Frustrated magnetic interactions in FeSe

The structurally simplest high-temperature superconductor FeSe exhibits an intriguing superconducting nematic paramagnetic phase with unusual spin excitation spectra that are different from typical waves; thus, determining its effective magnetic exchange interactions is challenging. Here we report neutron scattering measurements of fluctuations in the tetragonal phase. We show equal-time structure factor, $\mathcal{S}(\mathbf{Q})$, can be effectively modeled using self-consistent Gaussian approximation calculation highly frustrated nearest-neighbor (${J}_{1}$) and next-nearest-neighbor (${J}_{2}$) couplings, very weak further neighbor interaction. Our results elucidate magnetism FeSe, which provides a natural explanation for tunable superconductivity nematicity related materials.