Researchers have demonstrated that the direction of the spin-polarized current can be restricted to only one direction in a single-atom layer of a thallium-lead alloys when irradiated at room temperature. The discovery defies conventions: single-atom layers have been thought to be almost completely transparent, in other words, negligibly absorbing or interacting with light. The one-directional flow of the current observed in this study makes possible functionality beyond ordinary diodes, paving the way for more environmentally friendly data storage, ultra-fine two-dimensional spintronic devices, in the future.