2013/10/28 by Y. H. Wang, H. Steinberg, P. Jarillo-Herrero +1 · 6 citations
Physics and Astronomy · #cond-mat.mes-hall
paper · pdf · doi:10.1126/science.1239834
published as Science,342,453 (2013) · 23 pages including supplementary materials
arxiv created 2013/10/28 · arxiv updated 2013/10/29
The unique electronic properties of the surface electrons in a topological insulator are protected by time-reversal symmetry. Circularly polarized light naturally breaks time-reversal symmetry, which may lead to an exotic surface quantum Hall state. Using time- and angle-resolved photoemission spectroscopy, we show that an intense ultrashort mid-infrared pulse with energy below the bulk band gap hybridizes with the surface Dirac fermions of a topological insulator to form Floquet-Bloch bands. These photon dressed surface bands exhibit polarization-dependent band gaps at avoided crossings. Circularly polarized photons induce an additional gap at the Dirac point, which is a signature of broken time-reversal symmetry on the surface. These observations establish the Floquet-Bloch bands in solids and pave the way for optical manipulation of topological quantum states of matter.