Converse Flexoelectricity of Low-Dimensional Bismuth Selenite Revealed by Piezoresponse Force Microscopy (PFM)

Many kinds of two-dimensional (2D) van der Waals (vdW) have been demonstrated to exhibit electromechanical coupling effects, which makes them promising candidates for next-generation devices. In this study, we experimentally investigate the electromechanical coupling of low dimensional vdW topological insulators (TIs) with a centrosymmetric crystal structure, where a binary compound, bismuth selenite $\left(\mathrm{Bi}_{2}\mathrm{Se}_{3}\right)$, is taken as an example. The results of piezoresponse force microscope (PFM) tests on the Bi2Se3 nanoflakes show that the material exhibits both out-of-plane and in-plane electromechanical responses.