Non-Fermi liquid behavior in La₃Ni₂O₇ thin films under hydrostatic pressure

Summary

This study reports the transport properties of epitaxial bilayer La₃Ni₂O₇ thin films grown on LaAlO₃(001) and SrLaAlO₄(001) substrates, modulated by high-pressure oxygen annealing and hydrostatic pressure. Under ambient pressure, films on LaAlO₃ substrates exhibit Fermi liquid metallic behavior with a slight Kondo-like upturn at low temperatures; upon applying hydrostatic pressure from 0.53 to 1.41 GPa, the temperature dependence of resistance gradually evolves into non-Fermi liquid behavior, approaching approximately ~T¹⁴ at 1.41 GPa. Notably, this pressure is only 6–8% of that required to achieve similar effects in single crystals using diamond anvil cells, revealing unexpectedly strong tunability in the thin-film form. Additionally, signs of spin-density wave (SDW) order are observed in films on YAlO₃ substrates but suppressed on LaAlO₃ substrates. Hall effect measurements indicate a multiband electronic structure. These results demonstrate that La₃Ni₂O₇ thin films can approach a strongly fluctuating ordered state under moderate pressures, offering a new pathway for studying the origin of non-Fermi liquid behavior and high-pressure superconductivity in thin-film systems.

Materials

• La₃Ni₂O₇
• SrLaAlO₄ (001)

Methods

• epitaxial growth
• transport measurements
• hydrostatic pressure

Keywords

• non fermi liquid behavior
• fermi liquid
• kondo effect
• hydrostatic pressure
• tunability

Highlights

• Strong tunability of La₃Ni₂O₇ in thin film form and proximity to a strongly fluctuating ordered state leading to non-Fermi liquid behavior under modest applied pressures.

Conclusions

• La₃Ni₂O₇ thin films on LAO(001) exhibit Fermi liquid-like metallic behavior with a slight Kondo-like upturn at low temperatures, evolving toward non-Fermi liquid behavior (T₁.4) at 1.41 GPa.
• The ability to tune the normal state to non-Fermi liquid behavior under modest hydrostatic pressure (only 6-8% of DAC pressure in single crystals) is noteworthy.

Main claims

• Fermi liquid to non-Fermi liquid transition in La₃Ni₂O₇ thin films under hydrostatic pressure
  • Evidence: Transport measurements show that the La₃Ni₂O₇ thin films on LAO(001) exhibit Fermi liquid-like metallic behavior with a slight Kondo-like upturn at low temperatures, which evolves with the application of modest hydrostatic pressures toward non-Fermi liquid behavior with a temperature dependence of resistance approaching ≈ T₁.4 at 1.41 GPa.
• Non-Fermi liquid behavior achieved at only 6-8% of the pressure required in single crystals
  • Evidence: The ability to tune the normal state resistivity of La₃Ni₂O₇ films to display non-Fermi liquid behavior under such a modest hydrostatic pressure range – only 6 - 8 % of that typically applied via diamond anvil cell (DAC) in La₃Ni₂O₇ single crystals to achieve comparable effects – is both noteworthy and unexpected.
• Evidence of spin-density wave ordering in films on YAlO₃ substrates
  • Evidence: Figure 3a displays the sheet resistance Rx_y as a function of temperature for the film on YAO(110)… Both the derivative and the raw resistance-temperature data exhibit a pronounced kink near 120 K, suggesting a transition at this temperature.,Similar transitions have been reported for nickelate thin films and single crystals, and were attributed to the spin density wave (SDW) ordering mechanisms.
• Multiband electronic structure in La₃Ni₂O₇ films
  • Evidence: the calculated Hall coefficient RH is positive at measured temperatures and decreases with increasing temperature. Such behavior may indicate multiband electronic structure of the LNO₃₂₇ films

Workflow

• sample_preparation — Successfully grew epitaxial bilayer La₃Ni₂O₇ thin films with controlled strain and oxygen content
  • Materials: La₃Ni₂O₇ polycrystalline targets; LaAlO₃ (001) substrates; SrLaAlO₄ (001) substrates; YAlO₃ (110) substrates; SrTiO₃ capping layer targets; high-pressure oxygen (15 bar)
  • Methods: Pulsed laser deposition (KrF excimer laser 248 nm); ex-situ annealing in high-pressure furnace
  • Observations: Epitaxial growth confirmed by RHEED and XRD; Films fully strained on substrates with lattice mismatches -1.1% (LAO) and -2% (SLAO); Only films grown at ≈100 mtorr O₂ show pure bilayer La₃Ni₂O₇ phase
• transport_measurement — Transport properties show strain-dependent behavior and evolve with pressure
  • Materials: La₃Ni₂O₇ thin films on LAO, SLAO, YAO substrates
  • Methods: Four-probe resistivity measurement; Hall effect measurement using Van der Pauw configuration; Piston-cylinder cell (PCC) for hydrostatic pressure; Physical Property Measurement System (PPMS)
  • Observations: On LAO: metallic behavior with Kondo-like upturn at low T at ambient; On YAO: kink near 120 K indicating SDW transition; Hall coefficient positive, decreasing with T; Under pressure: Kondo upturn suppressed, resistance increases slightly at low T
• data_analysis — Resistance exponent changes from 2 to 1.4 with pressure, indicating transition from Fermi liquid to non-Fermi liquid behavior
  • Methods: Power-law fitting: R(T) = R₀ + AT^α; Kondo model fitting: R ≈ -ln(T) + T₂
  • Observations: At ambient: best fit with Kondo model; At₀.53 GPa: α = 2 (Fermi liquid); At₁.41 GPa: α = 1.4 (non-Fermi liquid)
• interpretation — La₃Ni₂O₇ thin films are tuned close to a quantum critical point under modest pressure, providing a new platform for studying non-Fermi liquid behavior and high-pressure superconductivity
  • Methods: Comparison with theoretical predictions for quantum criticality; Comparison with single crystal studies
  • Observations: Non-Fermi liquid behavior consistent with spin fluctuation scattering; Pressure required (1.41 GPa) is only 6-8% of that in single crystals; Suggests proximity to SDW quantum critical point