Controlling the Band Filling and the Band Width in Nickelate Superconductors

摘要

本研究采用高压合成与静水高压输运技术，系统调控双层镍酸盐La₃Ni₂O₇家族中的能带宽度和能带填充，以探究其对超导电性及非超导态性质的影响。通过将La部分替换为较小的Nd（增大NiO₆八面体倾斜、减小带宽），超导相所需压力显著升高；而同时引入Sr进行空穴掺杂则反转此趋势，使超导起始压力降低。在非超导态中，观察到多达三种特征电阻异常，其随压力演化，可能分别对应与超导相互竞争的电荷密度波和自旋密度波有序态。综合对比不同成分样品的相图，表明带宽和填充的独立控制是揭示该体系非常规超导机理及其竞争序的关键。

材料

• La₃Ni₂O₇
• La₂NdNi₂O₇
• La₁.9NdSr₀.1Ni₂O₇
• La₂.9Sr₀.1Ni₂O₇
• La₁.8NdSr₀.2Ni₂O₇

方法

• high-pressure synthesis
• transport measurements
• X-ray diffraction
• scanning electron microscopy with energy-dispersive X-ray (SEM-EDX)
• STEM
• electron energy loss spectroscopy (EELS)

关键词

• bandwidth
• band filling
• density wave anomalies
• phase diagram

亮点

• Independent control of bandwidth and filling is key to unraveling the mechanism of unconventional superconductivity and its competing orders.
• The anomalies exhibit opposite pressure dependences, in contrast to cuprates.

结论

• Partial substitution of La with Nd increases the pressure required for superconductivity, while co-introducing Sr lowers it.
• Up to three characteristic resistance anomalies are observed in the nonsuperconducting state, likely corresponding to CDW and SDW orders that compete with superconductivity.

主要论断

• Partial substitution of La with smaller Nd increases the pressure required to induce superconductivity in bilayer nickelates, while co-introducing Sr reverses this trend
  • 证据: Transport measurements under pressure show that La₂NdNi₂O₇ requires ≈20 GPa for superconductivity, compared to ≈10 GPa for La₃Ni₂O₇; La₁.9NdSr₀.1Ni₂O₇ has onset at ≈14 GPa

研究流程

• Sample synthesis — High-quality samples with controlled band width and filling
  • 材料: La_3-xNd_xNi₂O₇ and Sr-doped variants
  • 方法: High-pressure synthesis; KClO₄ as oxidizing agent
  • 观察: XRD, SEM-EDX, STEM-EELS
• High-pressure transport measurements — Nd substitution shifts superconductivity to higher pressure, while Sr doping lowers it
  • 材料: Cubic anvil press
  • 方法: Resistivity under pressure up to 20 GPa
  • 观察: Resistance anomalies at various temperatures; Superconducting onset and zero resistance