2016/03/31 by Liang Wu, M. Salehi, N. Koirala +3 · 2 citations
Physics and Astronomy · #cond-mat.mes-hall #cond-mat.mtrl-sci #cond-mat.str-el
paper · pdf · doi:10.1126/science.aaf5541
published as Science 354, 1124-1127 (2016) · A shortened version has been published in Science. Discussion on AC quantum Hall effect without involving edge states is added
arxiv created 2016/12/05 · arxiv updated 2016/12/07
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) Bi2Se3 films 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 T, we observed quantized Faraday and Kerr rotations, whereas the DC transport is still semi-classical. A non-trivial Berry 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.