Spin correlations in the nematic quantum disordered state of FeSe

Liu, R.*; Stone, M. B.*; Gao, S.*; Nakamura, Mitsutaka   ; Kamazawa, Kazuya*; Krajewska, A.*; Walker, H. C.*; Cheng, P.*; Yu, R.*; Si, Q.*; Dai, P.*; Lu, X.*

The quantum-disordered state in FeSe, intertwined with superconductivity and nematicity, has been a research focus in iron-based superconductors. Temperature-dependent differences between Q= (1, 0) and (0, 1) spin excitations above the structural transition unambiguously reveals the nematic quantum disordered state. Comparison with NaFeAs suggests the Neel excitations originate from enhanced 3dxy orbital correlations. Modeling the stripe dispersions using a J1-K-J2 Heisenberg Hamiltonian, we establish a spininteraction phase diagram, positioning FeSe near a crossover regime between the antiferroquadrupolar, Neel, and stripe orders. Our results provide key insights into themicroscopic spin interactions and their role in the intertwined orders in iron-based superconductors.