Controlled Filling of Landau Levels on the 2D Topological Insulator Bi₂Te₃ Using Magnetic Force Microscopy

In this work well defined, stoichiometric two-dimensional (2D) nanoplates of the topological insulator, Bi₂Te₃, were imaged using magnetic force microscopy (MFM) and atomic force microscopy (AFM). Nanoplates with a diameter range of 0.5 to 1.5µm and ~6-15nm thick were supported on highly ordered pyrolytic graphite (HOPG) and examined in air. Magnetic force contrast localized to the perimeter of the nanoplates was observed at room temperature. The relative strength of the edge-fields was measured at variable heights detailing a unique relationship between the dynamics of the magnetic cantilever and the nanoplates under observation. We suggest time-reversal symmetry breaking in the Bi₂Te₃ nanocrystal from the field of the imaging magnetic cantilever which results in induced, topologically-protected currents. The addition of an applied DC bias to the tip enables the controlled filling of Landau levels by lowering or raising the fermi level. Previous studies suggest Bi₂Te₃ nanoplates of similar proportions to lie within the 3D topological insulator family and therefore harbor 2D surface states, however, based on the nature of the contrast seen in the MFM, electron energy loss spectroscopy (EELS), and our synthesis method we argue these nanoplates fall within the 2D topological insulator family. These studies reveal the existence of persistent currents in our 2D Bi₂Te₃ system at room temperature and point to MFM as a powerful tool for probing such topologically protected quantum spin hall states.