Anisotropic and inhomogeneous superfluidity in OCS-doped helium clusters

Path integral Monte Carlo calculations have been performed to analyze the quantum solvation structure around a single impurity molecule in doped helium-4 clusters. Using a new local superfluid estimator that is based on local decomposition of the moments of inertia of the quantum fluid, we obtain the anisotropic and inhomogeneous superfluid fraction of the surrounding helium. We find that unlike previous local estimators, this provides a consistent analysis of the response of the inhomogeneous quantum fluid to impurity rotation. Application to helium clusters doped with a linear OCS molecule shows that at T similar to 0.3 K, the superfluid response parallel to the molecular axis is complete in both first and second solvation shells around the molecule, but that the perpendicular superfluid response is significantly depressed in the first shell. The suppression of perpendicular superfluid response in the first shell results in the reduction of the rotational constant of OCS inside the droplets that was observed in spectroscopic experiments. (c) 2005 Elsevier Ltd. All rights reserved.