Charge and spin transport in carbon nanotubes

Abstract

The basic science in quantum transport of nano-scaled ‘devices’ is largely based on the availability of suitable model systems. Nanostructures built from conventional metals are typically in the diffusive transport regime. Semiconductors, as the starting material for nanodevices, are different. Because of the low carrier density and therefore reduced screening, the Fermi energy can be tuned by electrostatic gates. Quantum dots which can be filled sequentially with electrons one by one have been realized in this material system (for a review see Kouwenhoven et al (2001 Rep. Prog. Phys. 64 701)). Today, researchers have also started to explore the new possibilities provided by molecules (see, for example, Selzer and Allara (2006 Ann. Rev. Phys. Chem. 57 593), Cuniberti et al (2006 Lecture Notes in Physics vol 680), McCreery (2004 Chem. Mater. 16 4477)). A rather simple prototype ‘molecule’ is a carbon nanotube (CNT) (for recent reviews, see Anantram and Leonard (2006 Rep. Prog. Phys. 69 507), Dresselhaus et al (2001 Topics in Applied Physics vol 80), Ebbesen (1996 Phys. Today 49 26)). Charge and spin transport in CNTs have attracted a lot of attention in recent years. There are several reasons for this excitement: CNTs are almost ideal quantum-ballistic wires. Large electric field effects have been observed in semiconducting CNTs, potentially of interest for applications in electronics. Because a CNT is an all-surface conductor, the electrical properties are highly sensitive to the environment, which can be exploited in sensing applications. Finally, a wealth of new physics is currently appearing in experiments in which CNT-hybrid devices are used, which employ a combination of normal metal, superconducting and ferromagnetic contacts.