title: Spin polarization of gapped Dirac surface states near the topological phase transition in TlBi(S(1-x)Se(x))2.
abstract: We performed systematic spin- and angle-resolved photoemission spectroscopy of TlBi(S(1-x)Se(x))(2) which undergoes a topological phase transition at x ~ 0.5. In TlBiSe(2) (x = 1.0), we revealed a helical spin texture of Dirac-cone surface states with an intrinsic in-plane spin polarization of ~0.8. The spin polarization still survives in the gapped surface states at x > 0.5, although it gradually weakens upon approaching x = 0.5 and vanishes in the nontopological phase. No evidence for the out-of-plane spin polarization was found, irrespective of x and momentum. The present results unambiguously indicate the topological origin of the gapped Dirac surface states, and also impose a constraint on models to explain the origin of mass acquisition of Dirac fermions.
authors.affiliation: WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Souma
authors.forename: M
authors.initials: M
authors.lastname: Komatsu
authors.forename: M
authors.initials: M
authors.lastname: Nomura
authors.forename: T
authors.initials: T
authors.lastname: Sato
authors.forename: A
authors.initials: A
authors.lastname: Takayama
authors.forename: T
authors.initials: T
authors.lastname: Takahashi
authors.forename: K
authors.initials: K
authors.lastname: Eto
authors.forename: Kouji
authors.initials: K
authors.lastname: Segawa
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Ando