title: Observation of Dirac node formation and mass acquisition in a topological crystalline insulator.
abstract: In topological crystalline insulators (TCIs), topology and crystal symmetry intertwine to create surface states with distinct characteristics. The breaking of crystal symmetry in TCIs is predicted to impart mass to the massless Dirac fermions. Here, we report high-resolution scanning tunneling microscopy studies of a TCI, Pb(1-x)Sn(x)Se that reveal the coexistence of zero-mass Dirac fermions protected by crystal symmetry with massive Dirac fermions consistent with crystal symmetry breaking. In addition, we show two distinct regimes of the Fermi surface topology separated by a Van-Hove singularity at the Lifshitz transition point. Our work paves the way for engineering the Dirac band gap and realizing interaction-driven topological quantum phenomena in TCIs.
authors.affiliation: Department of Physics, Boston College, Chestnut Hill, MA 02467, USA.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Okada
authors.forename: Maksym
authors.initials: M
authors.lastname: Serbyn
authors.forename: Hsin
authors.initials: H
authors.lastname: Lin
authors.forename: Daniel
authors.initials: D
authors.lastname: Walkup
authors.forename: Wenwen
authors.initials: W
authors.lastname: Zhou
authors.forename: Chetan
authors.initials: C
authors.lastname: Dhital
authors.forename: Madhab
authors.initials: M
authors.lastname: Neupane
authors.forename: Suyang
authors.initials: S
authors.lastname: Xu
authors.forename: Yung Jui
authors.initials: YJ
authors.lastname: Wang
authors.forename: R
authors.initials: R
authors.lastname: Sankar
authors.forename: Fangcheng
authors.initials: F
authors.lastname: Chou
authors.forename: Arun
authors.initials: A
authors.lastname: Bansil
authors.forename: M Zahid
authors.initials: MZ
authors.lastname: Hasan
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Wilson
authors.forename: Liang
authors.initials: L
authors.lastname: Fu
authors.forename: Vidya
authors.initials: V
authors.lastname: Madhavan