  The introduction of magnetic order on the surface of topological insulators
in general breaks the two-dimensional character of topological surface state
(TSS). Once the TSS disappears, it is improbable to restore the topological
surface properties. In this report, we demonstrate that it is possible to
restore the inherent TSS by ultra-high vacuum annealing. Starting from an
antiferromagnetic Gd-doped Bi2Te3, that has surface state gap without TSS
properties, after annealing we observed the gap closing as well as typical TSS
features in physical properties. The microscopic mechanism of atomic migration
and TSS restoration by annealing process is unraveled by the combination of
scanning tunneling microscopy measurements and density functional theory
calculations. This approach to control the surface of topological insulators
and stabilize the TSS simply by vacuum annealing provides a new platform
towards the exploitation of their topological properties.
