الفهرس 
Chapter 1Only 14 pages are availabe for public view
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Abstract
Superconductivity is the phenomenon which describes a new phase of material in which its resistance drops to an immeasurable small value. The new phase is called superconducting phase. A perfect superconductor is a material that exhibits two characteristic properties, namely zero electrical resistivity (figure 1.1a) and perfect diamagnetism (figure 1.1b) when it is cooled below a particular temperature called the superconducting transition temperature Tc. At high temperature, it behaves like a normal metal and ordinarily is not a good conductor. For example lead, tantalum and tin become superconductors at Tc = 7.2 K, 4.47 K and 3.7 K, respectively. On the other hand, copper, silver and gold, which are much better conductors, do not become superconductors at these temperatures. In the normal state, above Tc, some superconducting elements are weakly diamagnetic and some are paramagnetic. Below Tc, they exhibit perfect electrical conductivity and also perfect or quite pronounced diamagnetism.
Perfect diamagnetism, means that superconducting materials do not permit an externally applied magnetic field to penetrate into its interior. This phenomenon is called Meissner effect and it is shown in figure 1.1b. Those superconductors that totally exclude an applied magnetic flux are known as Type I superconductors and the field at which this happens is called the thermal critical magnetic field Bc as shown in figure 1.2a. Other superconductors, called Type II superconductors, are also perfect conductors but their magnetic properties are more complicated. This Type of superconductor has two different critical magnetic fields represented by lower critical magnetic field Bc1 and upper critical magnetic field Bc2 as shown in figure 1.2b. For small values of applied field B, the Meissner effect leads to M = -B and there is no magnetic flux density inside the sample, B = 0. However in a type II superconductor once the field exceeds Bc1, magnetic flux start to enter the superconductor and hence B ≠ 0 (vortex or mixed state), and M is closer to zero than the full Meissner value of -B. With the further increase of B, up to Bc2, the superconductivity is destroyed and M = 0.