拓樸絕緣體碲化銻薄膜之兆赫波輻射光譜學研究

Abstract

在這本論文中，我們利用超快雷射激發拓樸絕緣體碲化銻薄膜， 使其輻射具有旋光相依性的兆赫波。我們藉由不同偏振光入射下，觀 察到兆赫波的極性會有翻轉之現象。這個翻轉的現象，和旋光相依性 的光電流行為是非常吻合的。接著採用兆赫波時域波形的分離及重組 方法，將原本混合在一起的三個物理機制個別分離出來，這三個物理 機制分別為圓偏振光致自旋電流效應、線偏振光致自旋電流效應、光 子牽引效應。此外，我們可以從時間解析與角度解析光電子能譜的光 激載子動力學结果得到相對應的瞬時電流，在考慮遠場下，此瞬時電 流所產生的電磁輻射與我們的實驗結果一致。 最後，我們的研究不僅證明了拓樸絕緣體的表面態可輻射出具有 旋光相依性的兆赫波，而且本論文的成果也進一步說明了兆赫波輻射 光譜學是研究自旋電子學相關主題的新利器。

In this thesis, we show the helicity-dependent terahertz emissions from topological insulator (TI) Sb2Te3 thin films by ultrafast optical excitation. We observed the polarity-reversal of the emitted THz radiation as the helicity of optical pulses reverses. The observed phenomenon is consistent with the characteristics of the helicity-dependent photocurrent on TIs. Employing a decomposition-recombination procedure in time domain, the individual contributions of circular photogalvanic effect, linear photogalvanic effect and photon drag effect are revealed completely. Additionally, based on the Tr-ARPES results and considering transient-current radiation as well as far-field diffraction, our results are the same as that from Tr-ARPES results. Finally, our results not only demonstrate that helicity-dependent THz emission originated from topological insulator surface states can be manipulated by ultrafast optical pulses but also pave a way towards applications of THz emission spectroscopy on spintronics.