We have investigated the influence of impurities on the possible supersolid transition by systematically enriching isotopically-pure 4He (< 1 ppb of 3He) with 3He. The onset of nonclassical rotational inertia is broadened and shifts monotonically to higher temperature with increasing 3He concentration, suggesting that the phenomenon is correlated to the condensation of 3He atoms onto the dislocation network in solid 4He.
@article{arxiv.0710.3370,
title = {The effect of 3He impurities on the nonclassical response to oscillation of solid 4He},
author = {E. Kim and J. S. Xia and J. T. West and X. Lin and A. C. Clark and M. H. W. Chan},
journal= {arXiv preprint arXiv:0710.3370},
year = {2009}
}