What drives electronic nematic order in iron-based superconductors
In plain words
Electrons in iron-based materials spontaneously choose one crystal direction; it is debated whether magnetism, orbital occupation, or chemical bonds drive this choice, especially in FeSe where no magnetism follows.
Precise statement
In iron pnictides and FeSe, determine whether $B1g$ electronic nematic order (measured by elastoresistance and Raman) is driven by spin fluctuations (vestigial order of stripe magnetism), by orbital order ($n_{xz} - n_{yz}$), or by bond order, and in particular explain nematic order at $T_s \sim 90\,\mathrm{K}$ without magnetic order in FeSe. An answer is a theory consistent with the neutron spin-fluctuation spectrum, the ARPES orbital splitting and the absence of magnetic order in FeSe.
What would settle it
A calculation reproducing $T_s$, the orbital splitting and the spin-fluctuation spectrum of FeSe and BaFe2As2 with one set of interaction parameters.