摘要
该研究开发了一种兆帕级高压氧辅助化学合成路线，成功实现了向较重稀土元素延伸的无限层镍酸盐（(RE1-yRE'y)1-xEuxNiO2，RE/RE'：Pr、Nd、Sm、Gd、Dy）的有效生长。通过Eu2+/Eu3+变价实现空穴掺杂，在Nd1-xEuxNiO2和Pr1-xEuxNiO2体系的超导圆顶边界处，观察到源于Eu2+ 4f7磁矩与磁涨落竞争而产生的稳健单轴各向异性磁场重入超导，而在最佳掺杂区则表现为常规高温超导，临界电流密度高达~266 kA/cm2（2 K），超越传统Sr/Ca掺杂体系。进一步引入不同RE'磁性离子可调节交换场强度，从而调制量子临界性：既增强重入行为，也可将Tc提升至40.1 K。该工作揭示了稀土4f磁矩在调制配对强度与量子临界性中的关键作用，为利用无限层镍酸盐平台研究4f相关的非常规超导与量子相变奠定了合成基础。
材料
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方法
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关键词
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亮点
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结论
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主要论断
- A chemical avenue enables effective growth of (RE,RE')1-xEuxNiO2, revealing RE-4f-related quantum competition between high-Tc and reentrant superconductivity.
- 证据: 'Herein, we open up chemical avenues to enable effective growth of (RE1-yRE'y)1-xEuxNiO2 (RE/RE': Pr, Nd, Sm, Gd, Dy), giving rise to discoveries of RE-4f-related quantum competition between high-Tc and reentrant superconductivity.' (Abstract)
- Robust magnetic-field-reentrant superconductivity with uniaxial anisotropy is observed at superconducting-dome boundaries, stemming from Eu2+-4f7 competition between magnetic-fluctuation promoted pairing and exchange-field interactions.
- 证据: 'Robust magnetic-field-reentrant superconductivity with uniaxial anisotropy is observed at superconducting-dome boundaries, stemming from Eu2+-4f7 associated competition between magnetic-fluctuation promoted pairing and exchange-field interactions.' (Abstract)
- Quantum-criticality is further modulable via RE(RE')-magnetism, which either reinforces reentrancy or elevates Tc (40.1 K) with more robust critical-current-density (≈266 kA/cm2 at 2 K) beyond Sr-/Ca-doped counterparts.
- 证据: 'Their quantum-criticality is further modulable via RE(RE')-magnetism, which either reinforces reentrancy or elevates Tc (40.1 K) with more robust critical-current-density (≈266 kA/cm2 at 2 K) beyond Sr-/Ca-doped counterparts.' (Abstract)
- Combining magneto-transport and LE-μSR unveils that strengthened Cooper pairing and promoted magnetic fluctuation via optimum Eu2+-4f7 interactions are responsible for elevated Tc and Jc beyond Sr/Ca systems.
- 证据: 'Further introduction of different RE′ magnetic ions allowed tuning of the exchange field strength and thereby modulation of quantum criticality, both enhancing the reentrant behavior and elevating T_c to 40.1 K.' (Summary),'combining magneto-transport and LE-μSR measurements unveils the concomitant occurrence of strengthened Cooper pairing and promoted magnetic fluctuation' (Conclusion paraphrase)
研究流程
- Synthesis of infinite-layer nickelate thin films via high-pressure oxygen-assisted chemical route — Effective growth of (RE,RE')1-xEuxNiO2 infinite-layer nickelates with heavier rare-earths enabled by MPa-high-pO2 synthesis, overcoming thermodynamic limitations of vacuum epitaxy.
- 材料: RE(NO3)3; Ni(CH3COO)2; ethylene glycol monomethyl ether (EGME); NdGaO3 (110) substrate; CaH2
- 方法: spin coating; MPa-range high-pressure oxygen annealing; topotactic reduction with CaH2
- 观察: Perovskite precursor films exhibit metal-insulator transitions (T_MIT increasing with Eu content); XRD confirms transformation to infinite-layer structure after reduction; Cross-section STEM shows ≈20 nm thick films with coherent interfaces; some reduced crystallinity
- Transport measurements and superconducting phase diagram mapping — Robust magnetic-field-reentrant superconductivity with uniaxial anisotropy emerges at quantum boundaries of the superconducting dome, competing with high-Tc superconductivity, associated with Eu2+ 4f7 magnetic moments.
- 材料: Nd1-xEuxNiO2 films; Pr1-xEuxNiO2 films
- 方法: resistivity vs temperature under magnetic fields up to 35T; magnetic field-dependent resistivity mapping; critical current density measurements
- 观察: Optimum-doped Nd0.55Eu0.45NiO2 shows conventional superconductivity with Tc,onset ≈37.6 K, monotonically suppressed by field; Underdoped (x=0.2-0.3) and overdoped (x=0.52-0.6) samples exhibit field-reentrant superconductivity, zero resistance re-emerging at high fields; Phase diagrams reveal reentrance exclusively at superconducting dome boundaries; Jc reaches 266 kA/cm2 at 2 K for optimum doping, robust under 9 T field
- Modulation of reentrant behavior and Tc via rare-earth substitution — Quantum criticality between reentrant and high-Tc SC is tunable via RE' magnetism; Gd3+ (4f7) reinforces reentrancy via Jaccarino-Peter effect, while weak magnetic RE' mixing elevates Tc by disturbing spin ordering.
- 材料: (Nd1-yRE'y)0.65Eu0.35NiO2 with RE' = Pr, Sm, Gd, Dy
- 方法: same synthesis route; resistivity under magnetic field; angular-dependent magnetotransport
- 观察: Gd-substituted samples (y=0.05,0.1,0.2) show enhanced field-reentrant superconductivity; Dy, Pr, Sm show conventional SC; Angular mapping reveals uniaxial anisotropy with reentrant region near c-axis; Introducing RE' with reduced magnetism (Pr, Sm, mixed) elevates Tc up to 40.1K
- Muon spin spectroscopy and pairing mechanism investigation — Enhanced magnetic fluctuations and spin ordering at superconducting state in Eu-doped nickelates strengthen Cooper pairing, explaining elevated Tc and Jc beyond Sr/Ca-doped systems.
- 材料: Nd0.6Eu0.4NiO2 film on LSAT (100) substrate
- 方法: low-energy muon-spin spectroscopy (LE-μSR)
- 观察: Abrupt increase in ZF relaxation rate λ_ZF below Tc, to ≈2.5 μs-1, much larger than Sr-doped counterparts (0.22-0.48 μs-1); Stretch exponent β decreases to ≈0.5-0.6, indicating spin-glass-like state below Tc