NIST solving a mystery among electrons

When it comes to sleuthing in science, few are better than the intrepid investigators at the National Institute of Standards and Technology (NIST). For example, take the “Case of the Stray Electrons.”

NIST researchers have created nanoscale devices that manipulate electrons in order to count them one at a time. Such counting is critical to the development of new fundamental electrical standards. When two electrons are bound in pairs (called Cooper pairs) in a superconductor, they can be manipulated much faster, providing larger currents that can be measured more accurately. Manipulation of Cooper pairs also is important in several schemes to develop quantum computers. Past attempts at manipulation, however, have been thwarted by the existence of a small number of unpaired electrons rambling around in the superconducting state. Avoiding these unpaired electrons is the mystery that NIST is now helping solve.

NIST researchers have uncovered an important clue by showing that a previously unappreciated factor has a strong effect on the number of unpaired electrons in Cooper pair devices. Electron counting devices are made from two layers of aluminum, where the strengths of the bonds pairing electrons in each layer can be different. This slight difference originally was thought to be unimportant. However, a study of more than a dozen devices in which this difference was varied in a controlled way and independently measured in each device, shows the difference does affect device performance directly.