In order to further study the observed I-QH transition, we analyze the amplitudes of the magnetoresistivity oscillations versus the inverse of B at various temperatures. As shown in Figure 4, there is a good linear fit to Equation 1 which allows us to estimate the quantum mobility to be around 0.12 m2/V/s. Therefore, near μ q B c ≈ 0.37 which is considerably smaller than 1. Our results obtained on multi-layered graphene Protein Tyrosine Kinase inhibitor are consistent with those obtained in GaAs-based weakly

disordered systems [19, 21]. Figure 4 as a function of the inverse of the magnetic field 1/ B . The solid line corresponds to the best fit to Equation 1. It has been shown that the elementary neutral excitations in graphene in a high magnetic field are different from those of a standard 2D system [51]. In this case, the particular Landau-level quantization in graphene yields linear buy Everolimus magnetoplasmon modes. Moreover, instability of magnetoplasmons can be observed in layered

graphene structures [52]. Therefore, in order to fully understand the observed I-QH transition in our multi-layer graphene sample, magnetoplasmon modes as well as collective phenomena may need to be considered. The spin effect should not be important in our system [53]. At present, it is unclear whether intra- and/or inter-graphene layer interactions play an important role in our system. Nevertheless, the fact that the low-field Hall resistivity is nominally T-independent suggests that Coulomb interactions do not seem to be dominant in our system. Conclusion In conclusion, we have presented magnetoresistivity measurements on a multi-layered graphene flake. An approximately temperature-independent point in ρ xx is ascribed to the direct I-QH transition. Near the crossing field B c, ρ xx is close to ρ xy , indicating that at B c, the classical mobility is close to 1/B c such that B c is close to 1. On the other hand, μ q B c ≈ 0.37 which is much smaller than 1. Therefore, different mobilities must be considered for the direct I-QH transition. Together Reverse transcriptase with existing experimental results obtained on various material systems, our new results obtained in a

graphene-based system strongly suggest that the direct I-QH transition is a universal effect in 2D. Acknowledgments This work was funded by the National Science Council (NSC), Taiwan (grant no: NSC 99-2911-I-002-126 and NSC 101-2811-M-002-096). CC gratefully acknowledges the financial support from Interchange Association, Japan (IAJ) and the NSC, Taiwan for providing a Japan/Taiwan Summer Program student grant. References 1. Novoselov KS, Geim AK, Morozov SV, Jiang D, Zhang Y, Dubonos SV, Grigorieva IV, Firsov AA: Electric field effect in atomically thin carbon films. Science 2004, 306:666.CrossRef 2. Zhang Y, Tan Y-W, Stormer HL, Kim P: Experimental observation of the quantum Hall effect and Berry’s phase in graphene. Nature 2005, 438:201.CrossRef 3.