Density-wave phases, anisotropic transport, and Planckian dissipation in single crystals of the superconductor La₃Ni₂O₇

摘要

研究人员利用高质量La₃Ni₂O₇单晶，通过精确测量面内和面外电阻率，建立了高精度的压力–温度相图。他们分辨出两个具有不同压力依赖性的密度波相关异常：其中低温异常T₁先被压制，在约10 GPa结构相变后急剧增强，而高温自旋密度波异常T₂则单调升高。压力诱导的结构转变不仅增大了两方向电阻率，还显著增强了低温电阻率各向异性，表明密度波序对电荷动力学有深刻影响。一旦压力将密度波相完全压制，在相边界处出现零电阻超导，其起始温度达68 K，正常态电阻率在超导转变温度以上至300 K的宽温区内呈线性温度关系，散射率落入普朗克极限范围。这些结果说明压力通过调控密度波序，重构了各向异性电荷输运，进而产生强散射的奇异金属态和超导电性，确立了密度波关联和普朗克耗散是La₃Ni₂O₇的显著特征。

材料

• La₃Ni₂O₇

方法

• high-pressure resistivity measurements
• Montgomery method for anisotropic transport
• synchrotron X-ray diffraction
• transmission electron microscopy
• scanning electron microscopy
• energy-dispersive X-ray spectroscopy
• Laue diffraction
• single crystal X-ray diffraction
• structural refinement

关键词

• density wave order
• spin density wave
• charge order
• planckian dissipation
• strange metal
• temperature linear resistivity
• resistivity anisotropy
• pressure induced structural transition
• superconductivity
• quantum critical fluctuations

亮点

• High-quality, oxygen-stoichiometric, stacking-fault-free La₃Ni₂O₇ single crystals are synthesized for the first time.
• The low-temperature density-wave anomalyT₁ does not vanish below 10 GPa but is abruptly enhanced across the structural transition.
• The transport anisotropy increases dramatically at low temperatures upon entering the tetragonal phase, driven by the density‑wave order.
• The normal‑state T‑linear resistivity slope and Fermi velocity place La₃Ni₂O₇ in the Planckian dissipation regime, similar to other strange metals.
• The pressure–temperature phase diagram is highly reproducible across several single crystals, confirming the intrinsic nature of the electronic modifications.

结论

• Two distinct density-wave anomalies, T₁ and T₂, are resolved: T₁ is initially suppressed and then sharply enhanced after the structural transition, while T₂ (spin-density-wave) increases monotonically with pressure.
• The orthorhombic-to-tetragonal structural transition enhances both in-plane and out-of-plane resistivities and strongly increases low-temperature resistivity anisotropy due to the density-wave order.
• Superconductivity with zero resistance emerges near the boundary where the density-wave phases are fully suppressed, with an onset T_c up to 68 K.
• Above T_c, the normal-state resistivity displays a T‑linear dependence over a wide temperature range, and the extracted scattering rate lies within the Planckian limit, revealing a strange‑metal state.
• Robust density-wave correlations and Planckian dissipation are defining features of La₃Ni₂O₇, and superconductivity develops from this strongly correlated normal state.

主要论断

• Two distinct density-wave-related anomalies (T₁ and T₂) exhibit contrasting pressure dependences, with T₁ enhanced after a structural transition.
  • 证据: Temperature derivative of in-plane resistivity shows T₁ and T₂ anomalies,Phase diagram Fig. 2e shows T₁ initially suppressed then sharply increased near 10 GPa, T₂ monotonically increasing
• The pressure-induced structural transition enhances low-temperature resistivity and its anisotropy.
  • 证据: At ≈8-10 GPa, ρab and ρc increase at low T, and ρc/ρab rises sharply below 150 K (Figs. 3,4a),The change coincides with orthorhombic-to-tetragonal transition
• Zero-resistance superconductivity emerges near the boundary where density-wave phases are fully suppressed.
  • 证据: T_c onset and T_c zero appear at pressures >14 GPa where T₁, T₂ and resistivity upturn disappear (Fig. 2e),T_c onset up to 68 K, zero resistance up to 55 K at 20 GPa
• The normal-state resistivity above T_c exhibits T-linear dependence and Planckian dissipation.
  • 证据: ρab is T-linear from ≈80 K to 300 K at 18 and 20 GPa with small residual resistivity (Fig. 4f),Scattering rate α ≈ 1.6 ± 0.4, close to Planckian limit (Fig. 4c)

研究流程

• sample_preparation — High-quality oxygen-stoichiometric bilayer La₃Ni₂O₇ single crystals were obtained.
  • 材料: La₂O₃ (99.99%); NiO (99.99%); flux; oxygen agent
  • 方法: high-pressure growth in cubic-anvil press at 3 GPa; heating at 1373 K then slow cooling to 1073K; X-ray diffraction; Laue diffraction; STEM and EDS mapping
  • 观察: large single crystals up to 220 μm; orthorhombic Am₂m structure; no oxygen vacancies; no stacking faults; homogeneous element distribution
• measurement — Pressure-dependent resistivity and anisotropy reveal density-wave anomalies and superconductivity.
  • 材料: single crystal samples 2#-a, 2#-d, 2#-e; silver epoxy or nanoparticle silver paste electrodes; Daphne 7575/7676 pressure transmitting medium; cubic-anvil press; PPMS
  • 方法: four-contact resistivity measurements; Montgomery method for anisotropy; in-plane (ab) and out-of-plane (c) resistivity under pressure
  • 观察: ρab decreases with P at 300 K, then develops semiconducting upturn at intermediate P; two anomalies T₁ and T₂ in resistivity derivative; resistivity anisotropy ρc/ρab increases sharply at low T near 10 GPa; superconducting transition with T_c onset up to 68 K and zero resistance up to 55 K at 20 GPa
• analysis — Density-wave orders are modified by pressure, and the normal state at high pressure exhibits Planckian dissipation.
  • 方法: temperature derivative of resistivity to identify characteristic temperatures; Drude model to extract scattering rate; comparison with Planckian limit α = (ħ/τ)/(k_B T); construction of P-T phase diagram
  • 观察: T₁ initially suppressed then sharply increased around 10 GPa (structural transition); T₂ increases monotonically with pressure; T-linear ρab from ≈80 K to 300 K at 18-20 GPa with slope ≈0.28 μΩ cm/K; scattering rate α ≈ 1.6 ± 0.4, close to Planckian limit
• interpretation — Superconductivity in La₃Ni₂O₇ develops from a strongly correlated state with Planckian dissipation when robust density-wave orders are fully suppressed.
  • 观察: superconductivity emerges only after full suppression of T₁, T₂, and resistivity upturn; strange-metal state with T-linear resistivity and strong scattering