Experimental evidence for direct insulator-quantum Hall transition in multi-layer graphene

Abstract

We have performed magnetotransport measurements on a multi-layer graphene flake. At the crossing magnetic field Bc, an approximately temperature-independent point in the measured longitudinal resistivity ρxx, which is ascribed to the direct insulator-quantum Hall (I-QH) transition, is observed. By analyzing the amplitudes of the magnetoresistivity oscillations, we are able to measure the quantum mobility μq of our device. It is found that at the direct I-QH transition, μqBc ≈ 0.37 which is considerably smaller than 1. In contrast, at Bc, ρxx is close to the Hall resistivity ρxy, i.e., the classical mobility μBc is ≈ 1. Therefore, our results suggest that different mobilities need to be introduced for the direct I-QH transition observed in multi-layered graphene. Combined with existing experimental results obtained in various material systems, our data obtained on graphene suggest that the direct I-QH transition is a universal effect in 2D.

Dirac fermion heating, current scaling, and direct insulator-quantum Hall transition in multilayer epitaxial graphene

“…This result is further supported by the vastly different I dependences for both sides of the I-QH transition. Our new experimental results, together with recent experimental results [19,20], indicate that direct I-QH transition is a universal effect in graphene. We suggest that further experimental and theoretical studies are required to obtain a complete picture for direct I-QH transition in graphene-based devices.…”

“…Interestingly, a current-independent point in ρ xx is observed. The observed fixed point is reminiscent of the I-QH transition in graphene [19,20]. In order to confirm this interpretation, as shown in Figure 6, we perform magnetoresistivity measurements ρ xx ( B ) at various temperatures in the low current limit to ensure thermal equilibrium between phonons and Dirac fermions.…”

“…Especially, a direct transition from an insulator to a high Landau level filling factor ν ≥ 3 QH state which is normally described as the direct I-QH transition continues to attract interest [16-18]. Very recently, experimental evidence for direct I-QH transition in epitaxial monolayer graphene [19] and in mechanically exfoliated multilayer graphene [20] has been reported. In order to further study direct I-QH transition in the graphene-based system, one may wish to investigate Dirac fermion heating in graphene.…”

Hot Carriers in CVD-Grown Graphene Device with a Top h-BN Layer

“…The conductance fluctuations are observed, and they decrease as L increase from L = 0.32 to 50 K, which are typical properties in disordered mesoscopic graphene [24][25][26][27]. at various driving currents from I = 20 nA to 30000 nA at a fixed L of 0.32 K, which reveals similar conductance fluctuation characteristics by current heating in the nonequilibrium regime due to the hot carrier effects in disordered two-dimensional systems [18,[28][29][30][31].…”

“…In order to further discuss the linear relation between e and that indicates little carrier-phonon scattering in our sample A, we fabricate multilayer exfoliated graphene (sample B) that showed the same linear relation between e and by zero field resistance as a thermometer and conductance fluctuations due to its disordered property as in our previous reports [23][24][25][26]. Again, we are able to measure the conductance fluctuations for temperature and current dependence as shown in Figure 5(a) and inset [13].…”