Scanning tunneling microscopy of topological insulator Bi$_2$Te$_2$Se

Using scanning tunneling microscopy, we study a prototypical topological insulator Bi$_2$Te$_2$Se having suppressed bulk carrier density. Landau level states of its topological surface state remarkably exhibit hysteresis behavior, which shift in energy controllably with the limits of ramping bias, forming hysteresis loops thereafter. The observed hysteresis behavior is attributed to the interplay between a tip-induced gating effect and an impurity-generated random charging effect. This provides a new avenue to controlling the topological surface state.