Plane to see

Interface superconductivity in bilayer cuprate devices is sensitive to changes in just one layer of copper and oxygen atoms.

Credit: © 2009 AAAS

Materials that contain layers of copper and oxygen atoms are known as cuprates, and they can be both metals and insulators. However, when the correct amounts of elements such as lanthanum and strontium are added, cuprates can also become superconductors, losing their resistance to electrical current when cooled below a critical temperature. Last year a new phenomenon called interface superconductivity was discovered at the boundary between metallic and insulating cuprate layers by Ivan Bozovic of the Brookhaven National Laboratory and co-workers. Now Bozovic, Gennady Logvenov and Adrian Gozar have shown that interface superconductivity occurs within a single copper–oxygen plane¹.

The Brookhaven team used molecular beam epitaxy to grow a thin layer of La_1.56Sr_0.44CuO₄ (LSCO), which is metallic, on a substrate, followed by a thin layer of La₂CuO₄ (LCO), which is an insulator, to produce a bilayer structure containing a total of 12 CuO planes. During the growth process the team also replaced 3% of the copper atoms in one of the 12 planes with zinc, which is known to suppress superconductivity. Bozovic and co-workers observed interface superconductivity with a critical temperature between about 30 and 35 K in all their samples, apart from those that contained zinc atoms in the second LCO layer (highlighted in yellow in the image), which had a critical temperature of 18 K. The results show that interface superconductivity occurs within this plane of copper and oxygen atoms.