  We investigate the topological phase derived by time-reversal breaking fields
in a nonsymmorphic symmetry-protected two-dimensional Dirac semimetal. When the
nonsymmorphic symmetry is preserved even in the presence of the field, the
two-dimensional electronic states change into two distinct topological phases
with the insulating gap. One phase is well-known as quantum Hall states with
chiral edge modes accompanying the Hall current, but the other one is an
unconventional topological phase with helical edge modes in the absence of
time-reversal symmetry.
