  Although, the long-standing debate on the resistivity anomaly in ZrTe$_{5}$
somewhat comes to an end, the exact topological nature of the electronic band
structure remains elusive till today. Theoretical calculations predicted that
bulk ZrTe$_{5}$ to be either a weak or a strong three-dimensional (3D)
topological insulator. However, the angle resolved photoemission spectroscopy
and transport measurements clearly demonstrate 3D Dirac cone state with a small
mass gap between the valence band and conduction band in the bulk. From the
magnetization and magneto-transport measurements on ZrTe$_{5}$ single crystal,
we have detected both the signature of helical spin texture from topological
surface state and chiral anomaly associated with the 3D Dirac cone state in the
bulk. This implies that ZrTe$_{5}$ is a novel 3D topological insulator having
massless Dirac fermionic excitation in its bulk gap state. Whereas, no 3D
topological insulator known in material science holds linear band dispersion in
its insulating bulk. Apart from the band topology, it is also apparent from the
resistivity and Hall measurements that the anomalous peak in the resistivity
can be shifted to a much lower temperature ($T$$<$2 K) by controlling impurity
and defects.
