Topological Dirac Surface States and Superconducting Pairing Correlations in PbTaSe2
Tay-Rong Chang1,2*, Peng-Jen Chen3,4, Guang Bian2,5, Shin-Ming Huang6,7, Hao Zheng2, Titus Neupert8, Raman Sankar9, Su-Yang Xu2, Ilya Belopolski2, Guoqing Chang6,7, BaoKai Wang6,7,10, Fangcheng Chou9, Arun Bansil10, Horng-Tay Jeng1,4, Hsin Lin6,7, M. Zahid Hasan2
1Physics, National Tsing Hua University, Hsinchu, Taiwan
2Physics, Princeton University, New Jersey, USA
3Physics, National Taiwan University, Taipei, Taiwan
4Physics, Academia Sinica, Taipei, Taiwan
5Physics and Astronomy, University of Missouri, Missouri, USA
6Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore
7Physics, National University of Singapore, Singapore, Singapore
8Princeton Center for Theoretical Science, Princeton University, New Jersey, USA
9Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
10Physics, Northeastern University, Massachusetts, USA
* presenting author:Tay-Rong Chang,
Superconductivity in topological band structures is a platform for realizing Majorana bound states and other exotic physical phenomena such as emergent supersymmetry. This potential nourishes the search for topological materials with intrinsic superconducting instabilities, in which Cooper pairing is introduced to electrons with helical spin texture such as the Dirac surface states of topological insulators, forming a time-reversal symmetric topological superconductor on the surface. We employ first-principles calculations and angle-resolved photoemission spectroscopy experiments to reveal that PbTaSe2, a noncentrosymmetric superconductor, possesses a nonzero Z2 topological invariant and fully spin-polarized Dirac surface states. Moreover, we analyze the phonon spectrum of PbTaSe2 to show how superconductivity emerges in this compound due to a stiffening of phonons by the Pb intercalation, which diminishes a competing charge-density-wave instability. By combining our findings on the topological band structure and the superconducting electron pairing, our work establishes PbTaSe2 as a stoichiometric superconductor with topological Dirac surface states. This type of intrinsic topological Dirac superconductors holds great promise for studying aspects of topological superconductors such as Majorana zero modes.

Keywords: Topological insulator , Superconductor, Topological Superconductor, spin-orbit coupling, first-principles