Built-in electric field and its origin at the (111)R surface of topological insulators GeBi4Te7 and MnBi4Te7

The topological insulator GeBi 4 Te 7 belongs to a family of compounds consisting of alternating quintuple and septuple layers (QLs and SLs), and its surface electronic structure is determined by whether the crystal terminates with a QL or SL layer block. Using spatially and momentum-resolved photoelectron spectroscopy and STM/STS in the field emission resonance spectroscopy regime as well, we clearly revealed the charge redistribution between the QL and SL terminations, as evidenced by band bending. We attribute the charge redistribution to cation antisite defects in the SLs, which are electrically active and lead to an uncompensated surface charge. Our findings and the ability to manipulate the electronic properties of the surface have profound implications for the entire family of compounds, including the magnetic topological insulator Mn(Bi,Sb) 4 Te 7 .