A new theory of superconductivity has been formulated by a researcher at the University of Tsukuba’s Division of Quantum Condensed Matter Physics.
This model helps describe new experimental results better than the present theory depending on the calculation obtained by the “Berry connection.” The study may enable electrical grids in the future to transmit energy without any losses.
Superconductors are considered captivating materials that might look unexceptional at ambient conditions. However, upon cooling to very low temperatures, they permit electrical current to flow with zero resistance.
Superconductivity finds numerous applications such as lossless energy transmission, but the physics behind this process is yet to be understood clearly. The standard way of thinking about the transition from normal to superconducting is known as the Bardeen-Cooper-Schrieffer (BCS) theory.
In this model, until thermal excitations are maintained very small, particles can develop “Cooper pairs” that travel collectively and withstand scattering. But all kinds of superconductors are not properly described by the BCS model, which restricts the potential to make more powerful superconducting materials that operate at room temperature.
A researcher from the University of Tsukuba has now found a new superconductivity model that unravels the physical principles in a better way. Rather than concentrating on the pairing of charged particles, the new theory makes use of “Berry connection,” a mathematical tool. This value calculates a twisting of space where electrons tend to travel.
In the standard BCS theory, the origin of superconductivity is electron pairing. In this theory, the supercurrent is identified as the dissipationless flow of the paired electrons, while single electrons still experience resistance.
Hiroyasu Koizumi, Study Author and Professor, University of Tsukuba
To demonstrate, Josephson junctions are built when two superconductor layers are isolated by a thin barrier created by an insulator or a normal metal. Josephson junctions are extensively used in high-precision quantum computers and magnetic field detectors, but they do not fit neatly within the BCS theory.
In the new theory, the role of the electron pairing is to stabilize the Berry connection, as opposed to being the cause of superconductivity by itself, and the supercurrent is the flow of single and paired electrons generated due to the twisting of the space where electrons travel caused by the Berry connection.
Hiroyasu Koizumi, Study Author and Professor, University of Tsukuba
Hence, this study might pave the way for developments not just in quantum computing but also in the area of energy conservation.
Journal Reference:
Koizumi, H., (2021) Superconductivity by Berry Connection from Many-body Wave Functions: Revisit to Andreev−Saint-James Reflection and Josephson Effect. Journal of Superconductivity and Novel Magnetism. doi.org/10.1007/s10948-021-05905-y.