Temperature Dependent Spatial Order in Superfluid and Normal 4He
Measurements of the structure factor S(k) for 4He at constant density above and below Tλ are reported. The results show a clear loss of spatial order on cooling through Tλ. Application of the theory of Cummings, Hyland, and Rowlands to the data allows a measurement of the condensate fraction for He II.
Robert Hallock, H. N. Robkoff, and D. A. Ewen. "Temperature Dependent Spatial Order in Superfluid and Normal 4He" Physical Review Letters 43.27 (1979): 2006-2009.
Available at: http://works.bepress.com/robert_hallock/42