title: Differentiation of Surface and Bulk Conductivities in Topological Insulators via Four-Probe Spectroscopy.
abstract: We show a new method to differentiate conductivities from the surface states and the coexisting bulk states in topological insulators using a four-probe transport spectroscopy in a multiprobe scanning tunneling microscopy system. We derive a scaling relation of measured resistance with respect to varying interprobe spacing for two interconnected conduction channels to allow quantitative determination of conductivities from both channels. Using this method, we demonstrate the separation of 2D and 3D conduction in topological insulators by comparing the conductance scaling of Bi2Se3, Bi2Te2Se, and Sb-doped Bi2Se3 against a pure 2D conductance of graphene on SiC substrate. We also quantitatively show the effect of surface doping carriers on the 2D conductance enhancement in topological insulators. The method offers a means to understanding not just the topological insulators but also the 2D to 3D crossover of conductance in other complex systems.
authors.affiliation: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Corentin
authors.initials: C
authors.lastname: Durand
authors.affiliation: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.|Department of Physics and the Quantum Theory Project, University of Florida , Gainesville, Florida 32611, United States.
authors.forename: X-G
authors.initials: XG
authors.lastname: Zhang
authors.affiliation: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Saban M
authors.initials: SM
authors.lastname: Hus
authors.affiliation: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Chuanxu
authors.initials: C
authors.lastname: Ma
authors.affiliation: Materials Science and Technology Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Michael A
authors.initials: MA
authors.lastname: McGuire
authors.affiliation: Department of Physics and Astronomy, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Yang
authors.initials: Y
authors.lastname: Xu
authors.affiliation: Department of Physics and Astronomy, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Helin
authors.initials: H
authors.lastname: Cao
authors.affiliation: Department of Physics and Astronomy, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Ireneusz
authors.initials: I
authors.lastname: Miotkowski
authors.affiliation: Department of Physics and Astronomy, Purdue University , West Lafayette, Indiana 47907, United States.|Birck Nanotechnology Center and School of Electrical and Computer Engineering, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Yong P
authors.initials: YP
authors.lastname: Chen
authors.affiliation: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: An-Ping
authors.initials: AP
authors.lastname: Li
keywords: Four-probe transport spectroscopy; dimensionality crossover; electrical transport; scanning tunneling microscopy; topological insulator; topological surface states