Observation of Floquet-Bloch States on the Surface of a Topological Insulator
Author(s)Wang, Y. H.; Steinberg, Hadar; Jarillo-Herrero, Pablo; Gedik, Nuh
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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 midinfrared 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.
DepartmentMassachusetts Institute of Technology. Department of Physics
Wang, Y. H., H. Steinberg, P. Jarillo-Herrero, and N. Gedik. “Observation of Floquet-Bloch States on the Surface of a Topological Insulator.” Science 342, no. 6157 (October 25, 2013): 453–457.
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