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We investigate via density functional theory calculations the recently reported unusual nematic behavior of heavily hole-doped pnictides AFe₂As₂ (A = Rb, Cs) [1,2]. In contrast to the B_2g nematic order of the parent 122 compounds, characterized by unequal Fe-Fe bonds, in the former systems nematic order is observed in the B_1g channel, characterized by unequal Fe-As-Fe bonds. We attribute this behavior to the evolution of the magnetic ground state along the compound series Sr_1-xRb_xFe₂As₂, from single stripes for small x to double stripes for large x. Our simulations using the reduced Stoner theory show that fluctuations of Fe moments are essential for the stability of the double-stripe configuration. We discuss the relationship between these magnetic orderings and the nature of nematicity in terms of vestigial orders [3].

References
1. X. Liu et al., arXiv:1803.07304 (2018).
2. S. Onari and H. Kontani, arXiv:1809.08017 (2018).
3. V. Borisov et al. In preparation.