Superconductors are materials that show no resistance to electrical current when cooled. Recently, scientists discovered a new superconducting material. It’s a thin film of iron and selenium on an insulating layer. The combination transmits electricity without loss when cooled to 24 Kelvin (minus 416 degrees Fahrenheit). Now, scientists have found that when exposed to low-energy ultraviolet light, the material acts as a superconductor at higher temperatures. That is, the critical temperature increases by 25 percent. Also, the new superconducting state remains stable even after the light is turned off.
Fast-switching, low-energy optical control offers a new way to manipulate superconductivity. The newly discovered effect may enable devices for next-generation quantum computers. Such computers could improve materials and drug discovery, which are difficult with today’s machines. Also, these computers could benefit artificial intelligence research and use. Finally, this work could aid quantum sensors. Such sensors could improve subsurface surveys and much more.
The phenomena of superconductivity was first discovered in 1911 in mercury cooled in liquid helium (about 4 Kelvin), and was subsequently seen in a variety of elemental and binary metals (for example, niobium and Nb3Sn). Superconductors are currently used for a broad range of applications, such as the construction of powerful magnets using for medical imaging (MRI) and in demonstration projects for the future electrical grid. Since that discovery, many new families of superconducting materials have been discovered, and these new materials are being explored for the development of new technologies such as quantum computers and quantum sensors. Among the newly discovered superconducting materials is iron selenide (FeSe) in the form of a monolayer film on a strontium titanate (SrTiO3) substrate. In general, superconductors do not respond to light. Scientists recently discovered something different for FeSe films—ultrafast laser pulses can be used to dramatically increase the temperature at which the material becomes superconducting, from 24 to 30 Kelvin. Subsequently, researchers from West Virginia University showed that the ultrafast lasers were not needed to realize this level of control. Instead, a 3.5 eV (ultra violet) light-emitting diode with less than 50 µW/cm2 intensity—comparable to a low power blacklight—could be used to switch the FeSe film into a superconducting state in a very short time. This superconducting state persisted for days unless a series of high voltage pulses was applied to the back of the substrate or the sample was warmed to room temperature and re-cooled. The newly discovered, photo-induced superconductivity effect in FeSe films is being explored for new applications as opto-quantum devices.
Work performed by C.C.’s group is supported by the Department of Energy Office of Science and by the National Science Foundation. Work performed by L.L.’s group is supported by the Department of Energy Office of Science.