It was also a cuprate that was discovered with a critical temperature above the boiling point of liquid nitrogen (77 K). This led to the realization that applications of superconductivity were looking more realistic and feasible in the near future . Superconductors with a critical temperature above the boiling point of liquid nitrogen are called hightemperature superconductors. It is important to note that all high-temperature superconductors are type-II superconductors. To date, cuprate superconductors hold the record for the highest critical temperature at atmospheric pressure. In the past few years, other materials have demonstrated high critical temperatures, but only at extremely high pressures . Fig. shows a timeline of the discovery of superconductors and their critical temperatures.