  Topological electric quadrupole is a recently proposed concept that extends
the theory of electric polarization of crystals to higher orders. Such a
quadrupole phase supports topological states localized on both edges and
corners. In this work, we show that in a quadrupole phase of honeycomb lattice,
topological helical edge states and pseudo-spin-polarized corner states appear
by making use of a pseudo-spin degree of freedom related to point group
symmetry. Furthermore, we argue that a general condition for emergence of
helical edge states in a (pseudo-)spinful quadrupole phase is mirror or
time-reversal symmetry. Our results offers a way of generating topological
helical edge states without spin-orbital couplings.
