Future chips may operate at atomic dimensions
April 23, 2014
In an effort to shrink down electronic devices to atomic dimensions, researchers from Cornell University and Brookhaven National Laboratory have shown how to switch exotic transition metal oxide material from a metal to an insulator by making the material less than a nanometer thick.
Transition metal oxides seem to have it all: superconductivity, magnetoresistance, and other exotic properties. These possibilities have scientists excited to understand everything about these materials, and to find new ways to control their properties at the most fundamental levels.
The team of researchers, which published its findings online April 6 in Nature Nanotechnology (to appear in the journal’s May issue), chose a particular transition metal oxide, a lanthanum nickelate (LaNiO3).
Switching from metal to insulator
Using an extremely precise growth technique called molecular-beam epitaxy (MBE), the researchers 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 — the ability for electrons to flow through the material — switches off like a light, a characteristic that could prove useful in nanoscale switches or transistors, said lead researcher Kyle Shen, associate professor of physics.
The researchers 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.
The results demonstrate the ability to control the electronic properties of exotic transition metal oxides at the nanometer scale, as well as revealing the striking cooperative interactions that govern the behavior of the electrons in these ultrathin materials. Their discovery paves the way for making advanced new electronic devices from oxides.
The work was supported by the Kavli Institute at Cornell for Nanoscale Science, the Office of Naval Research, the National Science Foundation through the Cornell Center for Materials Research (MRSEC program), and the U.S. Department of Energy, Basic Energy Sciences.
Abstract of Nature Nanotechnology paper
In an effort to scale down electronic devices to atomic dimensions, the use of transition-metal oxides may provide advantages over conventional semiconductors. Their high carrier densities and short electronic length scales are desirable for miniaturization, while strong interactions that mediate exotic phase diagrams3 open new avenues for engineering emergent properties. Nevertheless, understanding how their correlated electronic states can be manipulated at the nanoscale remains challenging. Here, we use angle-resolved photoemission spectroscopy to uncover an abrupt destruction of Fermi liquid-like quasiparticles in the correlated metal LaNiO3 when confined to a critical film thickness of two unit cells. This is accompanied by the onset of an insulating phase as measured by electrical transport. We show how this is driven by an instability to an incipient order of the underlying quantum many-body system, demonstrating the power of artificial confinement to harness control over competing phases in complex oxides with atomic-scale precision.