1. SUPERCONDUCTIVITYSubmitted By :Hemanshi Kalra

2. What is superconductivity? Superconductivity is a phenomenon of exactlyzero electrical resistance and expulsionof magnetic fields occurring incertain materials when cooled below acharacteristic critical temperature.It was discovered by Dutchphysicist Heike KamerlinghOnnes on April 8,1911 inLeiden. 3. Meissner Effect When a material makes thetransition from the normalto superconducting state, itactively excludes magneticfields from its interior. It was discovered by Germanphysicists WaltherMeissner and RobertOchsenfeld . 4. A magnet levitating above a superconductor cooledby liquid nitrogen. 5. The BCS TheoryElectron-Lattice Interactions A passing electron attracts the lattice, causing a slight ripple toward its path. Another electron passing in the opposite direction is attracted to thatdisplacement.BCS theory suggests that superconductors have zero electrical resistancebelow critical temperatures because at such temperatures the electrons passunhindered through the crystal lattice and therefore lose energy. The theorystates that the supercurrent in a superconductor is carried by many millionbound electron pairs, called Cooper Pairs. 6. High TC Super conductors.In a super conductor if the transition temperature is high ie.,greaterthan 20K, then it is called as high-temperature super conductors.In 1986, Muller and Bednorz discovered high tempertaure superconductor in Ceramics. 7. Superconducting Materials 8. Metal and Alloys Some metals become superconductorsat extremely low temperatures Some of these include mercury, lead, tin,aluminum, lead, niobium, cadmium,gallium, zinc, and zirconium Unfortunately, the critical temperaturesare too low for practical application Metal alloys like Nb-Ti, and Nb-Zr areusually Type II superconductors Metal Alloys have higher criticaltemperatures and magnetic fluxes thanpure metals. As a consequence of their properties,they are more useful for practicalapplications than pure metals 9. Iron Based Superconductors Iron-based superconductors containlayers of iron and a pnictide such asarsenic or phosphorus .This iscurrently the family with the secondhighest critical temperature, behindthe cuprates. The crystalline material, knownchemically as LaOFeAs, stacks ironand arsenic layers, where theelectrons flow, between planesof lanthanum and oxygen.Crystal structure of LaFeAsO, one ofthe ferropnictide compounds 10. Cuprates Cuprate superconductors aregenerally considered to be two-dimensionalmaterials with theirsuperconducting propertiesdetermined by electrons movingwithin weakly coupled copper-oxide(CuO2) layers. Neighboring layerscontaining ions suchas lanthanum, barium, strontium, orother atoms act to stabilize thestructure and dope electrons or holesonto the copper-oxide layers. Cuprates Superconducting materials.HgBa2Ca2Cu3Ox (critical temperature to 133 K)Bi2Sr2Ca2Cu3O10(BSCCO) (critical temperature to 110 K)YBa2Cu3O7 (YBCO) (critical temperature to 92 K.) 11. Organic Superconductors Superconductivity in low dimensional organic materials was first suggested byLittle in 1965. C60 by itself is a very poor conductor. By doping this compound with electrondonors such as alkaline metals, which provide the conduction electrons,superconductivity can be induced. K3C60 has a Tc of 19 K Other superconductors in which conductivity arises inthe pi-electrons of unsaturated bonds have also beendiscovered. Scientists have created the first organicsuperconductor based on a simple aromatic molecule,picene (C22H14), doped with an alkali metal.Dependingon the potassium content, the materials Tc varies from7 to 18K. 12. Applications Superconducting levitation:Maglev Trains (On Track with superconductivity) 13. Medical Diagnosis 14. Power CablesSuperconducting wires carry up to five times thecurrent carried by copper wires with the samecross section.Superconducting cables are cooled to removethe resistance to the flow of electricity, cuttingdown on the losses that typically occur duringtransmission.CommunicationsHTS filters will enhance signal-to noiseratios in cellular communications systemsleading to reliable communication serviceswith fewer spaced cell towers. 15. Limitations For presently known practical superconductors, the temperature is muchbelow 77 Kelvin, the temperature of liquid nitrogen. Keeping them belowthat temperature involves a lot of expensive cryogenic technology. Scientists are working on designing superconductors that can operate atroom temperature. Type II superconductors in particular are extremely brittle, limiting theirrange of practical applications. Although Type I superconductors generallyare not as brittle. The other major limitation of superconductors is their sensitivity tochanging magnetic fields, meaning that AC current will not work effectivelywith superconductors.