In particular, single-wall carbon nanotubes (SWCNTs) are interesting because they become metallic and semiconducting, depending on how they are rolled up from the graphene sheet, and they could be applied to various devices such as ultrasmall field-effect transistors, single-electron devices, quantum computing devices, and light-emitting devices. A research group at the Japanese Institute of Physical and Chemical Research (RIKEN) has made extensive experimental efforts to apply SWCNTs to single-electron devices and quantum computing devices (spin qubit) with a single quantum dot as a basic structure.
A single electron transistor (SET) is a device in which a quantum dot (QD) is connected with source and drain contacts through small tunnel junctions. A QD is a small metallic island in which electrons are confined. Therefore, it is sometimes compared with a natural atom, where electrons are confined in the Coulomb potential in a much smaller scale. When the discrete levels and the shell structure are clearly formed, the quantum dot is called an artificial atom. In the SWCNT QD, electrons are confined in a length direction as well as a circumference direction.
The researchers at RIKEN demonstrated the artificial-atom nature of the SWCNT QD, with observations of shell structures and the Zeeman splitting of the single particle states.
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By Michael Berger, Copyright 2006 Nanowerk LLC.