OBSERVATION OF SELF-ORGANIZED CRITICALITY NEAR THE SUPERFLUID TRANSITION IN HE-4

We report on an experimental observation of self-organized criticality in He-4 very close to its superfluid transition. A constant temperatu re gradient, independent of the heat flux Q through the sample, is cre ated along a vertical column of He-4 by applying heat to the top of th e column. This constant temperature gradient equals the gravity-induce d gradient in the superfluid transition temperature, indicating that t he thermal conductivity of the sample has self-organized. The closenes s to criticality in this state is the same throughout most of the samp le, and it depends only on Q.