Apparent anomalous critical behaviour of superfluid helium 4 in porous Medium

The anomalous critical exponents of the superfluid ⁴He density in silica aerogels is analysed by a simple model where the distribution of pore size is assumed to be very broad. The strong modification of the critical behaviour is related to the structure of the aerogels skeleton which is discussed in terms of a percolation or alternatively a hierarchical sponge model.