来源 自动抓取
作者 Anna Eyal, Gad Koren
arXiv / 出版方 https://arxiv.org/abs/2502.17892
PDF https://arxiv.org/pdf/2502.17892
相关度评分 5.055
主分类 cond-mat.supr-con
发布日期 2026-06-23
研究范式 实验研究
样品形态 薄膜

摘要

本研究在高度还原且导电的SrTiO3衬底上制备了缺氧镍酸盐薄膜，通过迈斯纳效应和输运测量观察到超导起始温度达到50–70 K，并在20–25 K实现零电阻，表明超导存在于薄膜中的岛状区域。在约48 K处出现巨大的顺磁迈斯纳效应峰，进一步支持了该温度附近的超导转变。此外，还观测到非互易、无磁滞的超导二极管效应，其极性可完全偏振并反转。薄膜由多种Ruddlesden-Popper相（包括无限层相）混合构成。这些增强的超导特性归因于缺氧薄膜与高度还原的SrTiO3衬底的协同作用。

材料

方法

关键词

亮点

  • The observed Tc onset of 50-70 K is the highest reported in reduced nickelate films at ambient pressure.
  • The fully polarized superconducting diode effect could be developed into a desirable device.
  • The highly reduced black STO substrate is essential for these observations and could be used as a substrate for other films needing permanent reduction.

结论

  • We observed a Tc onset enhancement to 50-70 K at ambient pressure in oxygen-deficient nickelate thin films on highly reduced black SrTiO3 substrates.
  • We observed a giant paramagnetic Meissner effect peak at about 48 K, supporting a superconducting transition just above it.
  • We observed a highly asymmetric, nonreciprocal, and non-hysteretic superconductive diode effect that could be fully polarized and polarity reversed.
  • The phase responsible for these effects in our multiphase films could not be singled out; one possibility is an electron-doped 327 phase.

主要论断

  • Superconducting transition onset is enhanced to 50–70 K at ambient pressure in oxygen-deficient nickelate films on highly reduced SrTiO3 substrates.
    • 证据: Meissner effect measurements showing diamagnetic onset at ≈50 K (Figs. 2b, 5a),Resistance drop starting at ≈70 K and zero resistance at 20–25 K (Figs. 3, 6),Abstract: 'Tc onset of 50-70 K was found in Meissner and transport measurements'
  • A giant paramagnetic Meissner effect (PME) peak is observed at ≈48 K under high magnetic fields (2000–4000 Oe).
    • 证据: SQUID measurements showing a positive magnetization peak just below 50 K (Fig. 5c),PME peak magnitude scales as H^(3/2) (Fig. 5d),Abstract: 'a giant paramagnetic-Meissner effect peak at about 48 K'
  • A non-reciprocal, non-hysteretic superconducting diode effect with full polarity reversibility is observed without external magnetic field.
    • 证据: Asymmetric voltage-current curves: Ohmic in one bias direction, supercurrent in the opposite (Fig. 7),Polarity reversal upon changing contact geometry (Fig. 8a,b),Abstract: 'asymmetric or nonreciprocal and non-hysteretic superconductive diode effect was observed'

研究流程

  • Sample Preparation — Reduction under vacuum produces highly reduced black STO substrates and oxygen-deficient nickelate films with multiple RP phases.
    • 材料: Nd0.8Sr0.2NiO3 (NSNO) ceramic target; Ti-terminated (100) SrTiO3 (STO) wafers; CaH2 powder for reduction
    • 方法: Pulsed laser deposition (PLD) using fourth-harmonic Nd-YAG laser (266 nm); Reduction annealing in Al packets with CaH2 at 450-500 °C under vacuum pumping
    • 观察: Virgin films: epitaxial (113) RP perovskite phase; Reduced films: mixed Ruddlesden-Popper phases (n=1,2,3,4,∞), polycrystalline; STO substrates become black and highly conductive (metallic); Ti diffusion from STO into film detected by EDS
  • Structural and Compositional Characterization — Films are inhomogeneous with multiple RP phases; Ti diffusion from substrate occurs; dominant phase varies with reduction time.
    • 材料: As-prepared and reduced films
    • 方法: X-ray diffraction (XRD) θ–2θ scans; Atomic force microscopy (AFM); High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM); Energy-dispersive X-ray spectroscopy (EDS)
    • 观察: XRD: (002) perovskite peak disappears after reduction; broad infinite-layer peak appears; polycrystalline rings in longer reductions; STEM: columnar defects, vertical disorder, identification of RP phases (327, 214, 4310, etc.); EDS: Ni aggregation into puddles, Ti substitution for Ni, stoichimetry preserved (Nd+Sr)/(Ni+Ti) ≈ 1; Aging effects: films lose superconductivity and STO loses blackness over months
  • Magnetic Characterization — Detection of superconductivity with onset Tc50–70 K and a giant PME peak supporting a superconducting transition near 50 K.
    • 材料: Reduced films on black STO substrates
    • 方法: SQUID magnetometry (MPMS3); Meissner effect protocol: zero-field cooling (ZFC) then field warming (FW); Paramagnetic Meissner effect (PME) measurements
    • 观察: Meissner diamagnetic signal onset at ≈50 K (films reduced 1 h and 6 h); Low-temperature Meissner transition at ≈7 K in 1 h reduced film; Giant paramagnetic Meissner effect (PME) peak at ≈48 K under fields of 2000–4000Oe; Net PME peak magnitude follows H^(3/2) power law
  • Transport Characterization — Observation of a field-free superconducting diode effect with fully polarizable and reversible polarity, and supercurrents consistent with weak-link behavior.
    • 材料: Same films
    • 方法: Four-probe resistance vs temperature (PPMS Dynacool); Voltage-current (V-I) characteristics (Keithley 2450 sourcemeter); Supercurrent extraction from V-I curves
    • 观察: Resistance drop starting at ≈70 K, zero resistance at 20–25K; Highly asymmetric V-I curves: diode effect (non-reciprocal, non-hysteretic); Polarity of diode effect reversible by changing contact geometry; Supercurrents decrease with temperature, vanish at ≈50K
  • Data Analysis and Interpretation — The highly reduced black STO substrate is essential for the observed Tc enhancement and novel effects; the mixed RP phases contribute to the inhomogeneous superconductivity.
    • 材料: Raw data from magnetic and transport measurements
    • 方法: Subtraction of STO substrate background (magnetic and resistance); Extraction of Tc onset and zero-resistance temperature; Comparison with literature on nickelates and reduced STO
    • 观察: Tc onset 50–70 K and zero resistance 20–25 K in both 1 h and 6 h reduced films; Diode effect and PME attributed to inhomogeneous film structure and highly reduced STO; Possible role of electron-doped 327 phase or interface effects