THz Generation and Detection on Dirac Fermions in Topological Insulators

Authors :: Luo, C. W.
Lee, C. C.
Chen, H. -J.
Tu, C. M.
Ku, S. A.
Tzeng, W. Y.
Yeh, T. T.
Chiang, M. C.
Wang, H. J.
Chu, W. C.
Lin, J. -Y.
Wu, K. H.
Juang, J. Y.
Kobayashi, T.
Cheng, C. -M.
Chen, C. -H.
Tsuei, K. -D.
Berger, H.
Sankar, R.
Chou, F. C.
Yang, H. D.
Publication Year :: 2013
Abstract: This study shows that a terahertz (THz) wave can be generated from the (001) surface of cleaved Bi$_{\textrm{2}}$Se$_{\textrm{3}}$ and Cu-doped Bi$_{\textrm{2}}$Se$_{\textrm{3}}$ single crystals using 800 nm femtosecond pulses. The generated THz power is strongly dependent on the carrier concentration of the crystals. An examination of the dependence reveals the two-channel free carrier absorption to which Dirac fermions are indispensable. Dirac fermions in Bi$_{\textrm{2}}$Se$_{\textrm{3}}$ are significantly better absorbers of THz radiation than bulk carriers at room temperature. Moreover, the characteristics of THz emission confirm the existence of a recently proposed surface phonon branch that is normalized by Dirac fermions.<br />Comment: 5 pages, 4 figures, 1 table