Jiangxiazi Lin, Ning Wang, Hong Kong University of Science and Technology and Benjamin Piot, LNCMI-Grenoble. 

Semiconducting two-dimensional transition-metal dichalcogenides (TMDCs) have been a recent hot research topic in physics, for their novel optical/electronic properties and potential applications. While phenomena such as direct-to-indirect band-gap transition, spin-orbit coupling, and symmetry-controlled valleytronics have attracted wide studies, investigations on interaction effects in TMDCs are scarce. Our recent work focuses on the K-valley electrons in spin-orbit coupled MoS2 , with inversion symmetry broken by a back-gate voltage. We fabricated hBN-encapsulated bilayer MoS2 devices of outstanding quality, showing a high electron mobility of 24000 cm2 / (V∙s) at 1.2 K and quantized Hall resistance plateaus in high magnetic fields. Shubnikov-de Haas (SdH) oscillations were observed down to a filling factor ν (the number of occupied Landau level) of ν = 2. In the density-field mapping of the SdH oscillations (Figure 1a), Landaulevel (LL) crossings were observed at different carrier densities, and can be explained by a density-dependent interaction-enhanced effective g-factor g*. The giant g* gives a large Zeeman-to-cyclotron energy ratio Ez/Ec which leads to a spin-polarized transport regime. From the filling factor sequence in the mapping, we determined the dependence of g* on carrier density n (Figure 1b). In higher magnetic fields, anticrossings were found near integer ratios of Ez/Ec where the LLs of opposite spins come close in energy (Figure 2). This may indicate a strongly interacting quantum Hall ferromagnetic behavior. Both the density-dependent g-factor and the LL anticrossings point to a strong electron-electron interaction scenario in MoS2.

Figure 1: (a) Density-field mapping of the SdH oscillations. Filling factors are marked along the right and top edges. Red and blue lines mark one pair of spin-up and -down LLs. Crossings (orange oval) between LLs of opposite spins are due to the densitydependent Ez/Ec ratio. The white dashed line marks the upper boundary of the low-lying polarized LLs. (b) Density-dependent interaction-enhanced spin susceptibility extracted from (a).

Figure 2: Waterfall plot of SdH oscillations at different density n near integer Ez/Ec. An obvious anticrossing gap at ν = 7 is marked by the orange oval.

Probing Landau levels of strongly interacting massive Dirac electrons in layer-polarized MoS2, J. Lin, T. Han, B. A. Piot, Z. Wu, S. Xu, G. Long, L. An, P. K. M. Cheung, P-P. Zheng, P. Plochocka, D. K. Maude, F. Zhang, and N. Wang, arXiv:1803.08007 (2018). Under review