Time-reversal symmetry breaking superconductivity with electronic glass in nickelate (La, Pr, Sm)₃Ni₂O₇ films

摘要

研究团队通过对(La, Pr, Sm)₃Ni₂O₇双层镍酸盐薄膜进行电输运测量，发现了伴随电子玻璃行为的时间反演对称性破缺超导电性。该超导态出现在接近零电阻态的低温区域，表现出三个显著特征：一是非常规的磁电阻回滞，这是时间反演对称性破缺的直接证据，且在不同磁场方向下均保持稳健，与涡旋钉扎或长程磁有序有本质区别；连续氧还原同时削弱了超导电性和磁滞，揭示了它们与特定镍3d电子轨道的关联。二是电流-电压响应在零场下表现出磁历史依赖性和非互易性，进一步证实了自发的内禀时间反演对称性破缺。三是移除磁场后电阻呈现对数缓慢弛豫，这是玻璃态动力学的标志。这些现象首次在镍基超导体中揭示了兼具自发时间反演对称性破缺和内在玻璃态特性的超导态，为理解高温超导机理提供了重要的现象学和概念性突破。

材料

• (La、Pr、Sm)₃Ni₂O₇
• La₁.95Pr₁.05Ni₂O₇
• La₂.85Pr₀.15Ni₂O₇
• La₂.46Pr₀.24Sm₀.3Ni₂O₇

方法

• electrical transport measurements
• magnetoresistance
• current-voltage (I-V) characteristics
• Hall effect
• Berezinskii-Kosterlitz-Thouless (BKT) analysis
• time-dependent resistance relaxations
• oxygen content modulation

关键词

• time reversal symmetry breaking
• electronic glass
• superconducting glass state
• magnetoresistance hysteresis
• non reciprocal transport
• logarithmic resistance relaxation
• spin glass
• orbital selectivity

亮点

• The unconventional magnetoresistance hysteresis is robust under different magnetic field orientations and differs fundamentally from trapped vortices or long-range-ordered magnetism.
• Successive oxygen reductions simultaneously weaken both the superconductivity and hysteresis, revealing their mutual connections to selective electronic orbitals.
• The non-reciprocal current-voltage response is magnetic field history-dependent, exhibiting highly effective field-tunability and memory effect.
• Logarithmically slow resistance relaxations upon removal of magnetic field are hallmarks of glassy dynamics.

结论

• Through electrical transport study, we report the discovery of time-reversal symmetry breaking superconductivity with electronic glass in bilayer nickelate (La,Pr,Sm)₃Ni₂O₇ films.
• It emerges in the lower-temperature regime of superconducting transition to the zero-resistance state, and is captured by three remarkable characteristics: unconventional magnetoresistance hysteresis, magnetic field history-dependence and zero-field non-reciprocity in current-voltage responses, and logarithmically slow resistance relaxations.
• Our findings uncover an unprecedented superconducting state in the nickelate superconductors, providing phenomenological and conceptual advances for future research on high-T_c superconductivity.

主要论断

• Unconventional magnetoresistance hysteresis provides direct evidence of time-reversal symmetry breaking, distinct from trapped vortices or long-range magnetism.
  • 证据: abstract: 'Unconventional magnetoresistance hysteresis, the direct evidence of TRS breaking',full_text: hysteresis observed under both out-of-plane and in-plane fields, with coalescing minima at zero field
• Magnetic field history-dependence and zero-field non-reciprocity in I-V responses substantiate intrinsic and spontaneous TRS breaking.
  • 证据: abstract: 'Magnetic field history-dependence and zero-field non-reciprocity',full_text Fig. 3a-f show clear deviation between V(I+) and |V(I-)| at zero field
• Logarithmically slow resistance relaxations after field removal are hallmarks of glassy dynamics.
  • 证据: abstract: 'Logarithmically slow resistance relaxations upon the removal of magnetic field, the hallmarks of glassy dynamics',full_text Fig. 5b-g show R_S(τ) ∝ -β log₁₀ τ below 28K
• Successive oxygen reductions simultaneously weaken both superconductivity and hysteresis, revealing connection to selective electronic orbitals (likelyNi 3dx²-y²).
  • 证据: abstract: 'Successive oxygen reductions simultaneously weaken both the superconductivity and hysteresis',full_text Fig. 4a-d show systematic suppression with decreasing oxygen content

研究流程

• film_synthesis — High-quality single-crystalline films prepared.
  • 材料: (La,Pr,Sm)₃Ni₂O₇ thin films with various compositions
  • 方法: gigantic-oxidative atomic-layer-by-layer epitaxy (GAE); on SrLaAlO₄ (001) substrates
  • 观察: RHEED oscillations confirm layer-by-layer growth; XRD confirms pure phase
• transport_measurements — Three key signatures of TRS breaking glass superconductivity observed.
  • 材料: three compositions: La₁.95Pr₁.05Ni₂O₇, La₂.85Pr₀.15Ni₂O₇, La₂.46Pr₀.24Sm₀.3Ni₂O₇
  • 方法: four-electrode transport; magnetoresistance; Hall effect; current-voltage (I-V) characteristics
  • 观察: BKT transition, T_c^onset ≈48 K, T_c^zero ≈17K; hysteretic magnetoresistance below 26K; non-reciprocal I-V; logarithmic resistance relaxation