A new theory of superconductivity

A scientist from the Division of Quantum Condensed Matter Physics at the University of Tsukuba has formulated a new theory of superconductivity. Based on the calculation of the “Berry connection”, this model can explain the new experimental results better than the current theory. The work could allow future power grids to send energy without losses.

Superconductors are fascinating materials that may seem trivial under ambient conditions, but when cooled to very low temperatures, they allow electric current to flow with zero resistance. There are several obvious applications of superconductivity, such as lossless energy transmission, but the physics behind this process is still not clearly understood. The established way of thinking about the transition from normal to superconductor is called the Bardeen-Cooper-Schrieffer theory (BCS). In this model, as long as the thermal excitations are kept small enough, the particles can form “Cooper pairs” which travel together and resist diffusion. However, the BCS model does not adequately explain all types of superconductors, which limits our ability to create more robust superconducting materials that operate at room temperature.

Today, a scientist from the University of Tsukuba has developed a new model of superconductivity that better reveals physical principles. Instead of focusing on the pairing of charged particles, this new theory uses the mathematical tool called the “Berry connection”. This value calculates a torsion of the space where the electrons move. “In the standard BCS theory, the origin of superconductivity is the pairing of electrons. In this theory, the supercurrent is identified as the flow without dissipation of paired electrons, while single electrons always experience resistance,” explains the professor Hiroyasu Koizumi.

As an illustration, Josephson junctions form when two superconducting layers are separated by a thin normal metal barrier or insulator. Although widely used in high-precision magnetic field detectors and quantum computers, Josephson junctions also do not perfectly match internal BCS theory. “In the new theory, the role of electron pairing is to stabilize the Berry connection, instead of being the cause of superconductivity per se, and the supercurrent is the flow of single and paired electrons generated due to the twisting of the space where electrons travel because of the Berry connection, “says Prof. Koizumi. Thus, this research may lead to advances in quantum computing as well as energy conservation.