Observation of floquet-bloch states on the surface of a topological insulator

Y. H. Wang, H. Steinberg, P. Jarillo-Herrero, N. Gedik*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

875 Scopus citations


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.

Original languageAmerican English
Pages (from-to)453-457
Number of pages5
Issue number6157
StatePublished - 2013
Externally publishedYes


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