Dynamical nematic susceptibility from spin excitation anisotropy in quantum critical iron pnictides**

Quantum criticality in iron pnictides involves both the nematic and antiferromagnetic degrees of freedom[1,2], but the relationship between the two types of fluctuations has yet to be clarified. Here we study this problem in the presence of a small external uniaxial potential, which breaks the C4-symmetry in B1g sector. We establish an identity that connects the spin excitation anisotropy, which is the difference of the dynamical spin susceptibilities at (pi,0) and (0,pi) [3], with the dynamical magnetic susceptibility and static nematic susceptibility. Using this identity, we introduce a scaling procedure to determine the dynamical nematic susceptibility in the quantum critical regime, and illustrate the procedure for the case of the optimally Ni-doped BaFe2As2 [3]. We also provide the theoretical understanding for the so-determined dynamical nematic susceptibility. The implications of our results for the overall physics of the iron-based superconductors are discussed.



References:
[1] J. Dai, Q. Si, J. X. Zhu, and E. Abrahams, PNAS 106, 4118, (2009).
[2] J. Wu, Q. Si and E. Abrahams, Phys. Rev. B 93, 104515 (2016).
[3] Y. Song et al, Phys. Rev. B 92, 180504 (2015).