Mechanical dissipation via image potential states on Bi₂Te₃surface

We studied the frictional response of the Bi₂Te₃ (0001) crystal by means of combined pendulum atomic force microscopy (AFM) and scanning tunneling microscopy (STM). While Joule dissipation is suppressed due to a topologically protected surface state, another dissipation mechanism due to single electron tunneling into image potential states (IPS), which are slightly above the Bi₂Te₃ surface is observed. Dissipation peaks are localized at relatively large voltages as expected for IPS and observed to be shifted to even higher voltages as tip-sample distance increases. We observed that the application of a magnetic field leads to the breakdown of the topological protection of the surface states and restores the expected Joule dissipation process. [1] – D. Yildiz, et al., Nat. Mater. 18, 1201-1206, (2019).