title: The direct-to-indirect band gap crossover in two-dimensional van der Waals Indium Selenide crystals.
abstract: The electronic band structure of van der Waals (vdW) layered crystals has properties that depend on the composition, thickness and stacking of the component layers. Here we use density functional theory and high field magneto-optics to investigate the metal chalcogenide InSe, a recent addition to the family of vdW layered crystals, which transforms from a direct to an indirect band gap semiconductor as the number of layers is reduced. We investigate this direct-to-indirect bandgap crossover, demonstrate a highly tuneable optical response from the near infrared to the visible spectrum with decreasing layer thickness down to 2 layers, and report quantum dot-like optical emissions distributed over a wide range of energy. Our analysis also indicates that electron and exciton effective masses are weakly dependent on the layer thickness and are significantly smaller than in other vdW crystals. These properties are unprecedented within the large family of vdW crystals and demonstrate the potential of InSe for electronic and photonic technologies.
authors.affiliation: School of Physics &Astronomy, The University of Nottingham, Nottingham, NG7 2RD, UK.
authors.forename: G W
authors.initials: GW
authors.lastname: Mudd
authors.affiliation: Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 rue des Martyrs, 38042 Grenoble, France.
authors.forename: M R
authors.initials: MR
authors.lastname: Molas
authors.affiliation: National Graphene Institute, The University of Manchester, Manchester, M13 9PL, UK.
authors.forename: X
authors.initials: X
authors.lastname: Chen
authors.affiliation: National Graphene Institute, The University of Manchester, Manchester, M13 9PL, UK.
authors.forename: V
authors.initials: V
authors.lastname: Zólyomi
authors.affiliation: Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 rue des Martyrs, 38042 Grenoble, France.
authors.forename: K
authors.initials: K
authors.lastname: Nogajewski
authors.affiliation: School of Physics &Astronomy, The University of Nottingham, Nottingham, NG7 2RD, UK.
authors.forename: Z R
authors.initials: ZR
authors.lastname: Kudrynskyi
authors.affiliation: Institute for Problems of Materials Science, The National Academy of Sciences of Ukraine, Chernivtsi, 58001, Ukraine.
authors.forename: Z D
authors.initials: ZD
authors.lastname: Kovalyuk
authors.affiliation: Department of Physics, Tohoku University, Sendai 980-8578, Japan.
authors.forename: G
authors.initials: G
authors.lastname: Yusa
authors.affiliation: School of Physics &Astronomy, The University of Nottingham, Nottingham, NG7 2RD, UK.
authors.forename: O
authors.initials: O
authors.lastname: Makarovsky
authors.affiliation: School of Physics &Astronomy, The University of Nottingham, Nottingham, NG7 2RD, UK.
authors.forename: L
authors.initials: L
authors.lastname: Eaves
authors.affiliation: Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 rue des Martyrs, 38042 Grenoble, France.
authors.forename: M
authors.initials: M
authors.lastname: Potemski
authors.affiliation: National Graphene Institute, The University of Manchester, Manchester, M13 9PL, UK.
authors.forename: V I
authors.initials: VI
authors.lastname: Fal'ko
authors.affiliation: School of Physics &Astronomy, The University of Nottingham, Nottingham, NG7 2RD, UK.
authors.forename: A
authors.initials: A
authors.lastname: Patanè