Complex electron interactions underlie the electronic structure of several families of quantum materials. In particular, the strong electron Coulomb repulsion is considered the key ingredient to describing the emergence of exotic and/or ordered phases of quantum matter, from high-temperature superconductivity to charge- and magnetic-order. However, a comprehensive understanding of fundamental electronic properties of quantum materials is often complicated by the appearance of an enigmatic partial suppression of low-energy electronic states, known as the pseudogap. Here we take advantage of ultrafast angle-resolved photoemission spectroscopy to unveil the temperature evolution of the low-energy density of states in the electron-doped cuprate Nd_2-xCe_xCuO₄, an emblematic system where the pseudogap intertwines with magnetic degrees of freedom. Using an optical excitation we drive the electronic system across the pseudogap onset temperature T*, and we report the direct relation between the momentum-resolved pseudogap spectral features and the spin-correlation length with a remarkable sensitivity. This transient approach, corroborated by mean-field model calculations, allows us to establish the pseudogap in electron-doped cuprates as a precursor to the incipient antiferromagnetic order even when long-range antiferromagnetic correlations are not established, as in the case of optimal doping.

复杂的电子相互作用是多种量子材料族的电子结构的基础。特别是，强电子库仑斥力被认为是描述从高温超导性到电荷序和磁序的量子物质异质相和/或有序相的出现的关键成分。但是，对量子材料基本电子性质的全面理解通常会由于低能电子态的神秘部分抑制的出现而变得复杂，这被称为伪间隙。在这里，我们利用超快角分辨光发射光谱技术揭示了电子掺杂铜酸盐Nd _2-x Ce _x CuO _4中低能量密度态的温度演化。这是一个象征性系统，其中伪间隙与磁性自由度交织在一起。使用光激发，我们使电子系统跨过伪间隙起始温度T *，并以显着的灵敏度报告了动量分辨出的伪间隙光谱特征与自旋相关长度之间的直接关系。这种瞬态方法得到了平均场模型计算的证实，即使在没有建立长距离反铁磁相关性的情况下（如最佳掺杂的情况），我们也可以在电子掺杂铜酸盐中建立伪间隙，作为初始反铁磁顺序的先驱。