Br‐Vacancies Induced Variable Ranging Hopping Conduction in High‐Order Topological Insulator Bi₄Br₄

The defects have a remarkable influence on the electronic structures and the electric transport behaviors of the matter, providing the additional means to engineering their physical properties. In this work, a comprehensive study on the effect of Br‐vacancies on the electronic structures and transport behaviors in the high‐order topological insulator Bi 4 Br 4 is performed by the combined techniques of the scanning tunneling microscopy (STM), angle‐resolved photoemission spectroscopy (ARPES), and physical properties measurement system along with the first‐principle calculations. The STM results show the defects on the cleaved surface of a single crystal and reveal that the defects are correlated to the Br‐vacancies with the support of the simulated STM images. The role of the Br‐vacancies in the modulation of the band structures has been identified by ARPES spectra and the calculated energy‐momentum dispersion. The relationship between the Br‐vacancies and the semiconducting‐like transport behaviors at low temperature has been established, implying a Mott variable ranging hopping conduction in Bi 4 Br 4 . The work not only resolves the unclear transport behaviors in this matter, but also paves a way to modulate the electric conduction path by the defects engineering.