Kyoto, Japan -- As we witness the detrimental effects of climate change, the need for a rapid shift to renewable energy is only becoming more urgent. One of the most efficient forms of renewable energy, solar power, is generated by solar cells, which are the building blocks of solar panels. These electronic devices use semiconductors to convert the energy of light into electricity, a process called the photovoltaic effect.

Conventional solar cells have fundamental limitations in output voltage and conversion efficiency. A phenomenon called the bulk photovoltaic effect, which has attracted much attention in recent years, may enable highly efficient solar energy conversion without such limitations. However, the essential physics of the bulk photovoltaic effect have not been fully understood.

This effect originates from quantum phenomena and involves the asymmetric photoexcitation behavior of electrons, causing a steady electrical charge flow called a shift current, which is usually generated in the system with space-inversion symmetry. Another current materializes when there is a break in time-reversal symmetry, or the symmetry of physical laws when the flow of time is reversed. Since time-reversal symmetry is broken in magnetic materials, new effects related to the bulk photovoltaic effect are expected to arise in magnetic systems, but many aspects of these systems remain unexplained both theoretically and experimentally.