title: Quantum capacitance in topological insulators.
abstract: Topological insulators show unique properties resulting from massless, Dirac-like surface states that are protected by time-reversal symmetry. Theory predicts that the surface states exhibit a quantum spin Hall effect with counter-propagating electrons carrying opposite spins in the absence of an external magnetic field. However, to date, the revelation of these states through conventional transport measurements remains a significant challenge owing to the predominance of bulk carriers. Here, we report on an experimental observation of Shubnikov-de Haas oscillations in quantum capacitance measurements, which originate from topological helical states. Unlike the traditional transport approach, the quantum capacitance measurements are remarkably alleviated from bulk interference at high excitation frequencies, thus enabling a distinction between the surface and bulk. We also demonstrate easy access to the surface states at relatively high temperatures up to 60 K. Our approach may eventually facilitate an exciting exploration of exotic topological properties at room temperature.
authors.affiliation: Department of Electrical and Computer Engineering, Iowa State University, Ames, Iowa, USA. Faxian@iastate.edu
authors.forename: Faxian
authors.initials: F
authors.lastname: Xiu
authors.forename: Nicholas
authors.initials: N
authors.lastname: Meyer
authors.forename: Xufeng
authors.initials: X
authors.lastname: Kou
authors.forename: Liang
authors.initials: L
authors.lastname: He
authors.forename: Murong
authors.initials: M
authors.lastname: Lang
authors.forename: Yong
authors.initials: Y
authors.lastname: Wang
authors.forename: Xinxin
authors.initials: X
authors.lastname: Yu
authors.forename: Alexei V
authors.initials: AV
authors.lastname: Fedorov
authors.forename: Jin
authors.initials: J
authors.lastname: Zou
authors.forename: Kang L
authors.initials: KL
authors.lastname: Wang