Emergent quantum phenomena via phase-coherence engineering in infinite-layer nickelate superconductors

摘要

通过制备周期性纳米孔阵列将无限层镍酸盐超导薄膜（Nd₀.8Sr₀.2NiO₂）构建为约瑟夫森结阵列，研究人员系统地增强了系统的相位涨落。在纳米图案化的薄膜中，宏观相位相干的减弱驱动了超导转变呈现两阶段特征，并最终趋向于电阻饱和的反常金属基态。电荷2e量子振荡的出现表明了阵列间的相干性，而零场磁电阻反常峰则标志着极端量子相位涨落持续至极低温度。值得注意的是，通过纳米图案化与磁场的协同增强，在Nd-镍酸盐中观测到超导各向异性反转，即面内临界场低于面外临界场，该各向异性的演化可能揭示了与集体电子态耦合的内禀交换塞曼场。这些结果阐明了超导如何响应相位涨落而演化，并确立了纳米图案化作为揭示强关联系统中隐藏交织序的有效范式。

材料

• Nd₀.8Sr₀.2NiO₂
• La₀.8Sr₀.2NiO₂

方法

• PLD
• topotactic reduction
• RIE
• transport measurements

关键词

• josephson junction arrays
• phase fluctuations
• anomalous metal
• superconducting anisotropy reversal

亮点

• First observation of superconducting anisotropy reversal in nano-patterned Nd-based nickelates.
• Establishes nano-patterning as a powerful method to uncover hidden intertwined orders in strongly correlated systems.
• Shows that the resistance saturation in the anomalous metal state synchronizes with the dephasing rate of Cooper pairs.

结论

• Nano-patterning enhances phase fluctuations, driving a two-stage superconducting transition towards an anomalous metallic ground state.
• h/2e quantum oscillations demonstrate inter-island coherence via Cooper pairs.
• A zero-field magnetoresistance peak indicates extreme quantum phase fluctuations at ultralow temperatures.
• In Nd-nickelates, nano-patterning and magnetic fields cause a reversal of superconducting anisotropy (in-plane Bc < out-of-plane Bc), revealing an internal exchange-Zeeman field.

主要论断

• Nano-patterning enhances phase fluctuations, driving a two-stage superconducting transition and an anomalous metallic ground state with saturated resistance.
  • 证据: abstract: 'weakening of macroscopic phase coherence drives a two-stage superconducting transition towards an anomalous metallic ground state',full_text Fig. 2b shows two-stage transition with T₁ and T₂
• Charge-2e quantum oscillations manifest coherence across the array; an anomalous zero-field magnetoresistance peak signals extreme quantum phase fluctuations.
  • 证据: abstract: 'emergence of charge-2e quantum oscillations' and 'anomalous zero-field magnetoresistance peak',full_text Fig. 3b,c show h/2e oscillations; Fig. 3f shows zero-field peak
• Anomalous reversal of superconducting anisotropy (in-plane critical field below out-of-plane) is observed, potentially unmasking an internal exchange-Zeeman field.
  • 证据: abstract: 'anomalous reversal of superconducting anisotropy',full_text Fig. 2c,d show Bc∥ < Bc⟂ below ≈4K
• The synchronization between resistance saturation and 1/L_Φ² associates the anomalous metallic state with dephasing of Cooper pairs.
  • 证据: full_text Fig. 3g shows R_S(T) overlaid with 1/L_Φ², highlighting synchronization,full_text discussion on duality between Cooper pairs and vortices

研究流程

• film_synthesis — High-quality infinite-layer nickelate films prepared.
  • 材料: Nd₀.8Sr₀.2NiO₂ thin films; La₀.8Sr₀.2NiO₂ thin films
  • 方法: pulsed laser deposition (PLD); topochemical reduction with CaH₂
  • 观察: Infinite-layer phase achieved
• nano_patterning — Periodic nano-holes effectively enhance phase fluctuations.
  • 材料: Nd₀.8Sr₀.2NiO₂ films with AAO mask
  • 方法: reactive ion etching (RIE); AAO membrane transfer
  • 观察: Josephson junction array (JJA) formed; two-stage superconducting transition observed
• transport_measurements — Phase coherence engineering reveals hidden quantum phenomena.
  • 材料: unpatterned and nano-patterned films
  • 方法: four-electrode transport; magnetoresistance; I-V characteristics; Hall effect
  • 观察: charge-2e quantum oscillations; zero-field magnetoresistance peak; anomalous anisotropy reversal; logarithmic resistance relaxation