Abstract
Direct observation of superfluid response in para-hydrogen () remains a challenge because of the need for a probe that would not induce localization and a resultant reduction in superfluid fraction. Earlier work [H. Li, R. J. Le Roy, P.-N. Roy, and A. R. W. McKellar, Phys. Rev. Lett. 105, 133401 (2010)] has shown that carbon dioxide can probe the effective inertia of although larger clusters show a lower superfluid response due to localization. It is shown here that the lighter carbon monoxide probe molecule allows one to measure the effective inertia of clusters while maintaining a maximum superfluid response with respect to dopant rotation. Microwave spectroscopy and a theoretical analysis based on Feynman path-integral simulations are used to support this conclusion.
- Received 31 July 2011
DOI:https://doi.org/10.1103/PhysRevLett.108.253402
© 2012 American Physical Society