Surface vibrational modes of the topological insulator Bi${}_2$Se${}_3$ observed by Raman spectroscopy

Abstract

We present polarization resolved Raman scattering study of surface vibration modes in the topological insulator Bi${}_2$Se${}_3$ single crystal and thick films. Besides the four Raman active bulk phonons, we observed four additional modes with much weaker intensity and slightly lower energy than the bulk counterparts. Using symmetry analysis, we assigned these additional modes to out-of-plane surface phonons. Comparing with first principle calculations, we conclude that the appearance of these modes is due to $c$-axis lattice distortion and van der Waals gap expansion near the crystal surface. Two of the surface modes at 60 and 173 cm${}^{-1}$ are associated with Raman active $A_{1g}$ bulk phonon modes, the other two at 136 and 158 cm${}^{-1}$ are associated with infrared active bulk phonons with $A_{2u}$ symmetry. The latter become Raman allowed due to reduction of crystalline symmetry from $D_{3d}$ in the bulk to $C_{3v}$ on the crystal surface. In particular, the 158 cm${}^{-1}$ surface phonon mode shows a Fano lineshape under resonant excitation, suggesting interference in the presence of electron-phonon coupling of the surface excitations.

arXiv comment11 pages, 5 figures and 3 tables

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• Lattice dynamics of the excitonic insulator Ta${}_2$Ni(Se${}_{1-x}$S${}_x$)${}_5$
• Surface Phonons in the Topological Insulators Bi2Se3 and Bi2Te3
• Influence of local symmetry on lattice dynamics coupled to topological surface states
• Anomalous magneto-elastic coupling in Au-doped BaFe2As2
• Electronic and Vibrational Excitations on the Surface of the Three-Dimensional Topological Insulator Bi${}_2$Te${}_{3-x}$Se${}_x$ (x = 0, 2, 3)
• Structural and magneto-transport studies of iron intercalated Bi2Se3 single crystals
• Vibrational Properties of the Bi2Se3 Orthorhombic Metastable Phase
• From classical to quantum regime of topological surface states via defect engineering
• Non-trivial phonon dynamics and significant electron-phonon coupling of the high frequency modes in a Dirac semimetal
• Introducing antiferromagnetic ordering on the surface states of Bi2Se3 topological insulator by Europium doping
• Evidence for atomic-scale vibron-mediated electron bunching