Spin-driven nematicity, or the breaking of the point-group symmetry of the lattice without long-range magnetic order, is important in iron-based superconductors and beyond. From a symmetry point of view, nematic order can be described as a coherent locking of spin fluctuations in two interpenetrating Néel sublattices with ensuing nearest-neighbor bond order and an absence of static magnetism. We argued that the low-temperature state of the recently discovered superconductor BaTi2Sb2O is a strong candidate for a more exotic form of spin-driven nematic order, in which fluctuations occurring in four Néel sublattices promote both nearest- and next-nearest neighbor bond order.
Double-stage nematic bond ordering above double stripe magnetism: Application to BaTi2Sb2O
Emergent Ising degrees of freedom above a double-stripe magnetic ground state