|
New
Release -- Superconductor Week does not edit or endorse the following
news release:
Super-carbon: superconductivity and
relativity meet in a monolayer of graphite
28 February 2007: Until recently,
superconductivity and the theory of relativity ‑ two of the last century's
greatest discoveries in physics ‑ had very little to do with each other.
However, researchers at TU Delft's Kavli Institute for Nanoscience and the
FOM Foundation have, for the first time, detected superconducting
properties in a material comprised of massless, relativistic electrons.
Their device - which consists of graphene attached to superconductors - also
functions as a bipolar transistor for superconducting currents. The
researchers will publish this scientific breakthrough on 1 March 2007 in the
journal Nature.
A piece of graphite, with layers of varying thickness, on a silicon
chip. The thinnest sections consist of just one layer. A single
layer of graphite is referred to as graphene. This photo was taken
with an optical microscope and the entire image measures 100 x 75
micrometers.
When you use a pencil to draw a line on a piece of paper, thin layers of
graphite remain on the paper. This works so well, because graphite consists
of stacks of carbon layers, which easily slide over each other. The graphite
remaining on the paper varies in thickness from several thousand layers to
only a few. In 2004, researchers in Manchester (UK) were able to
successfully isolate a single layer of graphite: graphene. Since then, there
has been great interest in this material throughout the world, because of
its special electrical properties. In particularly fascinating is the fact
that the electrons in graphene seem to be massless. These electrons are not,
of course, actually massless. It is their interaction with the atoms in
graphene that makes them behave as if they were. This means that they have
properties that can only be explained by Einstein's theory of relativity.
For instance, the electrons in graphene move at a constant velocity, just as
light does.
Hubert Heersche, Pablo Jarillo-Herrero and their fellow researchers have
attached graphene to a superconductor. In a superconductor, the electrical
resistance completely disappears at very low temperatures. This means that
an electrical current can continue to flow even without a voltage being
applied (physicists call this a supercurrent). When graphene - which itself
has no superconducting properties - is joined together with a
superconductor, it can behave like a superconductor. This effect has been
identified in many other non-superconducting materials and is known as the
Josephson-effect. The TU Delft researchers have now demonstrated that
massless electrons can also carry a supercurrent, and for the first time
they were able to measure the relativistic Josephson effect.
Supercurrent transistor
The researchers have also demonstrated that graphene can serve as a
supercurrent transistor. A transistor is an electrical component in which
the current can be regulated by applying a voltage to the so-called
'gate-electrode'. Heersche and colleagues have created a device in which the
supercurrent can be regulated by a voltage: a supercurrent transistor.
A conventional transistor is made from a semiconductor. Graphene is not a
semiconductor, but rather a semi-metal. This means that not only the size of
the supercurrent can be regulated, but also the type of charge carrier. This
can be electrons (with a negative charge) or holes (with a positive charge).
The TU Delft team is the first to make a bi-polar supercurrent-transistor.
Carbon electronics
The work that has been accepted for publication by Nature is part of
a project in which the TU Delft team investigates the electrical properties
of graphene. Graphene is being studied intensely throughout the world,
because it is believed that graphene can play an important role in the
electronics of the future. Large companies too are interested in carbon
electronics, because in many respects graphene has superior properties
compared to conventional materials, such as silicon. For now, Heersche
expects that graphene will mostly continue to be a fascinating material for
fundamental research. The striking combination of superconductivity and
relativity in graphene constitutes a clear example.
Return
to industry news releases |
|
|
"Superconductor Week
has a three-fold
mission:
to advance the goals of our readers
by a critical
perspective on low- and high- Tc superconductors and cryogenics; to promote the
industry by spreading information and insight to the broadest possible audience;
and to provide
a platform for the free exchange of ideas and news within the
superconductivity community."
-- Mark Bitterman
Executive Editor |
|
|
