levels.
• Developed a technique to incorporate freestanding infinite-layer Nd₀.85Sr₀.15NiO₂ membranes into a diamond anvil cell, enabling high-pressure measurements on thin films.

结论

• The superconducting transition temperature increases linearly with pressure at a rate of 0.65 K/GPa, reaching ≈74.2 K at 90 GPa with no signs of saturation.
• The upper critical field and coherence length confirm pressure-induced enhancement of the superconducting state.
• T_c increases linearly with pressure at a rate of 0.65 K GPa-1 up to ≈90 GPa, with no signs of saturation.
• The pairing strength in infinite-layer nickelates can be raised to a surprisingly high scale.

主要论断

• The superconducting transition temperature in Nd₀.85Sr₀.15NiO₂ infinite-layer membranes increases linearly with pressure at a rate of 0.65 K/GPa, reaching 74.2 K at 91.5 GPa without saturation
  • 证据: Transport measurements on six samples show consistent linear T_c(P) dependence; no sign of saturation up to highest pressure
• T_c increases linearly with pressure at a rate of 0.65 K GPa^-1, showing no signs of saturation up to ≈90 GPa.
  • 证据: Abstract: 'Strikingly, we find a simple linear enhancement of T_c at a rate of 0.65 K GPa^-1, with no signs of saturation.',Full text: 'Figure 3 compiles the pressure dependence T_c(P) for all six measured samples, which are remarkably consistent. The data are well described by a line with slope dTc/dP ≈ 0.65 K GPa^-1.'
• At₉₁.5 GPa, the superconducting transition onset reaches ≈74.2 K, near liquid nitrogen temperature.
  • 证据: Abstract: 'a superconducting downturn can be observed near liquid nitrogen temperatures.',Full text: 'R(T) at P = 91.5 GPa, showing T_c,onset ≈ 74.2 K',Full text: 'T_c,onset, 99.5% = 74.2 K' (Extended Data Fig. 1)

研究流程

• Freestanding membrane preparation — Robust superconductivity preserved in freestanding form
  • 材料: Nd₀.85Sr₀.15NiO₂ thin films with SrTiO₃ cap
  • 方法: PLD; Water etching of sacrificial layer; Cryogenic UHV transfer
  • 观察: Superconducting membranes
• High-pressure assembly
  • 材料: Diamond anvil cell (DAC)
  • 方法: Electrode fabrication via stencil mask; cBN insulating gasket
  • 观察: Resistance measured as function of temperature and pressure
• Transport measurements — Pressure enhances T_c significantly without saturation
  • 方法: Four-probe resistance; Upper critical field extraction
  • 观察: T_c increases linearly with pressure at ≈0.65 K/GPa; No saturation up to 74.2 K at 91.5 GPa; Coherence length decreases
• sample_preparation_and_dac_integration — Freestanding infinite-layer nickelate membranes can be integrated into a diamond anvil cell for high-pressure transport.
  • 材料: Nd₀.85Sr₀.15NiO₂ thin film (≈6.7 nm); SrTiO₃ capping layers; Sr₂Ca₁Al₂O₆ sacrificial layer; Silicone oil (pressure-transmitting medium); Pt foil; cBN powder
  • 方法: Pulsed laser deposition; Topotactic reduction; Water etching of sacrificial layer; Transfer to diamond culet; Stencil mask lithography; Ion milling and e-beam evaporation of Ti/Au contacts
  • 观察: Freestanding membrane superconducts at ambient with T_c ≈17K; Uniform electrical contacts achieved
• high_pressure_transport_characterization — Pressure drives a strong linear enhancement of T_c without saturation, reaching near liquid-nitrogen temperatures.
  • 材料: Membrane in DAC; Silicone oil PTM; Ruby chips (pressure calibration)
  • 方法: Diamond anvil cell (200–300 μm culets); Four-probe electrical resistance measurement; Pressure calibration via ruby fluorescence and diamond Raman edge; Magnetic field up to 13T
  • 观察: T_c increases linearly: dTc/dP = 0.65 K GPa^-1; At₉₁.5 GPa, T_c,onset = 74.2K; Coherence length ξab decreases from 2.39 nm (ambient) to 1.54 nm (71.8 GPa); No saturation of T_c up to max pressure