Memory device employing hysteretic properties of a tungsten filament in superfluid helium-4

A tungsten filament immersed in superfluid helium has strong hysteretic $I$-$V$ characteristics. By increasing the applied voltage, a remarkable current drop occurs at a transition voltage, at which the filament enters a non-ohmic hot state and becomes covered with a helium gas sheath. The return to an ohmic state occurs at a lower voltage because of the poor heat conduction of the gas sheath. Hence, the $I$-$V$ characteristic is strongly hysteretic. The stable hysteresis window was employed to fabricate a novel memory device, which demonstrated fast switching and stable reading.