Chapter 5
High Temperature Superconductors

Since Heike Kamerlingh Onnes discovered superconductivity, people have been creating superconductors with higher critical temperatures. If there were room temperature superconductors we could replace the conductors in our homes and cities with superconductors, thus saving billions of dollars.

The Beginning of High Temperature Superconductors
High temperature superconductivity began in 1986 when Johannes Georg Bednorz and Karl Alexander Müller in IBM Research Laboratories in Zurich, Switzerland discovered a compound of barium, lanthanum, copper, and oxygen superconductor. The oxide superconductor had a critical temperature of 35K.

Müller had decided to study oxide ceramics to see if they could become superconductive. The idea that ceramics could become superconductive was rather strange considering that ceramics are usually not very good conductors of electricity. Müller was interested in a group of ceramics called pervoskites. This group of ceramics were a compound of oxygen and other metals. Many scientist believed that oxides could not be superconductors. The reason he researched oxide ceramics was because the lab he worked in had researched oxides for quite a while, and scientists at the University of Caen in France had found traces that a ceramic compound of copper, oxygen, lanthanum, and barium had electrical conduction.

It took many years of work and experiments for Bednorz and Müller to find a metallic oxide superconductor. This ceramic superconductor was so odd that they kept their discovery a secret for a while. They published their finding in the September 1986 issue of the German journal Zeitschrift für Physik. It took some time for people to pay attention to the news.

The University of Tokyo in Japan was the first to take Bednorz and Müller’s discovery seriously; they repeated and confirmed the results. Other groups, such as AT&T and Bell Labs, were soon doing the same. They were all in a race to produce a higher temperature superconductor.

The 1-2-3 Superconductor
At the University of Houston in Texas Paul C. W. Chu lead a group to find a higher temperature superconductor than Bednorz and Müller’s superconductor. On February 16, 1987 Paul Chu, supported by the National Science Foundation, created a superconductor with a record high critical temperature of 93K. The compound was made up of oxygen, barium, copper, and yttrium. This was named the 1-2-3 superconductor for its relative atomic proportions of yttrium, barium, and copper.

Chu was curious of what would happen if an oxide superconductor was put under high pressure. He discovered that the higher the pressure, the higher the critical temperature.

In 1988 Paul Chu made a compound of bismuth, strontium, calcium, oxygen, and aluminum which had a critical temperature of 120K.

A group at the University of Arkansas produced a compound of thallium, barium, calcium, copper, and oxygen that had a critical temperature of 125K. Many scientist believe that an entire periodic table will have to be put together to make a room temperature superconductor.

"Superconductivity is perhaps the most remarkable physical property in the universe"
- David Pines, University of Illinois Urbana-Champaign Center for Advanced Study Professor of physics and electrical and computing engineering