Epitaxial growth and characterization of topological semimetals from the 2D transition metal dichalcogenides family

Prototypical topological Weyl and Dirac semimetals are 3D crystal structures and are typically grown in the form of bulk. Discovering and engineering topological semimetals from the family of 2D TMDs could open the way for exploitation of their topological properties by fabricating thin epitaxial films and devices on suitable substrates. In this work, we show that using molecular beam epitaxy, single and few layers of HfTe₂^[1] and ZrTe₂^[2] can be grown epitaxially on AlN and InAs substrates. By combining ARPES and DFT calculations we provide evidence that they are type-I and type-II Dirac semimetals, respectively, with the Dirac point located at the Fermi energy. Dirac cones are maintained down to the single-layer, suggesting that they could be considered as the electronic analogues of graphene. Moreover, we report the first direct observation at room temperature of the orthorhombic Weyl semimetal phase of MoTe₂^[3]. DFT calculations predict eight type-II Weyl nodes which are located just below the Fermi level, making them accessible to electronic transport, thus creating prospect for practical applications.
[1] S. A. Giamini et al., 2D Mater. 4, 015001 (2017).
[2] P. Tsipas et al., ACS Nano 12, 1696 (2018).
[3] P. Tsipas et al., Adv. Funct. Mater. 28, 1802084 (2018).