Abstract
High resolution Brillouin spectroscopy was used for the first time to study the dispersion and anisotropy of surface phonons in the single crystal of topological insulator Bi2Te3. Two surface acoustic waves have been observed, which distinguishes this material from other metals or nontransparent materials. The modes were assigned as Rayleigh waves. The obtained results were then simulated by Finite Element Method. The layered structure of the unit cell proposed in simulation reproduced quite well experimental results of the modes dispersion and anisotropy.
Highlights
High resolution Brillouin spectroscopy was used for the first time to study the dispersion and anisotropy of surface phonons in the single crystal of topological insulator B i2Te3
The electron phonon coupling (EPC) produces the abrupt change in the screening of lattice vibrations by conduction electron, leading to the well-known Kohn anomaly[7] manifested by a discontinuity in the derivative of the surface phonons dispersion relation that occurs at certain high symmetry points of the first Brillouin zone
The finite element method (FEM) method is based on division of the medium into small elements for which is possible to approximate the solution of wave equation by a linear function, which permits a transformation of the differential equation into a set of algebraic equations[23]
Summary
High resolution Brillouin spectroscopy was used for the first time to study the dispersion and anisotropy of surface phonons in the single crystal of topological insulator B i2Te3. Giraud and Egger analyzed the deformation potential linking Dirac fermions and acoustic phonons which allowed them to determine dispersion curves for low-frequency acoustic modes and their contribution to the electrical resistivity[8,9]. Another model, which inspired us to run the presented experiment was proposed by Thalmeier[10]. He replaced the global normal to the surface in the effective Dirac Hamiltonian by the local normal which depends on the position on the surface. This allowed to couple the Dirac states to the surface phonons dynamic
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