Superconductors Essay, Research Paper
What do transportation vehicles, MRIs, electric generators, and
construction sites all have in common? All have either been made possible or
more effective through the use and development of superconductors.
Superconductors are elements in which electrons or electricity can flow
freely and without resistance below a certain temperature. They are the
closest things to perpetual motion in nature for, once set into motion,
current will flow continuously in a closed loop of a superconducting
material. Superconductivity has captivated the minds of scientists and
researchers as one of the last great frontiers of scientific discovery.
Although science is constantly changing and new technological
advancements and discoveries are made daily, still much remains uncertain about
these mysterious materials.
Dutch physicist Heike Kamerlingh Onnes of Leiden University was the
first to observe superconductivity in mercury in 1911 when he cooled the
mercury to four degrees Kelvin, the temperature of liquid mercury, and
the resistance suddenly vanished. Onnes then later won the Nobel Peace
Prize in physics for his research in superconductors in 1913. The next
great discovery did not occur till 1933 when Walter Meissner and Rober
Ochsenfield discovered superconducting materials? ability to repel a
magnetic field. Many naturally occurring substances like water, wood,
and paraffin exhibit weak diamagnetism; however, the superconductors are
able to exhibit strong diamagnetism. A superconductor?s diamagnetism
ability is today called the ?Meissner effect?. Following Meissner and
Ochsenfield?s discovery, many superconducting metals, alloys, compounds,
and their properties were beginning to become revealed.
The first widely accepted theory that deals with superconductors is
BCS Theory. It was developed in 1957 by American physicists John
Bardeen, Leon Cooper, and John Schreiffer, and won them a Nobel Peace prize in
1972. The BCS Theory says that as electrons pass through a crystal,
the structure of the crystal deforms inward and generates sound packets
that they named phonons. The theory goes on to state that these phonons
make the area of deformation positive, which facilitates subsequent
electrons to pass through that area. In 1962, Cambridge University
graduate student Brian D Josephson predicted that electric current would flow
between two superconducting materials, even if they were separated by a
non-superconductor or insulator. His theory was later proven correct
and won him the Nobel Prize in Physics in 1973. His ?tunneling?
discovery is today known as the ?Josephson effect? and become the key to many
electronic devices.
The mysteries of the field of superconductivity began to slowly
unravel during the 1980s. Bill Little of Sandford University suggested the
possibility of organic, carbon-based, superconductors in 1962, but it
was not until 1980 when Danish researcher Klaus Bechgaard of the
University of Copenhagen and three French team members were able to synthesize
the first of these theoretical organic superconductors. Scientific
research slowly continued afterwards until Alex M?ller and Georg Bednorz,
researchers at the IBM Research Laboratory in R?schlikon, Switzerland
made a breakthrough discovery by creating a superconductor out of a
brittle ceramic compound in 1986. They were able to create a
superconductor out of materials that are normally insulators and until that point
had been mostly ruled out by scientists as possible superconducting
candidates. Their discovery won them the Nobel Prize the following year in
1987 and triggered a flood of activity in the field of
superconductivity. In 1997, researches made a discovery that was believed impossible;
they found an alloy of gold and indium at very near absolute zero was
both a superconductor and a natural magnet. In 1999, a similar
discovery was made in a compound of ruthenium and copper. These discoveries
open the doors to endless possibilities in technological advancement, and
at the same time, raise endless questions about the longstanding
theories of superconductivity.
Although not much is currently known about superconductors, there are
three main types of superconductors about which the most is known. One
of these types is Type I Superconductors, also known as soft
superconductors. Another is Type II Superconductors, the hard superconductors,
which also contain the ceramic superconductors. The final type of
superconductors is the atypical superconductors; the atypical
superconductors category includes Fullerenes, which is also known as buckyballs.
Type I superconductors, or soft superconductors, are comprised chiefly
of pure metals that demonstrate conductivity at room temperature as
shown in the periodic table. These superconductors are the ones that have
extremely low critical temperatures. The critical temperature of a
superconductor is the temperature at which it reaches the state of being
superconductive. The critical temperatures of Type I superconductors
range from 0.000325 K, which is quite close to absolute zero, to 17 K.
The critical temperature of 17 K, however, is sulfur when it is put
under a pressure of 1.6 million atmospheres. This is an enormous amount of
pressure and is much too high to allow this superconductor to be useful
to industry. In fact, all of the Type I superconductors have critical
temperatures much too low to be commercially useful superconductors.
Type I superconductors work because the excessively low temperatures
slow down the molecular vibrations enough so that the material is able to
have unimpeded electron flow. BCS theory suggests that in
superconductive materials, the electrons that make up the current flow travel in
pairs called Cooper pairs to overcome obstacles in the crystal, so that
they can both travel faster. One major characteristic of Type I
superconductors is that there is a steep transition from its former state to
its superconducting state. Type I also exhibit diamagnetism. This
means that this type of superconductor repels magnetic fields.