  The anomalous magnetoresistance caused by the weak antilocalization (WAL)
effects in 200-nm HgTe films is experimentally studied. The film is a high
quality 3D topological insulator with much stronger spatial separation of
surface states than in previously studied thinner HgTe structures. However, in
contrast to that films, the system under study is characterized by a reduced
partial strain resulting in an almost zero bulk energy gap. It has been shown
that at all positions of the Fermi level the system exhibits a WAL conductivity
correction superimposed on classical parabolic magnetoresistance. Since high
mobility of carriers, the analysis of the obtained results was performed using
a ballistic WAL theory. The maximum of the WAL conductivity correction
amplitude was found at a Fermi level position near the bulk energy gap
indicating to full decoupling of the surface carriers in these conditions. The
WAL amplitude monotonously decreases when the density of either bulk electrons
or holes increases that results from the increasing coupling between surface
and bulk carriers.
