Interference effects in electronic transport through metallic single-wall carbon nanotubes

In a recent paper Liang {\it et al.} [Nature {\bf 411}, 665 (2001)] showed experimentally, that metallic nanotubes, strongly coupled to external electrodes, may act as coherent molecular waveguides for electronic transport. The experimental results were supported by theoretical analysis based on the scattering matrix approach. In this paper we analyze theoretically this problem using a real-space approach, which makes it possible to control quality of interface contacts. Electronic structure of the nanotube is taken into account within the tight-binding model. External electrodes and the central part (sample) are assumed to be made of carbon nanotubes, while the contacts between electrodes and the sample are modeled by appropriate on-site (diagonal) and hopping (off-diagonal) parameters. Conductance is calculated by the Green function technique combined with the Landauer formalism. In the plots displaying conductance {\it vs.} bias and gate voltages, we have found typical diamond structure patterns, similar to those observed experimentally. In certain cases, however, we have found new features in the patterns, like a double-diamond sub-structure.Comment: 15 pages, 4 figures. To apear in Phys. Rev.

Transport of interacting electrons through a double barrier in quantum wires

We generalize the fermionic renormalization group method to describe analytically transport through a double barrier structure in a one-dimensional system. Focusing on the case of weakly interacting electrons, we investigate thoroughly the dependence of the conductance on the strength and the shape of the double barrier for arbitrary temperature T. Our approach allows us to systematically analyze the contributions to renormalized scattering amplitudes from different characteristic scales absent in the case of a single impurity, without restricting the consideration to the model of a single resonant level. Both a sequential resonant tunneling for high T and a resonant transmission for T smaller than the resonance width are studied within the unified treatment of transport through strong barriers. For weak barriers, we show that two different regimes are possible. Moderately weak impurities may get strong due to a renormalization by interacting electrons, so that transport is described in terms of theory for initially strong barriers. The renormalization of very weak impurities does not yield any peak in the transmission probability; however, remarkably, the interaction gives rise to a sharp peak in the conductance, provided asymmetry is not too high.Comment: 18 pages, 8 figures; figures added, references updated, extended discussio

Carbon nanotube junctions and devices

In this thesis Postma presents transport experiments performed on individual single-wall carbon nanotubes. Carbon nanotubes are molecules entirely made of carbon atoms. The electronic properties are determined by the exact symmetry of the nanotube lattice, resulting in either metallic or semiconducting behaviour. Due to their small diameter, electronic motion is directed in the length direction of the nanotube, making them ideal systems to study e.g. one-dimensional transport phenomena. First, we present mK-temperature current-voltage characteristics of an individual single-wall carbon nanotube showing Coulomb blockade and resonant tunnelling through individual molecular levels. We then report electrical transport measurements on carbon nanotubes with naturally occurring intramolecular junctions. We find that a metal-semiconductor junction behaves like a rectifying diode, whereas the conductance of a metal-metal junction behaves like a tunnel junction with associated power-law dependencies described by a Luttinger liquid model for tunnelling between the two nanotube segments. In order to further study carbon nanotube intramolecular junctions, we developed an atomic force microscope (AFM) manipulation technique, by means of which carbon nanotube junctions such as buckles and crossings are created. The electronic transport properties of these manipulated structures show that they form electronic nanometer-size tunnel junctions. Thereafter, room-temperature single-electron transistors are realized within metallic carbon nanotubes. The devices feature a short (down to 20 nm) nanotube section that is created by AFM manipulation. Coulomb charging is observed at room temperature. We observe unconventional power-law dependencies in the transport properties for which we develop a resonant-tunnelling Luttinger-liquid model. Finally, the low-frequency electronic noise properties of metallic carbon nanotubes are investigated. The noise power exhibits a 1/f frequency dependence that is three orders of magnitude smaller at 8 K than at 300 K. As a demonstration of how these noise properties affect nanotube devices, we present a preliminary investigation of the noise characteristics of an intramolecular carbon nanotube single-electron transistor.Applied Science

Electrical transport through carbon nanotube junctions created by mechanical manipulation

Using an atomic force microscope we have created nanotube junctions such as buckles and crossings within individual single-wall metallic carbon nanotubes connected to metallic electrodes. The electronic transport properties of these manipulated structures show that they form electronic tunnel junctions. The conductance shows power-law behavior as a function of bias voltage and temperature, which can be well modeled by a Luttinger liquid model for tunneling between two nanotube segments separated by the manipulated junction.Comment: 4 pages, 3 figures. To appear in Phys. Rev. B., rapid comm, 200