The fact that helium becomes superfluid at extremely low temperatures is a well-known quantum mechanical phenomenon. Objects do not experience any friction when they move through superfluid helium – at least, as long as they move slower than the critical Landau velocity. So far, scientists have only been able to verify this for bulk helium. The new research has now shown that even in tiny nanodroplets, helium still exhibits superfluidity.
The pioneering experiment is the result of a collaboration between dr. Marcel Drabbels (EPFL, former postdoc at FOM Institute AMOLF) and FOM workgroup leader and UvA researcher prof.dr. Wybren Jan Buma. The experiment starts with the production of extremely cold helium nanodroplets having a temperature of 0.4 K and a size that can be varied from a few million to less than thousand helium atoms. Subsequently, the researchers place one single metal atom or one single molecule in such a nanodroplet.
Due to the weak attractive interactions it experiences with helium, the ‘impurity’ will initially be located at the center of the nanodroplet. Next, the researchers activate the impurity with a nanosecond laser pulse. The electronically excited particle now experiences a repulsive interaction with the helium. As a result the atom or molecule is launched out of the droplet. There its speed is determined.
Read more at: Phys.org