Title: Probing the Upper Limit of Non-classical Rotational Inertia in
Solid Helium 4

abstract:

We study the effect of confinement on solid 4He's non-classical rotational inertia (NCRI)[1] in a torsional oscillator by
constraining it to narrow annular cells of various widths. The NCRI exhibits
an observed maximum value of 20% for annuli of ~ 100 micro-m samples constrained to porous media or to larger geometries both
have smaller NCRI,mostly below ~ 1%. In addition, we extend Kim and Chan's blocked annulus experiment[2] to solid samples with
large supersolid fractions.
Blocking the annulus suppresses the non-classical decoupling from 17.1% below the limit of our detection of 0.8%. This result
demonstrates the nonlocal nature of the supersolid phenomena. At 20 mK, NCRI depends on velocity history[3] showing a closed
hysteresis loop in different thin annular cells.

[1]Leggett, A.J.  Can a solid be "Superfluid"? Phys. Rev. Lett. 25, 1543(1970).
[2]Kim, E. and Chan, M.H.W.  Observation of superflow in solid helium. Science 305, 1941(2004).
[3]Aoki, Y., Graves, J.C., and Kojima, H.  Oscillation frequency dependence of nonclassical rotation inertia of solid He-4.
Phys. Rev. Lett. 99, 015301(2007).