Metal-insulator crossover in monolayer MoS 2

I Castillo (1) , T Sohier (1, 2) , M Paillet (1) , D Cakiroglu (1, 3) , C Consejo (1) , C Wen (4) , F Wasem Klein (1) , M.-Q Zhao (5, 6) , A Ouerghi (7) , S Contreras (1) , A T Charlie Johnson (6) , M J Verstraete (2) , Benoit Jouault (1) , S Nanot (1)

1 L2C - Laboratoire Charles Coulomb
2 Q MAT CESAM, Univ Liege, Theoret Mat Phys, Liège
3 Aalto University
4 University of Pensylvania
5 NJIT - New Jersey Institute of Technology [Newark]
6 Department of Physics and Astronomy, University of Pennsylvania
7 C2N - Centre de Nanosciences et de Nanotechnologies

We report on transport measurements in monolayer MoS2 devices, close to the bottom of the conduction band edge. These devices were annealed in situ before electrical measurements. This allows us to obtain good ohmic contacts at low temperatures, and to measure precisely the conductivity and mobility via four-probe measurements. The measured effective mobility up to μ eff = 180 cm 2 V −1 s −1 is among the largest obtained in CVD-grown MoS2 monolayer devices. These measurements show that electronic transport is of the insulating type for σ ≤ 1.4 e 2 / h and n ≤ 1.7 × 10 12 cm −2 , and a crossover to a metallic regime is observed above those values. In the insulating regime, thermally activated transport dominates at high temperature ( T > 120 K). At lower temperatures, conductivity is driven by Efros–Schklovkii variable range hopping in all measured devices, with a universal and constant hopping prefactor, that is a clear indication that hopping is not phonon-mediated. At higher carrier density, and high temperature, the conductivity is well modeled by the Boltzmann equation for a non-interacting Fermi gas, taking into account both phonon and impurity scatterings. Finally, even if this apparent metal-insulator transition can be explained by phonon-related phenomena at high temperature, the possibility of a genuine 2D MIT cannot be ruled out, as we can observe a clear power-law diverging localization length close to the transition, and a one-parameter scaling can be realized.

Mots clés: MoS2; transition metal dichalcogenides; electronic transport; metal insulator transition

Domaines: Systèmes mésoscopiques et effet Hall quantique [cond-mat.mes-hall]

I Castillo, T Sohier, M Paillet, D Cakiroglu, C Consejo, et al.. Metal-insulator crossover in monolayer MoS 2. Nanotechnology, 2023, 34 (33), pp.335202. ⟨10.1088/1361-6528/acd3f7⟩. ⟨hal-04144576⟩