  The recently discovered topological Dirac semimetal represents a new exotic
quantum state of matter. Topological Dirac semimetals can be viewed as three
dimensional analogues of graphene, in which the Dirac nodes are protected by
crystalline symmetry. It has been found that quantum confinement effect can gap
out Dirac nodes and convert Dirac semimetal to a band insulator. The band
insulator is either normal insulator or quantum spin Hall insulator depending
on the thin film thickness. We present the study of disorder effects in thin
film of Dirac semimetals. It is found that moderate Anderson disorder strength
can drive a topological phase transition from normal band insulator to
topological Anderson insulator in Dirac semimetal thin film. The numerical
calculation based on the model parameters of Dirac semimetal Na$_{3}$Bi shows
that in the topological Anderson insulator phase a quantized conductance
plateau occurs in the bulk gap of band insulator, and the distributions of
local currents further confirm that the quantized conductance plateau arises
from the helical edge states induced by disorder. Finally, an effective medium
theory based on Born approximation fits the numerical data.
