Relocation of the topological surface state of Bi$_{2}$Se$_{3}$ beneath   the surface by Ag intercalation
  We studied the Ag-intercalated 3D topological insulator Bi$_{2}$Se$_{3}$ by scanning tunneling microscopy/spectroscopy and angle-resolved photoemission spectroscopy, combined with a first principles calculations. We demonstrate that silver atoms deposited on the surface of Bi$_{2}$Se$_{3}$ are intercalated between the quintuple layer (QL) units of the crystal, causing a expansion of the van der Waals gaps and the detachment of topmost QLs from the bulk crystal. This leads to a relocation (in the real space) of the the topological state beneath the detached quintuple layers, accompanied by the emergence of parabolic and "M-shaped" trivial bands localized above the relocated topological states. These novel findings open a pathway to the engineering of Dirac fermions shielded from the ambient contamination and may facilitate the realization of fault-tolerant quantum devices. 
M. Ye, S. V. Eremeev, K. Kuroda, M. Nakatake, S. Kim, Y. Yamada, E. E.   Krasovskii, E. V. Chulkov, M. Arita, H. Miyahara, T...
cond-mat.mes-hall