title: Quantized Faraday and Kerr rotation and axion electrodynamics of a 3D topological insulator.
abstract: Topological insulators have been proposed to be best characterized as bulk magnetoelectric materials that show response functions quantized in terms of fundamental physical constants. Here, we lower the chemical potential of three-dimensional (3D) Bi2Se3films to ~30 meV above the Dirac point and probe their low-energy electrodynamic response in the presence of magnetic fields with high-precision time-domain terahertz polarimetry. For fields higher than 5 tesla, we observed quantized Faraday and Kerr rotations, whereas the dc transport is still semiclassical. A nontrivial Berry's phase offset to these values gives evidence for axion electrodynamics and the topological magnetoelectric effect. The time structure used in these measurements allows a direct measure of the fine-structure constant based on a topological invariant of a solid-state system.
authors.affiliation: Institute for Quantum Matter, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218, USA. liangwu@berkeley.edu npa@jhu.edu.
authors.forename: Liang
authors.initials: L
authors.lastname: Wu
authors.affiliation: Department of Materials Science and Engineering, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA.
authors.forename: M
authors.initials: M
authors.lastname: Salehi
authors.affiliation: Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA.
authors.forename: N
authors.initials: N
authors.lastname: Koirala
authors.affiliation: Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA.
authors.forename: J
authors.initials: J
authors.lastname: Moon
authors.affiliation: Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA.
authors.forename: S
authors.initials: S
authors.lastname: Oh
authors.affiliation: Institute for Quantum Matter, Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218, USA. liangwu@berkeley.edu npa@jhu.edu.
authors.forename: N P
authors.initials: NP
authors.lastname: Armitage