Scanning Tunneling Microscopy Observation of Topology-Protecting Systematic Vacancy Superstructure in the Dirac Semimetal Cd3As2
Christopher J. Butler1*, Yi Tseng1, Cheng-Rong Hsing2, Yu-Mi Wu1, Raman Sankar3,4, Mei-Fang Wang1, Ching-Ming Wei2, Fang-Cheng Chou4,5,6, Minn-Tsong Lin1,2,7
1Department of Physics, National Taiwan University, Taipei, Taiwan
2Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
3Institute of Physics, Academia Sinica, Taipei, Taiwan
4Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan
5Taiwan Light Source, National Synchrotron Radiation Research Center, Hsinchu, Taiwan
6Taiwan Consortium of Emergent Crystalline Materials, Ministry of Science and Technology, Taipei, Taiwan
7Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan
* Presenter:Christopher J. Butler
Dirac semimetals such as Cd3As2 are a recently discovered class of materials which host three-dimensional linear dispersion around point-like band crossings in the bulk Brillouin zone, and hence represent three-dimensional analogues of graphene. This peculiar electronic phase is enabled by specific crystal symmetries: In the case of Cd3As2, a C4 rotational symmetry associated with its unique corkscrew arrangement of systematic Cd vacancies. Although this arrangement underpins the current crystallographic understanding of Cd3As2, and its theoretical implications, it is strangely absent in microscopic investigations reported previously [1,2]. Here we use a combined approach of first-principles calculations and scanning tunneling microscopy (STM) measurements. We show that the currently held crystallographic model of Cd3As2 is indeed predictive of a periodic zig-zag surface superstructure, which we successfully observe in STM experiments [3,4]. This reconciles the current state of microscopic surface observations with the prevailing crystallographic and theoretical models.

1. S. Jeon, B. B. Zhou, A. Gyenis, B. E. Feldman, I. Kimchi, A. C. Potter, Q. D. Gibson, R. J. Cava, A. Vishwanath, and A. Yazdani, Nat. Mater. 13, 851 (2014).

2. M. N. Ali, Q. Gibson, S. Jeon, B. B. Zhou, A. Yazdani, and R. J. Cava, Inorg. Chem. 53, 4062 (2014).

3. R. Sankar, M. Neupane, S.-Y. Xu, C. J. Butler, I. Zeljkovic, I. Panneer Muthuselvam, F.-T. Huang, S.-T. Guo, S. K. Karna, M.-W. Chu, W.-L. Lee, M.-T. Lin, R. Jayavel, V. Madhavan, M. Z. Hasan, and F.-C. Chou, Sci. Rep. 5, 12966 (2015).

4. C. J. Butler, Y. Tseng, C.-R. Hsing, Y.-M. Wu, R. Sankar, M.-F. Wang, C.-M. Wei, F.-C. Chou and M.-T. Lin, Phys. Rev. B 95, 081410 (2017).

This work was supported in part by the Ministry of Science and Technology and National Science Council of Taiwan through the following Grants: No. MOST 104-2119-M-002-029 and No. NSC 101-2119-M-002-007.

Keywords: Dirac semimetal, crystal symmetry, symmetry-protected topological phase, scanning tunneling microscopy