Journal
SCIENCE
Volume 354, Issue 6316, Pages 1124-1127Publisher
AMER ASSOC ADVANCEMENT SCIENCE
DOI: 10.1126/science.aaf5541
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Funding
- Army Research Office [W911NF-15-1-0560]
- Gordon and Betty Moore Foundation [GBMF2628]
- NSF [DMR-1308142, EFMA-1542798]
- Gordon and Betty Moore Foundation EPiQS Initiative [GBMF4418]
- Emerging Frontiers & Multidisciplinary Activities
- Directorate For Engineering [1542798] Funding Source: National Science Foundation
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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 similar 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.
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