Superconductors Have Niche Present And Immense Potential Uses
Superconductivity is a phenomenon characterised by exactly zero resistivity and complete expulsion of magnetic field from the interior of superconductors. This happens abruptly when the temperature is lowered bellow critical temperature (Tc) characteristic of the material with some conditions on current and magnetic field. Many metals and metalloids exhibit superconductivity especially under high pressure but Tc is not higher than 20,000. These are referred to as Type I superconductors.
Type II superconductors
Later many metallic compounds and alloys were found to exhibit superconductivity but with gradual transition and are called Type II superconductors. Here there are 2 limits of magnetic field between which expulsion of magnetic field or Meissner effect is only partial. As the applied magnetic field is increased beyond the second limit, the superconductivity is destroyed.
The high Tc of these superconductors increases their commercial use. In 1986 a Lanthanum-based cuprate perovskite (where metal to Oxygen ration is about 2:3) material was discovered with Tc around 30K. Later substituting Yttrium for Lanthanum increased Tc to 92K. Then Mercury copper-oxides (HgBa2Ca2Cu3O8) took the limit to 138K. Iron based compounds called pnictides also hold promise though Tcs are around 50K. H2S under extreme pressure has Tc of 203K. A new series of compounds e.g. Sn12SbTe11Ba2V2Mg24O50+ have shown Tc above 450K in lab.
Explanation
Superconductivity cannot be explained by extrapolating classical theory of electricity and is a Quantum Mechanical phenomenon. BCS theory explains superconductivity for Type I superconductors by using the concepts of Cooper pairing of electrons whereby the pair moves in the lattice without inducing lattice vibrations and hence no dissipation of energy.
But there is no consensus on explanation of high Tcs of Type II superconductors. In fact many of them are based on ceramics which are insulators. It could be that planar weight ratios or high dielectric constant of the constituents or the holes of Oxygen are responsible for this
Current Applications
The zero resistivity of superconductors implies little energy loss when even when large currents are passed through them. This is used to create very strong magnets as magnetic field produced by wires is directly proportional to the current. These magnets are used for bending particles in particle accelerators e.g. LHC (Large Hadron Collider) uses magnets that produce field of a few Teslas. The most ambitious project for Nuclear Fusion, ITER (International Thermonuclear Experimental Reactor) uses the superconductors for creating roughly the same size of magnetic field.
One important non invasive body probing technique, MRI (Magnetic Resonance Imaging) uses magnetic fields generated by superconductors to interact with Hydrogen atoms and fat molecules in the body and creates images based on the reaction.
Superconductors are used to build Josephson junctions which uses 2 superconductors which sandwich an insulator in between. Josephson junctions are used to create SQUIDs (Superconducting Quantum Interference Devices) which are very sensitive in detecting magnetic fields. They are used for detecting and removing mines. SQUIDs are also used in a technique called Magnetoencephalography to probe human body which is better than MRI.
Maglev trains (Magnetic Levitation) run with the help of magnets. They are the fastest trains and in test runs, a Japanese train has attained the speed of 603 KM/Hr. They do not use wheels when levitating and hence need less maintenance and more significantly there is no friction at tracks. They have smoother rides and produce less human discomfort. Electrodynamic Suspension (EDS) which uses superconducting magnets is used for the fastest Maglevs. Emerging technologies e.g. Hyperloop also need leviathan and may use superconducting magnets.
The continuous rise of Tc of Type II semiconductors holds immense commercial potential.
Potential Applications
Electrical
As per World Bank, globally electric power transmission and distribution losses are above 8%. This can be dramatically reduced by using superconducting wires which will also be less bulky than the currently used copper wires. This requires Tc to rise as currently cost of cooling outweighs the benefits. Also the superconductors must be ductile so that they can be easily drawn into wires. Niobium-titanium is a promising material for this.
Superconductors can improve efficiencies of electric generators to above 99% and reduce their size. Similar benefits can happen for superconductor based transformers, motors and current limiters. In power generation, high-temperature superconductors can help reduce CO2 emissions.
Computers
Superconductors can help in improving the speed of computers as improvement in performance of microprocessors face technical challenges. Quantum computers are now entering commercial use and may eventually run faster than classical computers. IBM and Google are building qubits (equivalent to bits in classical computers) out of superconducting materials. Rapid single flux quantum (RSFQ) are devices that store information as quanta of magnetic flux and are based on superconducting devices, Josephson junctions. Their operating frequency could be in hundreds of GHz which is order of magnitude times more than that of CMOS based transistors and they also consume less power which is a massive challenge to increase the speed of CMOS based transistors.
Communication
Electronic filters that are used for selecting certain frequencies over other in received signals. However the electrical resistance of the circuitry reduces their efficiency. Superconductors can improve such filters provided their resistance remains zero or low at high frequencies. The routers used in internet further need to improve as data transmissions explodes. One company Irvine Sensors Corp plans to make superconductor based routers with speed as much as 740 Gbit/s which order of magnitude times faster than current routers.
Future
The critical temperatures of superconductors are rising and different families of superconducting materials are being discovered. This helps reduce cost of existing applications and increases their spread. For example General Electric has estimated the potential worldwide market for superconducting generators in the next few years at around $20-30 billion dollars. This coupled with technological challenges in advancement of transistors, mode of transports, communication etc are fuelling the growth of superconductivity. Surprising this is happening even as scientists struggle to explain the phenomenon from theoretical perspective, a rare case of implementation running ahead of theory.
