Superconductivity
One of the most significant properties of solids is that certain metals and alloys exhibit almost zero resistivity when cooled to a sufficiently low temperature. This phenomenon is known as superconductivity. H K Onnes (1911) observed that as purified mercury is cooled, its resistivity vanishes abruptly at 4.2K. Onnes recognized this as a new phenomenon and termed it superconductivity. The temperature at which the substance loses its resistivity and transforms into the superconducting state is the critical temperature (Tc). Superconducting transition is reversible. The substances show different physical states and properties below and above the transition temperature. Magnetic behavior changes in the superconducting state The superconductor behaves as a diamagnet. Meissner effect: If we keep a specimen in a magnetic field at room temperature, the magnetic flux lines penetrate the substance (Figure 1). If we reduce the temperature to T< Tc, the f