Very Small Tunnel Junctions Sense the Effect of Single Electrons

In most capacitors the gain or loss of a single electron is hardly noticed. But in the very small tunnel junctions that can now be made, the capacitance is so small—on the order of $10−16$ farads or less—that the addition of just one electron can change the electric potential across the barrier by several millivolts. In that case, a single electron certainly can make a difference. The change in potential when an electron tunnels across the junction is enough to impede the tunneling of the next electron. The resulting block of current flow—called the Coulomb blockade—should show up in the current‐voltage characteristics of small‐capacitance tunnel junctions at low temperatures.