Study of ultrafast dynamics in topological insulators by optical pump ultra-broadband mid-infrared probe spectroscopy

• Main Authors: Lin, Wen-Hao, 林文豪
• Other Authors: Luo, Chih-Wei
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/6rw49m

碩士 === 國立交通大學 === 電子物理系所 === 105 === We investigated the ultrafast carrier dynamics of topological insulators (TIs) including Bi2Te3-xSex and Sb2Te3-xSex (x=0,1) by the optical pump and ultra-broadband mid-IR probe spectroscopy, which was performed by using four-wave difference frequency generation. The mid-IR spectrum used in this study covers the region of 200-4000 cm-1 with pulse duration of 8.2 fs. Although both of Bi-series and Sb-series TIs have the surface states, they show totally different pattern in the transient reflectivity change (ΔR/R) spectrum. Moreover, by fitting with free carrier absorption model and optical conductivity of Kubo’s formula, the ultrafast dynamics of Bi2Te3-xSex are mainly dominated by the relaxation processes of free carrier at bulk and surface states. On the other hand, the ultrafast dynamics of Sb2Te3-xSex are caused by the shift of Fermi level.