From Event: SPIE Optical Engineering + Applications, 2018
By using both linear and nonlinear terahertz spectroscopy on epitaxial Bi and Bi1-xSbx thin films, we systematically investigated the linear and nonlinear terahertz dynamics of Dirac electrons. The linear terahertz transmittance was analyzed by the Drude model up to 50 THz, and then the plasma frequency and the damping constant were evaluated as functions of the film thickness and Sb-concentration. We found surface metallic state for Bi ultra-thin films, while semimetal to semiconductor crossover for Bi1-xSbx thin films. In the nonlinear terahertz spectroscopy, the terahertz transmittance increases with increasing the field strength, which could be assigned to the carrier acceleration along the Dirac-like band dispersion at the L point in the Brillouin zone. In addition, we observed the terahertz-induced absorption in terahertz-pump and terahertz-probe spectroscopy, which could be assigned to carrier generation due to Zener tunneling in Dirac band structure. The results demonstrate that Bi-related materials are promising candidates for future nonlinear terahertz devices.
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