利用變溫飛秒光譜研究摻銅硒化鉍拓撲絕緣體之聲子動力學

Abstract

在本論文中，我們利用變溫飛秒光激發探測光譜來研究鉍、二硒化二鉍單晶及摻銅硒化鉍晶體的聲子動力學行為。藉由XRD實驗量測以及室溫下的OPOP實驗結果可知，摻雜入硒化鉍晶體的銅原子，主要是以鑲嵌的型式存在於五層結構與五層結構之間的間隙中。在變溫的實驗中，我們透過聲子頻率偏移以及線寬分析可以知道在硒化鉍晶體中的A1g1聲子的非和諧聲子耦合效應相較於A1g2聲子來的弱。隨著銅摻雜量的變化，我們發現銅原子的摻雜會造成晶格熱膨脹效應的增加以及A1g1聲子的非和諧聲子偶合效應的弱化。最後，我們觀察到摻銅硒化鉍晶體的A1g1聲子無論是在頻率偏移、線寬、弛緩週期以及振幅皆在100-150 K溫度範圍之間發生反常的變化。

Phonon dynamics in Bi, Bi2Se2, and CuxBi2Se3 (x = 0, 0.1, 0.125) single crystals has been investigated by temperature dependent femtosecond pump-probe reflectivity spectroscopy. By the results of XRD and OPOP measurements, we can infer that the Cu atoms in CuxBi2Se3 crystals are predominantly intercalated between the QLs. The temperature dependence of the A1g1 and A1g2 phonon frequency shift and linewidth is analyzed considering the material thermal expansion and anharnomic phonon coupling. The anharnomic phonon interaction of A1g1 phonon is weaker than A1g2 phonon in Bi2Se3 single crystal. The evolution of the A1g1 phonon frequency shift and linewidth for various Cu concentrations reveals that high lattice thermal expansion and weak anharnomic phonon interaction are induced by the Cu-intercalation. Finally the dramatic change of phonon frequency, linewidth, lifetime and amplitude in CuxBi2Se3 (x=0.1, 0.125) in temperature range 100-150 K have been observed.