Low Temperature Physics

In the early 20th century, with the advancement of physicists’ ability to reach low temperatures, the behavior of the electrical resistance of highly pure metals at low temperatures came under study. One of the accessible metals was mercury, and Onnes observed for the first time that its electrical resistance sharply decreases and becomes zero at 4 Kelvin. Onnes named this newly observed state below 4 Kelvin as the superconducting phase and referred to the temperature threshold at which the material’s resistance reaches zero as the superconducting transition temperature.

Following this discovery, efforts continued to find other superconducting materials and higher transition temperatures. Cuprate oxide compounds, discovered from the late 1980s, exhibited different characteristics from low-temperature superconductors that were described by the BCS theory. The transition temperature for this type of superconductors was between 30 to 160 Kelvin, and they were called the first high-temperature superconductors.

Currently, in our lab, the compound YBCO is used as a copper-based superconductor. With a transition temperature of approximately 90 Kelvin (higher than the temperature of liquid nitrogen), this material can be employed as an infrared sensor, microwave filters, and more. The process of growing and testing the superconductivity of this material is carried out in our quantum transport laboratory, with the hope that in the near future, we will utilize this material for building optoelectronic devices.