CONTRACTION OF AEROGELS BY SUPERFLUID ORDER

We measured the thermal expansion dL/L of silica aerogels filled with liquid He-4. A rapid contraction of tile gel is observed at T-c0 sligh tly below T-lambda at decreasing T. We found an additional expansion d ue to fountain pressure gradients. It suddendly decreases at a tempera ture T-c(< T-c0). We interpret T-c as a critical temperature above whi ch superfluid exists only in some regions.