The influence of quenched disorder on the critical behavior of superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ is studied by confinement of the helium to the pores of three different porous media: Vycor, xerogel, and aerogel glasses. In each case a well defined power-law behavior for the superfluid density is observed as the transition temperature is approached. In Vycor the superfluid critical exponent is bulklike, whereas strikingly different critical exponents are seen in the other two media.

• Received 5 May 1988

DOI:https://doi.org/10.1103/PhysRevLett.61.1950