Some calculations regarding the characteristic length for superfluidity in liquid helium

A superfluid characteristic length has consistently emerged from a variety of independent experiments on helium thin films. Both the magnitude and the temperature dependence of this quantity are now quite well defined within relatively narrow limits. This length appears to consist of two parts: the thickness of solid blanketing the substrate underneath the liquid film plus a pseudolength deriving from supplementary excitations in the system. The first contribution is directly calculated, and the results appear to fit experiment quite well. For the remaining pseudolength the parameters necessary for a surface-roton-excitation hypothesis to fit experiment are estimated. It is found, using the analysis presented, that the quantitative features of a surface-excitation spectrum may be deduced with considerable precision from presently available experimental data