中国科技大学陈仙辉教授、吴涛教授团队揭示了双层镍酸盐La₃Ni₂O_7-δ的压力增强自旋密度波转变。这一研究成果于2025年2月17日发表在《科学通报》杂志上。

最近，有报道称a₃Ni₂O_7-δ在压力下具有液氮温度（77 K）以上的高温超导特征。这一发现立即激发了人们对双层镍酸盐中高温超导可能机制的浓厚兴趣。值得注意的是，从输运测量中推断出的压力依赖相图表明，高压下的超导性是由环境压力下密度波序的抑制引起的，这与高温超导体相似。因此，阐明密度波型转变的确切性质对于确定双层镍酸盐中的超导机制非常重要。

研究组对¹³⁹La核进行了核磁共振（NMR）光谱分析，以研究a₃Ni₂O_7-δ单晶中的密度波型转变。在高温下，两组清晰的¹³⁹La NMR峰与宽背景信号清晰可辨，这些信号归因于具有不同氧空位δ的两个双层Ruddlesden-Popper相的La（1）位点。随着温度的降低，La（1）位点的温度依赖性¹³⁹La NMR光谱和核自旋晶格弛豫率（1/T₁）提供了在转变温度（TSDW）以下（约150 K）自旋密度波（SDW）有序的证据。NMR光谱中的各向异性分裂表明，可能形成了磁矩沿c轴排列的双自旋条纹。

此外，研究组分析了高达2.7 GPa的压力依赖性SDW转变。令人惊讶的是，从La（1）位点的NMR测量中推断出的TSDW随着压力的增加而增加，这与之前在压力下的输运测量结果相反，并表明超导性和SDW之间存在一个神秘相图。相比之下，目前的¹³⁹La NMR对Ni-O平面中可能的电荷密度波（CDW）序不敏感。所有这些结果将有助于在双层镍酸盐中，建立超导性和磁相互作用之间的联系。

附：英文原文

Title: Pressure-enhanced spin-density-wave transition in double-layer nickelate La3Ni2O7δ

Author: Meng Wang b, Tao Wu a c d e, Xianhui Chen a c d e

Issue&Volume: 2025/02/17

Abstract: Recently, a signature of high-temperature superconductivity above the liquid nitrogen temperature (77 K) was reported for La3Ni2O7δ under pressure. This finding immediately stimulated intense interest in the possible mechanism of high-Tc superconductivity in double-layer nickelates. Notably, the pressure-dependent phase diagram inferred from transport measurements indicates that the superconductivity under high pressure emerges from the suppression of density-wave-like order at ambient pressure, which is similar to high-temperature superconductors. Therefore, clarifying the exact nature of the density-wave-like transition is important for determining the superconducting mechanism in double-layer nickelates. Here, nuclear magnetic resonance (NMR) spectroscopy of 139La nuclei was performed to study the density-wave-like transition in a single crystal of La3Ni2O7δ. At high temperatures, two sets of sharp 139La NMR peaks are clearly distinguishable from a broad background signals, which are ascribed to La(1) sites from two bilayer Ruddlesden-Popper phases with different oxygen vacancy δ. As the temperature decreases, the temperature-dependent 139La NMR spectra and nuclear spin-lattice relaxation rate (1/T1) for both La(1) sites provide evidence of spin-density-wave (SDW) ordering below the transition temperature (TSDW), which is approximately 150 K. The anisotropic splitting in the NMR spectra suggests the formation of a possible double spin stripe with magnetic moments aligned along the c-axis. Furthermore, we studied the pressure-dependent SDW transition up to ～ 2.7 GPa. Surprisingly, the TSDW inferred from NMR measurements of both La(1) sites increases with increasing pressure, which is opposite to the results from previous transport measurements under pressure and suggests an intriguing phase diagram between superconductivity and SDW. In contrast, the present 139La NMR is insensitive to the possible charge-density-wave (CDW) order in the Ni-O planes. All these results will be helpful for building a connection between superconductivity and magnetic interactions in double-layer nickelates.

DOI: 10.1016/j.scib.2025.02.019

Source: https://www.sciencedirect.com/science/article/abs/pii/S2095927325001811