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

摘要

该研究报道了在LaAlO₃(001)和SrLaAlO₄(001)基底上外延生长双层La₃Ni₂O₇薄膜的输运性质，并通过高压氧气退火和静水压进行调控。常压下，LaAlO₃基底上的薄膜表现出费米液体金属行为，伴随低温下的轻微Kondo-like上升；而施加0.53至1.41 GPa的静水压后，电阻温度依赖性逐渐演变为非费米液体行为，在1.41 GPa时趋近于~T¹⁴。值得注意的是，这一压力仅为单晶中通过金刚石对顶砧实现类似效应所需压力的6–8%，显示出薄膜形式下超乎预期的强可调性。此外，在YAlO₃基底上的薄膜中观察到自旋密度波（SDW）序的迹象，而在LaAlO₃基底上则被抑制。霍尔效应测量表明多带电子结构。这些结果揭示了La₃Ni₂O₇薄膜在适度压力下即可接近强涨落有序态，为非费米液体行为的起源和高压超导的薄膜化研究提供了新途径。

材料

• La₃Ni₂O₇
• SrLaAlO₄ (001)

方法

• epitaxial growth
• transport measurements
• hydrostatic pressure

关键词

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

亮点

• 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.

结论

• 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.

主要论断

• Fermi liquid to non-Fermi liquid transition in La₃Ni₂O₇ thin films under hydrostatic pressure
  • 证据: 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
  • 证据: 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
  • 证据: 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
  • 证据: 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

研究流程

• sample_preparation — Successfully grew epitaxial bilayer La₃Ni₂O₇ thin films with controlled strain and oxygen content
  • 材料: La₃Ni₂O₇ polycrystalline targets; LaAlO₃ (001) substrates; SrLaAlO₄ (001) substrates; YAlO₃ (110) substrates; SrTiO₃ capping layer targets; high-pressure oxygen (15 bar)
  • 方法: Pulsed laser deposition (KrF excimer laser 248 nm); ex-situ annealing in high-pressure furnace
  • 观察: 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
  • 材料: La₃Ni₂O₇ thin films on LAO, SLAO, YAO substrates
  • 方法: Four-probe resistivity measurement; Hall effect measurement using Van der Pauw configuration; Piston-cylinder cell (PCC) for hydrostatic pressure; Physical Property Measurement System (PPMS)
  • 观察: 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
  • 方法: Power-law fitting: R(T) = R₀ + AT^α; Kondo model fitting: R ≈ -ln(T) + T₂
  • 观察: 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
  • 方法: Comparison with theoretical predictions for quantum criticality; Comparison with single crystal studies
  • 观察: 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