Superfluid Density Near the Lambda Point in Helium Under Pressure
The second-sound properties and the superfluid density deduced therefrom should be most fundamental in the study of the λ transition because they are inherently related to the critical modes and the coherence of the λ transition, respectively.1 Furthermore, there seems to exist a widely held precept of critical-point theory which indicates that the character of the critical behavior is independent of the material provided the symmetry properties of the Hamiltonian are the same. The precept has been supported to some extent by a number of theoretical studies,2 while Baxter3 has recently carried out a detailed calculation of the critical exponents in a rather special system, the two-dimensional Ising lattice, giving a conclusion against the above precept. No direct experimental study has been done of this problem, and, in this connection, it should be quite effective to look at critical exponents associated with the λ transition as a function of pressure because the pressure does not change the symmetry of the system as long as helium is in the liquid state. The present paper reports the change of the critical exponent of the superfluid density as a function of the pressure.
KeywordsCoherent State Critical Exponent Symmetry Property Critical Behavior Helium Atom
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