Superconductivity is a fascinating and complex phenomenon that has intrigued scientists for over a century. It is a state of matter that exhibits remarkable properties, the most notable of which is the complete disappearance of electrical resistance. This article will introduce the basic concepts and definitions related to superconductivity.
Superconductivity is a quantum mechanical phenomenon where certain materials exhibit zero electrical resistance and expulsion of magnetic fields when cooled below a certain temperature, known as the critical temperature (Tc). This means that an electric current can flow indefinitely without any loss of energy, which is not observed in ordinary conductive materials.
The critical temperature, often denoted as Tc, is the temperature below which a material becomes superconducting. Above this temperature, the material behaves as a normal conductor with electrical resistance. The critical temperature varies for different materials. For example, for mercury, the first material in which superconductivity was discovered, Tc is 4.2 Kelvin.
In the context of superconductivity, the term "state" refers to the physical state of a material. When a superconductor is cooled below its critical temperature, it transitions from the normal state to the superconducting state. In the normal state, the material exhibits electrical resistance, while in the superconducting state, it shows zero electrical resistance and perfect diamagnetism.
Zero electrical resistance is one of the defining characteristics of superconductors. When a material becomes superconducting, it can carry an electric current without any energy loss. This is in stark contrast to ordinary conductors like copper or silver, which always have some resistance and thus lose energy in the form of heat when an electric current passes through them.
The Meissner effect, named after the German physicist Walther Meissner, is another fundamental property of superconductors. When a material transitions into the superconducting state, it expels all the magnetic fields from its interior, a phenomenon known as perfect diamagnetism. This is the principle behind the levitation of a magnet above a superconductor, a popular demonstration of superconductivity.
In conclusion, understanding these basic concepts and definitions is crucial for delving deeper into the study of superconductivity. The zero electrical resistance and the Meissner effect are the two key properties that set superconductors apart from ordinary conductors and make them invaluable for a wide range of applications.