A team of researchers from Cornell University, Ithaca, NY, and Brookhaven National Laboratory, Upton, NY, have demonstrated how to switch a particular transition metal oxide, a lanthanum nickelate (LaNiO3), from a metal to an insulator by making the material less than a nanometer thick.
Continually shrinking electronic devices could get as small as atomic dimensions with the help of transition metal oxides, a class of materials that seems to have it all, they say: superconductivity, magnetoresistance, and other exotic properties.
The team of researchers used an extremely precise growth technique called molecular-beam epitaxy (MBE). They synthesized atomically thin samples of the lanthanum nickelate and discovered that the material changes abruptly from a metal to an insulator when its thickness is reduced to below 1 nanometer. When that threshold is crossed, its conductivity turns off like a light switch, which could prove useful in nanoscale switches or transistors.
Using a one-of-a-kind system at Cornell, which integrates MBE film growth with a technique called angle-resolved photoemission spectroscopy, the scientists mapped out how the motions and interactions of the electrons in the material changed across this threshold, varying the thickness of their oxide films atom by atom. They discovered that when the films were less than 3 nickel atoms thick, the electrons formed an unusual nanoscale order, akin to a checkerboard. Their discovery paves the way for making advanced new electronic devices from oxides.