%0 Journal Article
%T Observation of Floquet-Bloch states on the surface of a topological insulator
%A Y. H. Wang
%A H. Steinberg
%A P. Jarillo-Herrero
%A N. Gedik
%J Physics
%D 2013
%I arXiv
%R 10.1126/science.1239834
%X 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.
%U http://arxiv.org/abs/1310.7563v1