title: Dimensional Effects on the Charge Density Waves in Ultrathin Films of TiSe2.
abstract: Charge density wave (CDW) formation in solids is a critical phenomenon involving the collective reorganization of the electrons and atoms in the system into a wave structure, and it is expected to be sensitive to the geometric constraint of the system at the nanoscale. Here, we study the CDW transition in TiSe2, a quasi-two-dimensional layered material, to determine the effects of quantum confinement and changing dimensions in films ranging from a single layer to multilayers. Of key interest is the characteristic length scale for the transformation from a two-dimensional case to the three-dimensional limit. Angle-resolved photoemission spectroscopy (ARPES) measurements of films with thicknesses up to six layers reveal substantial variations in the energy structure of discrete quantum well states; however, the temperature-dependent band gap renormalization converges at just three layers. The results indicate a layer-dependent mixture of two transition temperatures and a very-short-range CDW interaction within a three-dimensional framework.
authors.affiliation: Department of Physics, University of Illinois at Urbana-Champaign , 1110 West Green Street, Urbana, Illinois 61801-3080, United States.|Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign , 104 South Goodwin Avenue, Urbana, Illinois 61801-2902, United States.|Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
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, United States.|Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign , 104 South Goodwin Avenue, Urbana, Illinois 61801-2902, United States.
authors.forename: M-H
authors.initials: MH
authors.lastname: Wong
authors.affiliation: Department of Physics, University of Illinois at Urbana-Champaign , 1110 West Green Street, Urbana, Illinois 61801-3080, United States.|Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign , 104 South Goodwin Avenue, Urbana, Illinois 61801-2902, United States.
authors.forename: X-Y
authors.initials: XY
authors.lastname: Fang
authors.affiliation: Institute of Atomic and Molecular Sciences, Academia Sinica , Taipei 10617, Taiwan.|School of Physics, Georgia Institute of Technology , Atlanta, Georgia 30332, United States.|Department of Physics, National Taiwan University , Taipei 10617, Taiwan.
authors.forename: M Y
authors.initials: MY
authors.lastname: Chou
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: S-K
authors.initials: SK
authors.lastname: Mo
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Z
authors.initials: Z
authors.lastname: Hussain
authors.affiliation: Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: A-V
authors.initials: AV
authors.lastname: Fedorov
authors.affiliation: Department of Physics, University of Illinois at Urbana-Champaign , 1110 West Green Street, Urbana, Illinois 61801-3080, United States.|Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign , 104 South Goodwin Avenue, Urbana, Illinois 61801-2902, United States.|Department of Physics, National Taiwan University , Taipei 10617, Taiwan.
authors.forename: T-C
authors.initials: TC
authors.lastname: Chiang
keywords: Charge density wave; phase transition; quantum confinement; titanium diselenide; transition metal dichalcognides; ultrathin film