https://www.sciencedaily.com/releases/2020/06/200629120113.htm

Condensed matter physicist Doug Natelson and his colleagues at Rice and the University of Colorado Boulder discovered this massive emission from a nanoscale gap between two electrodes made of plasmonic materials, particularly gold.

The lab had found a few years ago that excited electrons leaping the gap, a phenomenon known as tunneling, created a larger voltage than if there were no gap in the metallic platforms.