Experimental verification of terahertz surface plasmon resonance using the Dirac electron system Bi₂Se_xTe_(3−x)

Although the surface plasmon resonance excited by a Dirac electron system has gained considerable attention in the terahertz region, studies have been limited to grating-coupling surface plasmon resonance (GC-SPR) in Bi₂Se₃. In this study, we experimentally demonstrated terahertz prism-coupled surface plasmon resonance (PC-SPR) and GC-SPR in topological insulator systems, viz. Bi₂Se₃ (GC-SPR), Bi₂Se₂Te (GC-SPR), and Bi₂Se₃ (PC-SPR). The physical properties measured using angle-resolved photoemission spectroscopy indicate that the presence of surface state near the Fermi level is insufficient for SPR excitation; linearity of the Dirac cone is essential for SPR excitation in the THz range.