Counterintuitive inverse superconducting transition beyond 4He-cooling limit

摘要

本文报道了在Eu基无限层镍酸盐（Eu_xNd_1-xNiO₂和Eu_xPr_1-xNiO₂）中实现的超过液氦冷却极限的逆超导转变。通过磁场调控，在过掺杂和欠掺杂区域均观察到超导零电阻态被限制在较低临界温度（T_c-inv约2.6–5.4 K）与较高正常T_c之间，升温或增加电流密度可从电阻态驱动进入超导态，并在更高温度和电流下再次消失。系统变温输运测量表明，这一Kelvin区间的逆超导转变源于温度变化引起的Eu²⁺4f⁷相关补偿有效磁场与上临界场的交替主导，并得到了磁场下约300 mK处超导重现所形成的温度诱导重入超导现象的支持。该工作建立了磁相互作用重构的高温超导体系作为探索逆转热退相干范式的量子现象的平台，也为量子相变器件的反向设计开拓了应用场景。

材料

• Eu_xNd_1-xNiO₂
• Eu_xPr_1-xNiO₂

方法

• Electrical resistivity measurements
• Magnetic field-dependent transport
• Current-voltage (I-V) measurements
• High-field magneto-transport
• X-ray diffraction (XRD)
• X-ray photoelectron spectroscopy (XPS)
• STEM
• Ginzburg-Landau modeling
• Fischer model fitting
• Werthamer-Helfand-Hohenberg (WHH) theory

关键词

• inverse superconducting transition
• temperature induced reentrant superconductivity
• jaccarino peter compensation
• upper critical field
• thermal decoherence reversal

亮点

• First realization of inverse superconducting transitions above the liquid-helium cooling limit (T_c-inv ≈2.6–5.4 K) in Eu-based infinite-layer nickelate thin films.
• Superconductivity is confined between a lower inverse critical temperature and a higher conventional critical temperature, and can be activated by both temperature rise and increasing current density.
• Direct observation of temperature-induced reentrant superconductivity—superconductivity reappears upon cooling to ≈100–300 mK after vanishing at a lower temperature—unprecedented in known superconducting systems.
• The inverse transition emerges at both overdoped and underdoped boundaries, while optimum doping screens it, highlighting the role of magnetic Eu₂+ 4f7 moments and exchange-field compensation.
• The work establishes magnetic-interaction-reconfigured high-T_c superconductors as a platform for quantum phenomena that reverse the thermal decoherence paradigm.

结论

• Field-modulated inverse superconducting transitions above the 4He-cooling limit are identified in Eu_xRE_1-xNiO₂ thin films at both overdoped and underdoped phase boundaries of the superconducting dome.
• The inverse superconducting transitions are driven by a lower-threshold critical temperature T_c-inv to reach zero resistance, which is eliminated at the normal critical temperature T_c.
• Superconductivity can also be triggered by current density from a resistive state below T_c-inv, and further vanishes at a higher current threshold.
• The temperature-induced alternating dominance between the effective magnetic field and the upper critical field Hc₂ plausibly explains the inverse superconducting transition in the Kelvin range.
• Reemerged superconductivity below sub-Kelvin temperatures reveals an extended framework, giving rise to temperature-induced reentrant superconducting phenomenon.
• These collective findings establish magnetic ordering intertwined high-T_c systems as a fertile platform for exploring quantum phenomena that overcome thermal decoherence, redefining architectures for quantum-phase-transition devices.

主要论断

• Field-modulated inverse superconducting transitions are realized above the 4He-cooling limit in Eu-based infinite-layer nickelates.
  • 证据: ρ-T curves show zero resistance confined between T_c-inv and T_c under magnetic fields (Fig. 1a,b).,The inverse transition is reversible and path-independent (inset of Fig. 1b, Suppl. Fig. 5).
• Superconductivity can be triggered not only by cooling below T_c but also by heating above T_c-inv or by increasing current density.
  • 证据: Temperature-dependent resistivity shows superconducting state emerging upon warming through T_c-inv (Fig. 1b).,Current-voltage characteristics demonstrate a drop to zero voltage at a finite current threshold (Extended Data Fig. 3).
• The inverse transition is plausibly explained by temperature-driven alternating dominance of the effective magnetic field (Htot) relative to the upper critical field (Hc₂).
  • 证据: Plots of Htot(T) and Hc₂(T) intersect twice at fields 1–2 T, defining T_c-inv and T_c (Fig. 2b).,Fischer-type WHH fitting of high-field phase boundaries (Fig. 2a).
• A temperature-induced reentrant superconductivity appears below ≈100–300 mK under magnetic fields, extending beyond the Jaccarino-Peter compensation framework.
  • 证据: Low-temperature ρ-T measurements reveal re-emergence of superconductivity below T c' ≈100–300 mK (Fig. 4a).,The H-T phase diagram deviates from the J-P + mean-field prediction at low T (Fig. 4b).
• Magnetic-interaction-reconfigured high-T_c systems serve as fertile platforms for exploring quantum phenomena that reverse the thermal decoherence paradigm.
  • 证据: The observation of both inverse and reentrant superconductivity in a high-T_c system implies new design principles for quantum devices.,The negative pairing strength associated with the inverse transition (−0.19 T/K) hints at magnetically promoted pairing.

研究流程

• sample_synthesis — Epitaxial thin films of Eu-based infinite-layer nickelates were successfully grown on a special substrate.
  • 材料: Eu; Nd; Pr; perovskite precursor films; special substrate
  • 方法: thin film growth; soft chemical reduction
  • 观察: synthesized Eu_xNd_1-xNiO₂ and Eu_xPr_1-xNiO₂ thin films
• transport_measurement — Inverse superconducting transitions were observed above the liquid-helium cooling limit, driven by temperature, magnetic field, and current density.
  • 材料: synthesised thin films; cryostat; superconducting magnet
  • 方法: temperature-dependent resistivity (ρ-T); field-dependent resistivity (ρ-H); current-voltage (I-V) characteristics
  • 观察: inverse superconducting transition at T_c-inv ≈2.6–5.4 K with zero resistance between T_c-inv and T_c; field-reentrant superconductivity; current-driven transition from resistive to superconducting state; temperature-induced reentrant superconductivity below ≈100–300 mK
• phenomenological_analysis — The inverse superconducting transition is explained by a temperature-dependent crossover in dominance between effective magnetic field and upper critical field.
  • 材料: high-field magnetotransport data
  • 方法: Fischer-type modified Ginzburg-Landau fitting; Brillouin function for exchange field HJ(T); Werthamer-Helfand-Hohenberg (WHH) theory for Hc₂(T)
  • 观察: two intersection points between Htot(T) and Hc₂(T) at fields 1–2T; Hc₂ upturn at low temperatures
• phase_diagram_construction — Inverse superconducting transition emerges near the edges of the superconducting dome where magnetic interactions are enhanced.
  • 材料: transport data for multiple Eu compositions
  • 方法: construction of superconducting phase diagram in temperature-field-composition space
  • 观察: inverse superconducting transitions occur only at underdoped and overdoped boundaries; optimally doped samples show no inverse transition or field-reentrance