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Giant proximity effects in 4He at the superfluid transition

We have performed a series of measurements with 4He near the superfluid transition which have shown large coupling effects between regions of helium confined in welldefined geometries1. An analysis of these data, both specific heat and superfluid density, show that the coupling is governed by the three-dimensional correlation length ξ.
However, contrary to what one might have expected, effects of coupling are seen at distances larger than 10 times ξ. I will discuss the implications of these results and the
connection to other systems.

1. J. K. Perron, M. O. Kimball, K. P. Mooney and F. M. Gasparini Nat. Phys. 6, 499 (2010); and, J. K.
Perron and F. M. Gasparini, submitted to PRL.