title: Competing weak localization and weak antilocalization in ultrathin topological insulators.
abstract: We demonstrate evidence of a surface gap opening in topological insulator (TI) thin films of (Bi(0.57)Sb(0.43))(2)Te(3) below six quintuple layers through transport and scanning tunneling spectroscopy measurements. By effective tuning the Fermi level via gate-voltage control, we unveil a striking competition between weak localization and weak antilocalization at low magnetic fields in nonmagnetic ultrathin films, possibly owing to the change of the net Berry phase. Furthermore, when the Fermi level is swept into the surface gap of ultrathin samples, the overall unitary behaviors are revealed at higher magnetic fields, which are in contrast to the pure WAL signals obtained in thicker films. Our findings show an exotic phenomenon characterizing the gapped TI surface states and point to the future realization of quantum spin Hall effect and dissipationless TI-based applications.
authors.affiliation: Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA.
authors.forename: Murong
authors.initials: M
authors.lastname: Lang
authors.forename: Liang
authors.initials: L
authors.lastname: He
authors.forename: Xufeng
authors.initials: X
authors.lastname: Kou
authors.forename: Pramey
authors.initials: P
authors.lastname: Upadhyaya
authors.forename: Yabin
authors.initials: Y
authors.lastname: Fan
authors.forename: Hao
authors.initials: H
authors.lastname: Chu
authors.forename: Ying
authors.initials: Y
authors.lastname: Jiang
authors.forename: Jens H
authors.initials: JH
authors.lastname: Bardarson
authors.forename: Wanjun
authors.initials: W
authors.lastname: Jiang
authors.forename: Eun Sang
authors.initials: ES
authors.lastname: Choi
authors.forename: Yong
authors.initials: Y
authors.lastname: Wang
authors.forename: Nai-Chang
authors.initials: NC
authors.lastname: Yeh
authors.forename: Joel
authors.initials: J
authors.lastname: Moore
authors.forename: Kang L
authors.initials: KL
authors.lastname: Wang