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David Liu

on 15 January 2013

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Transcript of Superconductivity

Simply put, superconductivity is when a material has absolutely zero resistance. How does super conductors occur? What Is Superconductivity? Firstly, we need to know what resistance is. Resistance You can imagine it like this, you are trying to walk down a crowded hallway, and as you do, you are constantly bumping into other people which slow you down. The people in the hallway are the atoms and you are the electron flowing through the material. Less people, less resistance. History Discovery of superconductivity in 1911 by Dutch physicist by the name of Heike Kamerlingh Onnes, who was awarded the Nobel Prize for his field in 1913. Superconductivity By: David Liu, David Lai, Jackie Huang, and Paul Xue Copper wire X10^9 magnification + - - + + + + + + + + + + + + + + + + + - - - - e e e In 1933, two German researchers discovered a new property in superconductors. The Meissner effect was created. Starting in 1941, type 2 superconductors were being discovered and commercial superconductors were being developed Around 1935, an important theoretical advance in superconductivity was made by two brothers, They explained that if there was a mathematical relationship used in normal metals, there should be a separate mathematical relationship in superconductors. Their new mathematical relationship was able to explain the Meissner effect and Kamerlingh's perpetual current flow experiment. The first theory accepted to explain superconductivity was the BCS theory developed in 1957 by American physicists John Bardeen, Leon Cooper, and John Schrieffer. They were awarded the Nobel Prize in 1972. In 1986, the first high temperature superconductor was discovered by Karl Muller and Johannes Bednorz. The discoveries of high temperature superconductors are fairly recent, the first high temperature superconductor that does not contain copper was only discovered in the year 2000. Even to this day no theory can explain the properties of high temperature superconductors. In 1962, Brian D. Josephson he predicted that current will flow through 2 superconductors with any material in between. The flow of current through the non-superconductor or insulator was named the Josephson effect. He was awarded his share of the 1973 Nobel Prize. The next big discover about superconductivity was completed by two groups of people. What they discovered was called Energy gap or Band gap. This is the energy difference between its non-conductive state and its conductive state in a material. Type 1 and Type 2 Superconductors Applications of Superconductivity Superconductors The cooled temperature at which the material changes state is called the critical temperature. The change is known as a phase transition where the material basically instantly changes to an electrically resistive state. The messiner effect is simply a characteristic of superconductors where the magnetic field can only partially penetrate the material known as the diamagnetism of the superconductor causing it to levitate If the magnetic field is too strong or the current applied is too great, the messiner effect doesn't apply anymore and the superconductor abandons its electrically resistive state. Type 1 superconductors are usually pure metals that reach its critical temperature, shows no electrical resistance and displays perfect diamagnetism which means magnetic fields cannot penetrate it while in its superconductive state. Type 2 superconductors are usually alloys and are more commonly referred as ceramics. When type 2 superconductors are in a weak magnetic field they behave like type 1 superconductors but as it approaches its critical temperature it goes into a vortex state When the magnetic field is too great, the resistive state disappears. Type 2 superconductors have a higher tolerance to greater magnetic fields than type 1 superconductors. Lead (Pb)
Lanthanum (La)
Tantalum (Ta)
Mercury (Hg)
Tin (Sn)
Indium (In)
Palladium (Pd)
Chromium (Cr)
Thallium (Tl)
Rhenium (Re)
Protactinium (Pa)
Thorium (Th)
Aluminum (Al)
Gallium (Ga)
Molybdenum (Mo)
Zinc (Zn)
Osmium (Os)
Zirconium (Zr)
Americium (Am)
Cadmium (Cd)
Ruthenium (Ru)
Titanium (Ti)
Uranium (U)
Hafnium (Hf)
Iridium (Ir)
Beryllium (Be)
Tungsten (W)
Platinum (Pt)
Lithium (Li)
Rhodium (Rh) 7.196 K
4.88 K
4.47 K
4.15 K
3.72 K
3.41 K
3.3 K
3 K
2.38 K
1.697 K
1.40 K
1.38 K
1.175 K
1.083 K
0.915 K
0.85 K
0.66 K
0.61 K
0.60 K
0.517 K
0.49 K
0.40 K
0.20 K
0.128 K
0.1125 K
0.023 K
0.0154 K
0.0019 K
0.0004 K
0.000325 K Elements Critical Temperatures Type 1 Superconductors Thank You For Listening To Our Presentation Walther Messiner and Robert Ochsenfeld Fritz London above and Heinz London Brown, Zemansky, and Boorse + X10^9 magnification + - e e e - - Cooper Pairs e e e e e
e Pauli Exclusion Principle The Pauli exclusion principle is the quantum mechanical principle that no two identical fermions (particles with half-integer spin) may occupy the same quantum state simultaneously Fermions Bosons A phonon is a quantum mechanical description of a special type of vibrational motion, in which a lattice uniformly oscillates at the same frequency
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