Visualizing Type-II Weyl Points on a Tungsten Ditelluride Surface
Chun-Liang Lin1*, Ryuichi Arafune2, Ro-Ya Liu3, Masato Yoshimura1, Baojie Feng3, Kazuaki Kawahara1, Zeyuan Ni4, Emi Minamitani4, Satoshi Watanabe4, Youguo Shi5, Maki Kawai1, Tai-Chang Chiang6, Iwao Matsuda3, Noriaki Takagi1
1Department of Advanced Materials Science, The University of Tokyo, Chiba, Japan
2International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Ibaraki, Japan
3Institute for Solid State Physics, The University of Tokyo, Chiba, Japan
4Department of Materials Engineering, The University of Tokyo, Tokyo, Japan
5Institute of Physics, Chinese Academy of Sciences, Beijing, China
6Department of Physics, University of Illinois, Illinois, USA
* Presenter:Chun-Liang Lin,
Topology in abstract mathematics has revolutionized our conventional understanding of condensed matter physics, resulting in the emergence of exotic quantum phases such as topological insulators (TIs). Recently the realization of the Weyl semimetals (WSMs) leads us to uncover the topological phases of matter beyond TIs. WSMs have gathered a deal of great attention because the quasiparticles in WSMs behave as Weyl fermions, massless chiral fermions long sought in particle physics. WSMs are classified into two types, type I and II, according to the topology of the Weyl point, where the electron and hole pockets touch each other. Tungsten Ditelluride (WTe2) is a strong candidate of type-II WSM proposed by the theory [1]. Here, we measured energy-dependent quasiparticle interference patterns on a Td phase WTe2 with a cryogenic scanning tunneling microscope, revealing the position of the Weyl point and its connection with the Fermi arc surface states. The results [2] are also in agreement with prior theoretical predictions [3]. Our results provide a conclusive answer to the issue and serve to motivate further exploration of the novel characteristics of WSMs.

[1] Soluyanov, A. A. et al., Nature 527, 495 (2015).
[2] Lin, C. -L. et al., ACS Nano DOI: 10.1021/acsnano.7b06179
[3] Bruno, F. Y. et al., Phys. Rev. B 94, 121112(R) (2016).

Keywords: Weyl semimetals, Fermi arc, quasiparticle interference, transition metal dichalcogenides, scanning tunneling microscopy