Influence of local symmetry on lattice dynamics coupled to topological surface states

• Published in: Physical review. B 2023-01, Vol.107 (1), Article 014305
• Main Authors: Sobota, Jonathan A., Teitelbaum, Samuel W., Huang, Yijing, Querales-Flores, José D., Power, Robert, Allen, Meabh, Rotundu, Costel R., Bailey, Trevor P., Uher, Ctirad, Henighan, Tom, Jiang, Mason, Zhu, Diling, Chollet, Matthieu, Sato, Takahiro, Trigo, Mariano, Murray, Éamonn D., Savić, Ivana, Kirchmann, Patrick S., Fahy, Stephen, Reis, David A., Shen, Zhi-Xun
• Format: Article
• Language: English
• Subjects: CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; electron-phonon coupling; phonons; time and angle resolved photoemission spectroscopy; topological materials; ultrafast pump-probe spectroscopy; x-ray diffraction
• ISSN: 2469-9950; 2469-9969
• DOI: 10.1103/PhysRevB.107.014305

Herein we investigate coupled electron-lattice dynamics in the topological insulator Bi2Te3 with time-resolved photoemission and time-resolved x-ray diffraction. It is well established that coherent phonons can be launched by optical excitation, but selection rules generally restrict these modes to zone-center wave vectors and Raman-active branches. We find that the topological surface state couples to additional modes, including a continuum of surface-projected bulk modes from both Raman and infrared branches, with possible contributions from surface-localized modes when they exist. Our calculations show that this surface vibrational spectrum occurs naturally as a consequence of the translational and inversion symmetries broken at the surface, without requiring the splitting-off of surface-localized phonon modes. The generality of this result suggests that coherent phonon spectra are useful by providing unique fingerprints for identifying surface states in more controversial materials. These effects may also expand the phase space for tailoring surface state wave functions via ultrafast optical excitation.