A researcher from the University of Tsukuba presents a new theoretical model for high-temperature superconductivity, in which an electric current can flow without resistance, which could lead to highly efficient power generation and transmission.
A scientist in the Department of Quantum Condensed Matter Physics at the University of Tsukuba has formulated a new theory of superconductivity. Based on the Berry connection calculation, this model can better explain the new experimental results than the current theory. The work could allow future power grids to transmit power without losses.
Superconductors are wonderful materials that might seem trivial under ambient conditions, but when cooled to extremely low temperatures, they allow electric current to flow without resistance. There are many obvious applications of superconductivity, such as lossless energy transfer, but the physics behind this process is still not clearly understood. A well-established way of thinking about the transition from a normal to a superconductor is called the Bardeen-Cooper-Schrafffer (BCS) theory. In this model, as long as the thermal excitation is kept small enough, the particles can form “Cooper pairs” that 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 superconductivity model that better reveals physical principles. Instead of focusing on the coupling of charged particles, this new theory uses the mathematical tool called the Berry connection. This value calculates the torsion of space where the electrons are moving. “In standard BCS theory, the origin of superconductivity is the coupling of electrons. In this theory, the supercurrent is defined as the flow without the dissipation of the paired electrons, while the single electrons are always subject to resistance,” explains Professor Hiroyasu Koizumi.
By way of illustration, Josephson junctions form when two superconducting layers are separated by a thin metallic barrier or insulator. Although they are widely used in high-resolution magnetic field detectors and quantum computers, Josephson junctions also do not quite match the internal BCS theory. “In the new theory, the role of electron coupling is to stabilize the Berry connection, rather than to cause superconductivity per se, and the supercurrent is the flow of single and double electrons caused by the twisting of space where the electrons travel due to Berry correlation,” says Professor Koizumi. Thus, this research may lead to advances in quantum computing as well as energy conservation.
Reference: “Superconducting through the Berry Connection of Multi-body Wave Functions: Revisiting Andrev – The St. James Reflection and the Josephson Effect” by Hiroyasu Koizumi, July 5, 2021, Journal of Superconductivity and New Magnetism.