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

Summary

B_y fabricating periodic nanohole arrays to construct infinite-layer nickelate superconducting thin films (Nd₀.₈Sr₀.₂NiO₂) into Josephson junction arrays, researchers systematically enhanced the phase fluctuations of the system. In the nanopatterned films, the weakening of macroscopic phase coherence drives the superconducting transition to exhibit a two-stage characteristic and ultimately tends toward an anomalous metallic ground state with saturated resistance. The emergence of charge-2e quantum oscillations indicates inter-array coherence, while the anomalous zero-field magnetoresistance peak marks the persistence of extreme quantum phase fluctuations down to very low temperatures. Notably, through the synergistic enhancement of nanopatterning and magnetic fields, a reversal of superconducting anisotropy is observed in Nd-nickelates, where the in-plane critical field becomes lower than the out-of-plane critical field. The evolution of this anisotropy may reveal an intrinsic exchange Zeeman field coupled to collective electronic states. These results elucidate how superconductivity evolves in response to phase fluctuations and establish nanopatterning as an effective paradigm for unveiling hidden intertwined orders in strongly correlated systems.

Materials

• Nd₀.8Sr₀.2NiO₂
• La₀.8Sr₀.2NiO₂

Methods

• PLD
• topotactic reduction
• RIE
• transport measurements

Keywords

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

Highlights

• 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.

Conclusions

• 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.

Main claims

• Nano-patterning enhances phase fluctuations, driving a two-stage superconducting transition and an anomalous metallic ground state with saturated resistance.
  • Evidence: 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.
  • Evidence: 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.
  • Evidence: 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.
  • Evidence: 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

Workflow

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