Nanoimpurities in the superfluid 3He

Qualitative difference of aerogel as impurity in the superfluid 3He with respect to atomic impurities in metals is large cross-section of scattering of quasiparticles by the strands of aerogel and as a consequence essential role of static fluctuations of the order parameter. These fluctuations can be described phenomenologically by introduction of a static random field in the Ginzburg and Landau functional. It is discussed here how to find the random field starting from a microscopic structure of aerogel and as an example, a simple model of randomly distributed spheres is considered.