الفهرس 
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Abstract
Generally speaking, the discovery of superconductivity has been recognized as one of the greatest scientific achievements of the twentieth century. Superconductivity phenomenon can be defined as the state at which the current can flow in a material without noticeable energy dissipation. It is accompanied by a sudden DROP of the electrical resistance to zero by cooling below a critical temperature called the superconducting transition temperature Tc, see Figure 1.1(a). Superconductivity was first discovered in mercury by Onnes [1] in 1911. The temperature at which mercury becomes superconducting was found to be very close to the boiling point of liquid helium at 4.2 K. Subsequently, superconductivity was discovered in many metals, alloys and intermetallic compounds. Besides the lack of resistance, another characteristic of superconductivity is the ”Meissner effect”, discovered by Meissner and Ochsenfeld in 1933 [2]. It is found that the superconductor expels the magnetic field from inside it, while the ideal conductor maintains its interior field. Thus, superconductors are not just perfect conductors but also perfect diamagnetism. This is called the Meissner effect as shown in Figure 1.1(b).