title: Spectroscopic evidence for bulk-band inversion and three-dimensional massive Dirac fermions in ZrTe5.
abstract: Three-dimensional topological insulators (3D TIs) represent states of quantum matters in which surface states are protected by time-reversal symmetry and an inversion occurs between bulk conduction and valence bands. However, the bulk-band inversion, which is intimately tied to the topologically nontrivial nature of 3D Tis, has rarely been investigated by experiments. Besides, 3D massive Dirac fermions with nearly linear band dispersions were seldom observed in TIs. Recently, a van der Waals crystal, ZrTe5, was theoretically predicted to be a TI. Here, we report an infrared transmission study of a high-mobility [∼33,000 cm2/(V ⋅ s)] multilayer ZrTe5flake at magnetic fields (B) up to 35 T. Our observation of a linear relationship between the zero-magnetic-field optical absorption and the photon energy, a bandgap of ∼10 meV and a [Formula: see text] dependence of the Landau level (LL) transition energies at low magnetic fields demonstrates 3D massive Dirac fermions with nearly linear band dispersions in this system. More importantly, the reemergence of the intra-LL transitions at magnetic fields higher than 17 T reveals the energy cross between the two zeroth LLs, which reflects the inversion between the bulk conduction and valence bands. Our results not only provide spectroscopic evidence for the TI state in ZrTe5but also open up a new avenue for fundamental studies of Dirac fermions in van der Waals materials.
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; zgchen@iphy.ac.cn nlwang@pku.edu.cn.
authors.forename: Zhi-Guo
authors.initials: ZG
authors.lastname: Chen
authors.affiliation: International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China.
authors.forename: R Y
authors.initials: RY
authors.lastname: Chen
authors.affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, NY 11973.
authors.forename: R D
authors.initials: RD
authors.lastname: Zhong
authors.affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, NY 11973.
authors.forename: John
authors.initials: J
authors.lastname: Schneeloch
authors.affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, NY 11973.
authors.forename: C
authors.initials: C
authors.lastname: Zhang
authors.affiliation: Center for Functional Nanomaterials, Brookhaven National Lab, Upton, NY 11973.
authors.forename: Y
authors.initials: Y
authors.lastname: Huang
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.|QuTech, Delft University of Technology, Delft, 2600 GA, The Netherlands.
authors.forename: Fanming
authors.initials: F
authors.lastname: Qu
authors.affiliation: School of Physics and Technology, Wuhan University, Wuhan 430072, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Yu
authors.affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, NY 11973.
authors.forename: Q
authors.identifier: 0000-0002-1230-4832
authors.initials: Q
authors.lastname: Li
authors.affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, NY 11973.
authors.forename: G D
authors.initials: GD
authors.lastname: Gu
authors.affiliation: International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, China; zgchen@iphy.ac.cn nlwang@pku.edu.cn.|Collaborative Innovation Center of Quantum Matter, Beijing 100871, China.
authors.forename: N L
authors.initials: NL
authors.lastname: Wang
keywords: Dirac fermions; Landau levels; Zeeman splitting; band inversion; topological insulators