  We study the magnetization plateau state of the three-leg spin-1/2 tube in
the strong rung coupling region, where S_3-symmetry breakings and low-energy
chirality degree of freedom play crucial roles. On the basis of the effective
chirality model and density matrix renormalization group, we clarify that, as
the leg coupling increases, the chirality liquid with gapless non-magnetic
excitations, the spin imbalance phase and the vector-spin-chirality ordered
phase emerge without closing the plateau spin gap. The relevance of these
results to experiments is also discussed.
