Evidence for Superfluidity in Para-Hydrogen Clusters Inside Helium-4 Droplets at 0.15 Kelvin
Slava Grebenev,1*
Boris Sartakov,2
J.
Peter Toennies,1
Andrei F. Vilesov1*
A linear carbonyl sulfide (OCS) molecule surrounded by
14 to 16 para-hydrogen (pH2) molecules, or
similar numbers of ortho-deuterium (oD2) molecules,
within large helium-4 (4He) droplets and inside mixed
4He/3He droplets was investigated by infrared
spectroscopy. In the pure 4He droplets (0.38 kelvin), both
systems exhibited spectral features that indicate the excitation of
angular momentum around the OCS axis. In the colder
4He/3He droplets (0.15 kelvin), these features
remained in the oD2 cluster spectra but disappeared in the
pH2 spectra, indicating that the angular momentum is no
longer excited. These results are consistent with the onset of
superfluidity, thereby providing the first evidence for superfluidity
in a liquid other than helium.
1 Max-Planck-Institut für
Strömungsforschung, Bunsenstra
e 10, 37073 Göttingen, Germany.
2 General Physics
Institute, Russian Academy of Sciences, 117942 Moscow, Russia.
*
Present address: Ruhr-University Bochum, Physical Chemistry II,
D-44780 Bochum, Germany.
