  With topologcial semimetal developing, semimetal with nodal-line ring comes
into people's vision as a powerful candidate for practical application of
topological devices. We propose a method using ultracold atoms in
two-dimensional amplitude-shaken bipartite hexagonal optical lattice to
simulate nodal-line semimetal, which can be achieved in experiment by attaching
one triangular optical lattice to a hexangonal optical lattice and periodically
modulating the intensity and position of the triangular lattice. By amplitude
shaking, a time-reversal-symmetry-unstable mode is introduced into the
bipartite optical lattice, and then the nodal-line semimetal is gotten by
adjusting the proportion of such mode and the trivial mode of hexagonal
lattice. Through calculating the energy spectrum of effective Hamiltonian, the
transformation from Dirac semimetal to nodal-line semimetal in pace with
changing shaking parameters is observed. We also study the change of Berry
curvature and Berry phase in the transformation, which provides guidance on
measuring the transformation in experiment. By analyzing the symmetry of the
system, the emergence of the time-reversal-symmetry-unstable mode is
researched. This proposal provides a way to research the pure nodal-line
semimetal without the influence of other bands, which may contribute to the
study of those unique features of surface states and bulk states of nodal-line
semimetal.
