Theoretical prediction of nematic orbital-ordered state in the Ti oxypnictide superconductorBaTi2(As,Sb)2O

The electronic nematic state without magnetization emerges in various strongly correlated metals such as Fe-based and cuprate superconductors. To understand this universal phenomenon, we focus on the nematic state in Ti oxypnictide ${\mathrm{BaTi}}₂{(\mathrm{As},\mathrm{Sb})}₂\mathrm{O}$, which is expressed as the three-dimensional ten-orbital Hubbard model. The antiferromagnetic fluctuations are caused by the Fermi surface nesting. Interestingly, we find the spin-fluctuation-driven orbital order due to the strong orbital-spin interference, which is described by the Aslamazov-Larkin vertex correction (AL-VC). The predicted intra-unit-cell nematic orbital order is consistent with the recent experimental reports on ${\mathrm{BaTi}}₂{(\mathrm{As},\mathrm{Sb})}₂\mathrm{O}$. Thus, the spin-fluctuation-driven orbital order due to the AL-VC mechanism is expected to be universal in various two- and three-dimensional multiorbital metals.