Charge Instability in Single-Layer TiTe2 Mediated by van-der-Waals Bonding to Substrates

Meng-Kai Lin^1*, Joseph A. Hlevyack^2,5, Peng Chen³, Ro-Ya Liu², Sung-Kwan Mo⁴, T.-C. Chiang^1,2

¹Physics, National Central University, Taoyuan, Taiwan
²Physics, University of Illinois at Urbana-Champaign, Illinois, USA
³School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China
⁴Advanced Light Source, Lawrence Berkeley National Laboratory, California, USA
⁵Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Illinois, USA

* Presenter:Meng-Kai Lin, email:mklin_ncu@outlook.com

Single layers of transition metal dichalcogenides (TMDCs) are of interest for their emergent properties at the two-dimensional limit. However, the role of substrate effects is rarely discussed. For van-der-Waals bonding to an incommensurate substrate, the interaction can be expected to be weak, but is it negligible? Here, we report an experimental study of a model system to address this issue. The charge instability in a single-layer TiTe2 grown on PtTe2 films is examined as a function of the thickness of PtTe2 films, which are themselves grown on a bilayer-graphene-terminated SiC substrate. The results show that the (2x2) charge density wave in single-layer TiTe2 is strongly suppressed by increasing the film thickness of PtTe2. Given the interfacial bonding remains of the weak incommensurate van-der-Waals type, the observed changes are correlated with a thickness-dependent metallicity transformation in the PtTe2 substrate (from a wide-gap semiconductor to a semimetal). The results illustrate the crucial role of the substrate in single-layer physics.

Keywords: van der Waals, Transition metal dichalcogenide, Band structure, Photoemission, Single layer