Weak localization effects as evidence for bulk quantization in Bi sub(2)Se sub(3) thin films

Strong spin-orbit coupling in topological insulators results in the ubiquitously observed weak antilocalization feature in their magnetoresistance. Here we present magnetoresistance measurements in ultrathin films of the topological insulator Bi sub(2)Se sub(3) and show that in the two-dimensional quantum limit, in which the topological insulator bulk becomes quantized, an additional negative magnetoresistance feature appears. Detailed analysis associates this feature with weak localization of the quantized bulk channels, thus providing evidence for this quantization. Examination of the dephasing fields at different temperatures indicates different scattering mechanism in the bulk vs the surface states.