Weak antilocalization in partially relaxed 200-nm HgTe films

The anomalous magnetoresistance caused by the weak antilocalization (WAL) effects in 200-nm HgTe films is experimentally studied. This system is a high quality 3D topological insulator that has much stronger spatial separation of surface states compare to previously studied thinner HgTe structures. However, in contrast to that films, the system under study is characterized by a reduced 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 positive 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 is caused by the increasing coupling between surface and bulk carriers.