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

Summary

Researchers have developed a technique to integrate free-standing infinite-layer Nd₀.₈₅Sr₀.₁₅NiO₂ thin films into diamond anvil cells, thereby overcoming the difficulties of measuring such films under high-pressure conditions. B_y applying pressures up to approximately 90 GPa to the films, they observed that the superconducting transition temperature (T_c) increased monotonically and linearly from about 17 K at ambient pressure to roughly 74.2 K, with an enhancement rate of approximately 0.65 K/GPa and no signs of saturation. This linear, non-saturating pressure dependence of T_c markedly differs from the pressure-induced overdoping that leads to T_c suppression in most copper oxide superconductors and bilayer nickelates, suggesting that the pairing strength in infinite-layer nickelates can be elevated to unexpectedly high levels. Furthermore, measurements of the upper critical field and coherence length confirm the pressure-induced enhancement of the superconducting state. This study provides a new pathway for continuously enhancing superconductivity through lattice compression, and the developed free-film high-pressure technique holds promise for broad application to other two-dimensional materials.

Materials

• Nd₀.85Sr₀.15NiO₂
• Nd₀.85Sr₀.15NiO₂

Methods

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

Keywords

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

Highlights

• 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.

Conclusions

• 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.

Main claims

• 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
  • Evidence: 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.
  • Evidence: 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.
  • Evidence: 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)

Workflow

• Freestanding membrane preparation — Robust superconductivity preserved in freestanding form
  • Materials: Nd₀.85Sr₀.15NiO₂ thin films with SrTiO₃ cap
  • Methods: PLD; Water etching of sacrificial layer; Cryogenic UHV transfer
  • Observations: Superconducting membranes
• High-pressure assembly
  • Materials: Diamond anvil cell (DAC)
  • Methods: Electrode fabrication via stencil mask; cBN insulating gasket
  • Observations: Resistance measured as function of temperature and pressure
• Transport measurements — Pressure enhances T_c significantly without saturation
  • Methods: Four-probe resistance; Upper critical field extraction
  • Observations: 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.
  • Materials: Nd₀.85Sr₀.15NiO₂ thin film (≈6.7 nm); SrTiO₃ capping layers; Sr₂Ca₁Al₂O₆ sacrificial layer; Silicone oil (pressure-transmitting medium); Pt foil; cBN powder
  • Methods: 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
  • Observations: 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.
  • Materials: Membrane in DAC; Silicone oil PTM; Ruby chips (pressure calibration)
  • Methods: 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
  • Observations: 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