Spin correlations in the nematic quantum disordered state of FeSe

The quantum-disordered magnetic ground state in FeSe, intertwined with superconductivity and nematicity has been a research focus in iron-based superconductors. However, the intrinsic spin excitations across the entire Brillouin zone in detwinned FeSe, crucial for understanding its magnetism and superconductivity, have remained unresolved. Using inelastic neutron scattering , we reveal that stripe spin excitations (Q=(1, 0)/(0, 1)) exhibit the C2 symmetry, while Néel spin excitations (Q=(1, 1)) retain C4 symmetry with in the nematic state. Temperature-dependent differences between Q=(1, 0) and (0, 1) spin excitations above the structural phase transition unambiguously reveals the nematic quantum disordered state. The similarity of the Néel excitations in FeSe and NaFeAs suggests that the Néel excitations are driven by enhanced 3dxy orbital correlations. By fitting the dispersion of stripe excitations using a Heisenberg Hamiltonian with J1-K-J2, we establish a spininteraction phase diagram, positioning FeSe near a crossover region between the antiferroquadrupolar, Néel, and stripe ordering.The results provide an experimental basis for microscopic theoretical of the intertwined orders in iron-based superconductors.

FeSe中与超导性和向列性交织的量子无序磁基态一直是铁基超导体的研究焦点。然而，解孪FeSe中整个布里渊区的本征自旋激发——这对理解其磁性和超导性至关重要——仍未得到解决。利用非弹性中子散射，我们发现条纹自旋激发（Q=(1,0)/(0,1)）表现出C2对称性，而奈尔自旋激发（Q=(1,1)）在向列态中保留C4对称性。结构相变以上Q=(1,0)和(0,1)自旋激发之间的温度依赖差异明确揭示了向列量子无序态。FeSe和NaFeAs中奈尔激发的相似性表明，奈尔激发由增强的3dxy轨道关联驱动。通过使用J1-K-J2的海森堡哈密顿量拟合条纹激发的色散，我们建立了自旋相互作用相图，将FeSe定位在反铁四极、奈尔和条纹有序之间的交叉区域附近。这些结果为铁基超导体中交织有序的微观理论提供了实验基础。