title: Hidden Order and Dimensional Crossover of the Charge Density Waves in TiSe2.
abstract: Charge density wave (CDW) formation, a key physics issue for materials, arises from interactions among electrons and phonons that can also lead to superconductivity and other competing or entangled phases. The prototypical system TiSe2, with a particularly simple (2 × 2 × 2) transition and no Kohn anomalies caused by electron-phonon coupling, is a fascinating but unsolved case after decades of research. Our angle-resolved photoemission measurements of the band structure as a function of temperature, aided by first-principles calculations, reveal a hitherto undetected but crucial feature: a (2 × 2) electronic order in each layer sets in at ~232 K before the widely recognized three-dimensional structural order at ~205 K. The dimensional crossover, likely a generic feature of such layered materials, involves renormalization of different band gaps in two stages.
authors.affiliation: Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080, USA.|Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 104 South Goodwin Avenue, Urbana, Illinois 61801-2902, USA.|Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: P
authors.initials: P
authors.lastname: Chen
authors.affiliation: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.
authors.forename: Y-H
authors.initials: YH
authors.lastname: Chan
authors.affiliation: Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080, USA.|Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 104 South Goodwin Avenue, Urbana, Illinois 61801-2902, USA.
authors.forename: X-Y
authors.initials: XY
authors.lastname: Fang
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: S-K
authors.initials: SK
authors.lastname: Mo
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Hussain
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: A-V
authors.initials: AV
authors.lastname: Fedorov
authors.affiliation: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.|School of Physics, Georgia Institute of Technology, Atlanta, GA 30332, USA.|Department of Physics, National Taiwan University, Taipei 10617, Taiwan.
authors.forename: M Y
authors.initials: MY
authors.lastname: Chou
authors.affiliation: Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3080, USA.|Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, 104 South Goodwin Avenue, Urbana, Illinois 61801-2902, USA.|Department of Physics, National Taiwan University, Taipei 10617, Taiwan.
authors.forename: T-C
authors.initials: TC
authors.lastname: Chiang