Researchers in the US have discovered how to manipulate electrons at oxide interfaces by inserting a single layer of atoms. Chang-Beom Eom and colleagues inserted a monolayer of a rare earth element between two pieces of precisely grown strontium titanate and found that they could produce an electron "fluid" in this layer, with many interesting and potentially useful characteristics. This research is the first demonstration of strong correlation among electrons at an oxide interface. The electron layer displayed distinct characteristics depending on the particular rare-earth element the team used. Materials with larger ionic radii, such as lanthanum, neodymium and praseodymium, are conducting, whereas materials with smaller radii, including samarium and yttrium, are insulating. "This advancement could make a broad impact in fields even beyond physics, materials or chemistry," Eom says. "People can use the idea that an interface made from a single atomic layer of different ions can be used to create all kinds of properties."