Wang, ZhentaoHu, Wen-JunNevidomskyy, Andriy H.2017-05-032017-05-032016Wang, Zhentao, Hu, Wen-Jun and Nevidomskyy, Andriy H.. "Spin Ferroquadrupolar Order in the Nematic Phase of FeSe." <i>Physical Review Letters,</i> 116, no. 24 (2016) American Physical Society: https://doi.org/10.1103/PhysRevLett.116.247203.https://hdl.handle.net/1911/94124We provide evidence that spin ferroquadrupolar (FQ) order is the likely ground state in the nonmagnetic nematic phase of stoichiometric FeSe. By studying the variational mean-field phase diagram of a bilinear-biquadratic Heisenberg model up to the 2nd nearest neighbor, we find the FQ phase in close proximity to the columnar antiferromagnet commonly realized in iron-based superconductors; the stability of the FQ phase is further verified by the density matrix renormalization group. The dynamical spin structure factor in the FQ state is calculated with flavor-wave theory, which yields a qualitatively consistent result with inelastic neutron scattering experiments on FeSe at both low and high energies. We verify that FQ can coexist with C4 breaking environments in the mean-field calculation, and further discuss the possibility that quantum fluctuations in FQ act as a source of nematicity.engArticle is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.Journal articlehttps://doi.org/10.1103/PhysRevLett.116.247203