Kohn anomaly and topological surface state-derived Fermi nesting of the topological superconducting material PbTaSe₂

Syu-You Guan^1*, Peng-Jen Chen⁵, Ye-Shun Lan³, Raman Sankar¹, Fangcheng Chou², Horng-Tay Jeng³, Chia-Seng Chang^1,4, Tien-Ming Chuang¹

¹Institute of Physics, Academia Sinica, Taipei, Taiwan
²Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
³Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
⁴Department of Physics, National Taiwan University, Taipei, Taiwan
⁵School of Electronic and Electrical Engineering, Zhaoqing University, Zhaoqing, China

* Presenter:Syu-You Guan, email:r95222038@gmail.com

Topological superconductors, in which Majorana fermions emerge, are on the forefront of condensed matter physics research. PbTaSe₂ is one of the prime intrinsic topological superconductors. While its crystal structure allows two different surface terminations after cleavage, previous spectroscopic experiments have focused only on the Pb-terminated surface. Here, we report a comprehensive study on the electronic structure of Se-terminated 2×2 surface by scanning tunneling microscopy and first-principles calculations. Surface phonon calculations for the first-time demonstrate that the surface 2×2 reconstruction is governed by the Kohn anomaly from the topological surface state (TSS) - derived Femi nesting, which leads to a band folding on the TSS and a gap opening on the TSS between E = 130 and E = 190 meV. Despite this, the TSS still exhibits the helical spin polarization around the Fermi level and becomes superconducting at bulk T_c. Upon the application of the magnetic field, a zero energy bound state can be observed at the vortex cores. Our results demonstrate that the Se-terminated 2×2 surface also serves as an ideal platform for the proximity-induced topological superconductivity based on the Fu-Kane model as well as for the study of the interplay between the electron-phonon coupling, charge order, the TSS and topological superconductivity.

Keywords: scanning tunneling microscopy, topological superconductivity, charge density wave, Fermi nesting, Kohn anomaly