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Success stories

Jeff Tallon: High Temperature Superconductors

Jeff Tallon and the team at IRL (December 2003)

Within the unimposing walls of Industrial Research's Seaview buildings lies the seed of a world wide superconducting trade. Over the past 12 years Jeff Tallon and his team have developed and marketed the world's first high temperature superconductors (HTS's) and are forging ahead into this untamed field of science. After years of legal battles they have finally won the exclusive rights to produce and sell their superconducting materials.

Getting down to business

HTS-110, a new technology business has been set up within IRL to take full advantage of the high temperature superconducting market. One of the labs at IRL (pictured below) forms the centre of research for new technology. Very powerful magnets are being made by winding superconducting tape and insulating tape together into large coils and passing huge currents through them. HTS-110 is also developing applications for specialist motors, generators and power control devices. In a few years inch by inch superconducting plates designed at IRL could be found on cell phone towers all over the country.

Winding the superconducting coils. Jeff looks on.

High Temperature Superconductors

The HTS's we are talking about are called cuprates. They consist of nanometer scale planes of superconducting CuO interspersed with layers of non-superconducting atoms. Properties such as critical temperature (the temperature below which superconductivity exists) and the stability of the superconducting state can be changed by altering the cuprate composition, the thickness of atomic nano-layers, the temperature and pressure at which the materials are fabricated and many other parameters. At IRL all these factors are being explored. A range of high tech specialized machines makes nano-scale investigations possible. There are ion deposition machines (similar to those used to make GaN films)that allow the production of films of nanometer thickness, high pressure systems, vacuums, furnaces, powerful magnets, a transmission electron microscope, spectroscopy machines and a SQUID (Superconducting Quantum Interference Device) the most sensitive magnetic field detector available which is sponsored by the MacDiarmid Institute and can be seen in the left bottom corner of the group photo above..

The cuprate structure

What causes superconductivity?

Although the production and application of HTS's for technology is moving ahead in leaps and bounds, the theory behind them, requiring deep insight into the nano-scale operations within the material is still largely unknown. The defining factor of superconductors is that they exclude all magnetic fields within them. When a superconductor is placed in a magnetic field, tiny nano-scale circulating currents within it create fields, which totally cancel the external field. Unlike perfect diamagnets they do this for DC as well as changing fields. This extraordinary phenomenon is known as the Meissner effect.

The resistance of a superconductor showing the 
transition to zero resistance, in this case at around 90K

The widely accepted BCS theory for superconductivity involves the formation of 'cooper pairs'. These are pairs of electrons with opposite spin bound together by the exchange of phonons (lattice vibration energy quanta). The pair forms together a meson with zero spin, which moves through the positive ion lattice with no resistance. At low temperatures the system remains in a metastable superconducting state however if the temperature exceeds the critical temperature or the current becomes too high superconductivity is lost. This theory appears to work well for low temperature superconductors but it seems an unlikely explanation for the high temperature cuprates. It is unknown why the superconducting state not disturbed by the considerable thermal energy of the lattice at high temperatures?

At IRL they are doing isotopic studies on cuprate superconductors to find the cause of superconductivity. They replace the 16 O in CuO bonds with 17 O or 18 O by pumping gas into a vessel containing the sample. The results are very surprising. The superconducting state is hardly altered by the isotopic changes. Because the process described above involves lattice vibrations, the state should be affected by the mass of the ions (as the frequency of an object on a spring is affected by the object's mass). If this is not so then what is the cause of superconductivity? An unanswered question and a challenge for Jeff and his team!

From left to right: The furnace room, a superconducting magnet and three superconducting pellets straight out of the furnace.

The future

The field of superconductors is full of ambiguities, challenges and vast possibilities. Over the past few years Jeff and his team at IRL have prepared and planted this field. They are now beginning to gather the fruits of their labour. There is still plenty more to learn about high temperature superconductors but the future looks bright and the benefits will be felt by NZ as a whole. A testimony to kiwi ingenuity!