  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.
