Absence of Metal-Insulator-Transition and Coherent Interlayer Transport in oriented graphit.pdf

a r X i v : c o n d - m a t / 0 2 0 6 5 6 5 v 2 [ c o n d - m a t .s t r - e l ] 1 0 O c t 2 0 0 2 Absence of Metal-Insulator-Transition and Coherent Interlayer Transport in oriented graphite in parallel magnetic fields H. Kempa a H. C. Semmelhack a P. Esquinazi a Y. Kopelevich b aDepartment of Superconductivity and Magnetism, Institute for Experimental Physics II, University of Leipzig, Linne?str. 5, D-04103 Leipzig, Germany bInstituto de Fi?sica, Universidade Estadual de Campinas, Unicamp 13083-970, Campinas, Sa?o Paulo, Brasil Abstract Measurements of the magnetoresistivity of graphite with a high degree of control of the angle between the sample and magnetic field indicate that the metal-insulator transition (MIT), shown to be induced by a magnetic field applied perpendicular to the layers, does not appear in parallel field orientation. Furthermore, we show that interlayer transport is coherent in less ordered samples and high magnetic fields, whereas appears to be incoherent in less disordered samples. Our results demonstrate the two-dimensionality of the electron system in ideal graphite samples. Key words: A. Graphite; D. Phase transitions; D. Resistivity PACS: 72.20.My, 71.27.+a, 71.30.+k Recent experimental and theoretical studies of graphite have renewed the in- terest in this system [1,2,3,4,5,6,7,8,9,10]. Experimental results show that, con- trary to the common belief, the transport and magnetic properties of graphite cannot be accounted for by semiclassical models. Experiment and theory raise a number of questions concerning the coupling between the graphite layers. The understanding of the transport properties is of primary interest and can provide a fundamental contribution to the physics of two-dimensional (2D) systems in general. In this letter we deal with two important open questions: 1. A MIT appears both in the in-plane [1,3,4] and out-of-plane [5] resistivity induced by a magnetic field B applied perpendicular to the graphite layers, i.