  The phase transition between type-I and type-II Dirac semimetals will reveal
a series of significant physical properties because of their completely
distinct electronic, optical and magnetic properties. However, no mechanism and
materials have been proposed to realize the transition to date. Here, we
propose that the transition can be realized in two-dimensional (2D) materials
consisting of zigzag chains, by tuning external strains. The origination of the
transition is that some orbital interactions in zigzag chains vary drastically
with structural deformation, which changes dispersions of the corresponding
bands. Two 2D nanosheets, monolayer PN and AsN, are searched out to confirm the
mechanism by using first-principles calculations. They are intrinsic type-I or
type-II Dirac materials, and transit to another type of Dirac materials by
external strains. In addition, a possible routine is proposed to synthesize the
new 2D structures.
