NATIONAL HIGH MAGNETIC FIELD LABORATORY 2006 RESEARCH REPORT TRANSITION OF GRAPHITE ELECTRONIC STRUCTURE FROM BULK-TO-NANO, STUDIED IN HIGH MAGNETIC FIELDS E. Jobiliong, J.G. Park, R. Vasic, and J.S. Brooks (FSU, Physics) Introduction Thin layers of graphite can be produced by relatively easy cleaving with adhesive tape or other means, and with care, few layer graphite (FLG) sheets of less than 10 layers, and even single layer graphite (graphene) can be obtained[1]. In this report we describe the investigation of few layer graphite samples in the range of 400 to 40 graphene layers[2]. We find that the electronic structure starts to go from a bulk-like to a graphene-like structure at a surprisingly large number of layers. Experimental Samples of few-layer graphite were prepared by cleaving with adhesive tape, and then pressing onto a silicon substrate in a FET configuration. Here the SiO 2 insulating layer was 100 nm thick, and the substrate was doped-metallic and served as the gate. Gold electrodes where formed by e-beam evaporation on the top of the sample using lithographic methods. Results and Discussion For a broad perspective, high field studies of both bulk and FLG systems are shown in Fig. 1. For bulk graphite[3], Shubnikov de Haas (SdH) oscillations are observed which reach the quantum limit by 10 T, and a field induced CDW-type state forms above 25 T. In a 130 nm FLG (corresponding to about 390 single graphene layers), the SdH are still weakly apparent, but the CDW transition is highly suppressed. For the 15 nm FLG (corresponding to about 45 graphene layers) the SdH associated with the bulk material are replaced by a new, electric field dependent oscillation frequency, shown in Fig. 2, and the CDW signature is no longer apparent. (b) (c) 130 nm 15 nm bulk Fig. 1. Magnetotransport in (a) bulk Kish graphite[3]. (b) 130 nm thick FLG. Inset shows the detail of the field dependence between 20 T and 33 T. (c) 15 nm thick FLG. Curves for different gate voltage are offset for clarity. Conclusions Fig. 2. Gate dependence of oscillation frequency from Fig. 1c. Although the gate-dependent oscillation frequency seen in the thinnest sample (Fig. 1c) is consistent with the expected variation of the Fermi level in the “Dirac Cone” picture[1], the high field behavior of the CDW for the thicker sample (Fig. 1b) seems surprising since it is essentially in the bulk limit. At this stage, we are not sure if sample quality, or perhaps the more fundamental implications of the Yoshioka-Fukuyama model for the CDW are responsible for the rapid vanishing of the CDW behavior in the FLG limit. Acknowledgements This work was supported in part by NSF-DMR–0602859 and the NHMFL. References [1] K. S. Novoselov et al., Nature (London) 438, 197 (2005); Y. Zhang, Nature 438, 201 (2005). [2] E. Jobiliong et al., Curr. Appl. Phys. In Press, Available online 2 November 2006. [3] S. Uji, J. S. Brooks, and Y. Iye, Physica B 246-247, 299 (1997). View publication stats View publication stats