The feasible. The switching device (transistor) proposed by

The
study of the spin of the electron in solid-state devices is known as
spintronics. By manipulating the spin of electrons in a system it is possible
to design switching devices based on this phenomenon. However cascading such
devices in order to design logic gates (which are what computers are based
upon) has long been a major challenge, yet an all-carbon design might be
feasible.

The
switching device (transistor) proposed by the team working in Florida consists
of a graphene nanoribbon (GNR, a thin strips of graphene) created by unzipping
a carbon nanotube (CNT) with 2 parallel CNT wires on either side. There exists
a constant voltage across all of the 3 components.  With current flowing in the CNT a magnetic
field is thus generated. Fig.3 illustrates this.

The
important phenomenon here is the negative magnetoresistance of  the GNR, that is to say its resistivity
decreases with increasing external magnetic field. This results due to spin
interaction in the material with the magnetic field that will not be explained
in detail here. Hence the magnitude of the GNR current acts as the binary
output of the transistor. Specifically binary 1 is represented by the large
current when the CNT magnetic fields are present and binary 0 by the much
smaller current when the magnetic field is not present. The current from the
GNR can now act as the binary input to further gates and thus be used to form
the complex set of logic gates that are used to perform the desired
function.  The exceptionally high
computational ability of computers designed on such transistors (a clock speed
of 2 THz is proposed) is a product of the low switching delay, which are in
turn caused by the low times required to switch the magnetic field on and off.

Now
whilst other materials exhibiting negative magnetoresistance and high
conductivity could be utilised instead of graphene no other material currently
fits the requirements as well as  CNTs
and GNRs. 14