  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 BaTi2(As,Sb)2O, which is expressed as the three-dimensional
10-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 BaTi2(As,Sb)2O. 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.
