Superconductivity- an overview
A new era begins with the discovery of superconductor material which works at high temperature. This field emerged as one of the most prominent research field in the material science during the last decade. The discovery of superconductivity aroused great interest in this field since the materials with no electrical resistance and negligible heat loss. These materials have application in different revolutionary areas such as superconducting magnets, high energy physics, transportation, digital circuits, RF, microwave filterers, SQUIDs (Superconducting quantum interference devices) and power stage device. The superconducting material exhibits zero resistance for the propagation of current below a certain sufficiently low temperature. They also show Meissner effect and macroscopic phenomena by virtue of which they expel total magnetic field from within.
The discovery of superconductivity was done by Kamerlingh Onnes in Leiden in 1911 while studying the resistivity of mercury at very low temperature 4.1 K, the melting point of the helium. It was observed that above 4.1 K temperature material behaves like a regular resistive material and resistance decreases suddenly below this temperature. Thus after the discovery of superconductivity, a lot of research has been done to synthesize the material which works at higher temperature due to the immense potential of high-temperature superconductivity. Researchers have worked on to increase the critical temperature of the existing superconducting material. They try to synthesize special kind of materials and manipulate their structure to increase their critical temperature. In 1986, Bednorz and Muller discover superconductor oxide La-Ba-Cu-O which showed high-Tc° makes another mark-able revolution in this area. The mechanism of superconductivity still remains elusive; a number of theories have been given to explain this phenomenon. London and London (1935) proposed a phenomenology theory by using Maxwell equations, Ginzburg and Landau (1950) proposed a semiphenomenological theory and Bardeen Copper and Scherieffer (1957) proposed microscopy theory. Among these theories, the microscopic BCS theory was the most successful theory to explain the superconductivity. In BCS theory, they argued that superconductivity behavior is due to the cooperative behavior of electrons, two electrons with equal and opposite momenta form a bound pair (Cooper pair). In 2017, Seokhwan Choi group has reported a new mechanism for switching magnetism and superconductivity in the material by using spin-polarized tunneling microscopy. They control the local superconductivity in a nontrivial C4 (2´2) order in Fe-layer by using spin-polarized tunneling current.