Abstract

Two-dimensional (2D) materials [1] such as graphene, MoS2, MoSe2, WSe2, etc. have been attracting much interest because of their fundamental importance as well as their potential device applications. In this talk I will concentrate on disordered 2D materials in which interesting physical phenomena can be observed. I shall describe charge transport in a monolayer MoS2 flake over a wide range of carrier density, temperature and electric bias. We find that the transport is best described by a percolating picture in which the disorder breaks translational invariance, breaking the MoS2 system up into a series of electron puddles, rather than previous pictures in which the disorder is treated as uniform and homogeneous. Our work provides useful insight to a unified picture of charge transport in monolayer MoS2 nanoflakes. If time permits, I shall describe strongly insulating behaviour observed in monolayer epitaxial graphene grown on SiC, floating-up the extended states at low magnetic fields in graphene, and its relevance to the direct insulator-quantum Hall transition in two dimensions [2]. This work was done in collaboration with C. Chuang. R. E. Elmquist, A. R. Hamilton, L.-I. Huang, O. Klochan, C.-H. Liu, S.-T. Lo, W. H. Wang, and Y. Yang. I would like to acknowledge financial support from the Ministry of Science and Technology (MOST), Taiwan (grant numbers: MOST 102 -2119-M-002-016-MY3 and MOST 103 -2918-I-002-028) and National Taiwan University (grant numbers: 102R7863, 103R7552-2 and 104R7552-2, and 105R203302).

[1] V. I. Fal’ko, 2D Mater. 1, 010201 (2014). [2] C.-T. Liang and S.-T. Lo, Chin. J. Phys. 52, 1175 (2014).