ISSN 1998-0124 CN 11-5974/O4 2019, 12(1): 000–000 https://doi.org/10.1007/s12274-020-2892-8 Research Article Quasiparticle interference and impurity resonances on WTe 2 Hyeokshin Kwon 1,§ , Taehwan Jeong 2,§ , Samudrala Appalakondaiah 2,3,§ , Youngtek Oh 1 , Insu Jeon 1 , Hongki Min 4 , Seongjun Park 1 (  ), Young Jae Song 2,3,5,6 (  ), Euyheon Hwang 2,3 (  ), and Sungwoo Hwang 1 1 Samsung Advanced Institute of Technology, Samsung Electronics Co., Suwon 16678, Republic of Korea 2 SKKU Advanced Institute of Nano Technology (SAINT), Sungkyunkwan University, Suwon 16419, Republic of Korea 3 Department of Nano Engineering, Sungkyunkwan University, Suwon 16419, Republic of Korea 4 Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea 5 Department of Physics, Sungkyunkwan University, Suwon 16419, Republic of Korea 6 Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science (IBS), Sungkyunkwan University, Suwon 16419, Republic of Korea § Hyeokshin Kwon, Taehwan Jeong, and Samudrala Appalakondaiah contributed equally to this work. © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 26 September 2019 / Revised: 14 May 2020 / Accepted: 21 May 2020 ABSTRACT Using scanning tunneling microscopy/spectroscopy (STM/STS), we examine quasiparticle scattering and interference properties at the surface of WTe 2 . WTe 2 , layered transition metal dichalcogenide, is predicted to be a type-II Weyl semimetal. The Weyl fermion states in WTe 2 emerge as topologically protected touching points of electron and hole pockets, and Fermi arcs connecting them can be visible in the spectral function on the surface. To probe the properties of surface states, we have conducted low-temperature STM/STS (at 2.7 K) on the surfaces of WTe 2 single crystals. We visualize the surface states of WTe 2 with atomic scale resolution. Clear surface states emerging from the bulk electron pocket have been identified and their connection with the bulk electronic states shows good agreement with calculations. We show the interesting double resonance peaks in the local density of states appearing at localized impurities. The low-energy resonant peak occurs near the Weyl point above the Fermi energy and it may be mixed with the surface state of Weyl points, which makes it difficult to observe the topological nature of the Weyl semimetal WTe 2 . KEYWORDS WTe 2 , Weyl semimetal, quasi-particle interference, scanning tunneling microscopy/spectroscopy 1 Introduction Novel topological states of matter have attracted much attention in the past decades. Especially, much recent interest in condensed matter physics has focused on bulk chiral materials with a gapless band structure including three-dimensional (3D) Weyl and Dirac semimetals [1–13], in which the elementary low-energy noninteracting electronic energy dispersion is linear and can be written in terms of Weyl and massless Dirac Hamiltonians, respectively. In 3D Weyl semimetals, due to the topologically protected bulk quasiparticles the topological protected surface states exist. Topological Weyl semimetals (WSMs) are new states of quantum matter and they have been known to exist theoretically. Recently they have been found experimentally in a crystal lattice as low-energy quasiparticle excitations [14–18]. A nonmagnetic semimetal in the TaAs family with time-reversal symmetry and broken space-inversion symmetry was theoretically predicted to be a WSM and subsequent experimental verification has motivated intensive studies on topological semimetals [19–23]. In the Weyl fermion band structure, topologically protected Fermi arcs were predicted to exist on its surface connecting projections of two Weyl points with opposite chirality in the crystal lattice, and these have been confirmed to reside on the surface of TaAs in angle-resolved photoemission spectroscopy (ARPES) [19–21] and scanning tunneling microscopy/spectroscopy (STM/STS) [22, 23] experi- ments. In addition to standard type-I WSMs which have Weyl points with a point-like Fermi surface, type-II WSMs were recently proposed [24]. In type-II WSM the Weyl points emerge at the contact points of the electron and hole pockets. WTe2 is one of the first predicted type-II WSM. WTe2 with its noncentrosymmetric orthorhombic Td phase is a layered transition metal dichalcogenide, and the exotic electronic properties such as the nonsaturating magnetoresistance [25] and pressure-induced superconductivity [26, 27] have been experimentally reported. The existence of surface Fermi arcs is one of the interesting properties of topological WSMs. Thus, to understand the electronic properties of the topological surface states emerging out of the bulk electron-hole pockets the existence of surface states are needed for topological WSMs. Recent ARPES experiments on the type-II WSM WTe2 indicate the existence of surface states, but these states do not clearly manifest a topological nature of type-II Weyl points in the bulk [28–32]. Thus, other experiments are required to probe the topological nature of the type-II WSM WTe2. In this work, we investigate detailed quasiparticle interference (QPI) and perform a scattering analysis on the surface of the type-II WSM WTe2 to examine the surface properties of WTe2. Address correspondence to Seongjun Park, s3.park@samsung.com; Young Jae Song, yjsong@skku.edu; Euyheon Hwang, euyheon@skku.edu