Electron transport in carbon nanotube and graphene

This thesis is devoted to study the superconductivity of Carbon Nanotubes (CNTs). Electron transport measurements of high quality 0.4nm CNTs array clearly show a superconducting transition at 15K. Below the transition temperature, CNTs form a 2D array of Josephson junctions as a result of proximity-enhanced coupling between each other, which is verified through the magneto-resistance measurements. The transport of the array is governed by the motion of vortex generated from the thermal instability. The temperature dependence of array’s differential resistance shows the system is possibly approaching to Kosterlitz-Thouless(KT) transition as the temperature goes down. 0.4nm CNTs array provides us a unique system to study the collective excitation of strong-correlated fluctuating condensate of Cooper pairs. Then we ask the question what’s the pairing mechanism in 0.4nm CNTs. This is the single most important issue to understand a novel superconductor. We propose that the symmetry breaking at the edge of CNTs with certain diameter and chirality, will enhance the electron-pairing potential. Then the ballistic transport of Cooper pairs through high quality CNTs will build the phase coherence of the whole systems and drive the CNTs to be superconducting. To test our model, we study the high quality Double Walled Carbon Nanotubes (DWNTs) with inner tube as small as 0.68nm with chirality of (5,5). First, intrinsic superconductivity of DWNTs with normal leads is observed. Second, DWNTs with superconducting leads show higher transition temperature and sharper transition curve. It can not be explained by proximity effects because the channel length is much larger than the coherence length of leads. It is more likely that superconducting leads help proliferation of Cooper pairs on the edge of inner tubes. This strongly supports our model of Curvature-enhanced Edge Pairing Superconductivity (CEPS). Finally, we want to see whether edge state itself is sufficient to drive CNTs to superconductivity. To eliminate the effects of curvature, we conduct experiments on graphene. Ultra-thin graphene with specific edge is needed. For initial results, we fabricate large pieces of graphene and study the gate voltage dependence. What’s most promising is that we successfully pattern sub-20nm features on graphene by Atomic Force Microscope(AFM) nanolithography. It opens a new area of studying edge states of graphene