Cryotron
A cryotron (kryos (Greek) = frost, tron (Greek) = device) or superconductor switching element is a switch whose mode of operation is based on the principle that superconductivity can be suppressed by magnetic fields.
The cryotron consists of a piece of tantalum that is wrapped in a coil made of niobium and operated at temperatures of liquid helium . Due to the superconductivity, current flows through the tantalum without resistance. However, if current is passed through the niobium coil, the superconductivity in the tantalum breaks down due to the induced magnetic field, whereby the current is weakened or interrupted.