Quantum point contact on graphite surface

The conductance through a quantum point contact created by a sharp and hard metal tip on the graphite surface has features which to our knowledge have not been encountered so far in metal contacts or in nanowires. In this paper we first investigate these features which emerge from the strongly directional bonding and electronic structure of graphite, and provide a theoretical understanding for the electronic conduction through quantum point contacts. Our study involves the molecular-dynamics simulations to reveal the variation of interlayer distances and atomic structure at the proximity of the contact that evolves by the tip pressing toward the surface. The effects of the elastic deformation on the electronic structure, state density at the Fermi level, and crystal potential are analyzed by performing self-consistent-field pseudopotential calculations within the local-density approximation. It is found that the metallicity of graphite increases under the uniaxial compressive strain perpendicular to the basal plane. The quantum point contact is modeled by a constriction with a realistic potential. The conductance is calculated by representing the current transporting states in Laue representation, and the variation of conductance with the evolution of contact is explained by taking the characteristic features of graphite into account. It is shown that the sequential puncturing of the layers characterizes the conductance.Comment: LaTeX, 11 pages, 9 figures (included), to be published in Phys. Rev. B, tentatively scheduled for 15 September 1998 (Volume 58, Number 12