Damping of first sound and viscosity of liquid 3He‐B near superfluid transition

Abstract

The viscosity of normal fluid component of the isotropic B phase of liquid 3He in the vicinity of the superfluid transition temperature was measured from the damping of 22‐kHz first sound in a cylindrical resonator. In the normal fluid region, the viscosity, η, varies like T−2 as expected, where T is temperature. In the superfluid phase, just below the transition temperature Tc, η decreases very rapidly. The reduced viscosity η (T)/η (Tc) is 0.5 at 1% of Tc, and less than 0.25 within 10% of Tc. The change in viscosity is found to vary with the simple energy gap temperature dependence given by (1 − T/Tc)1/2 only within a narrow temperature range 1 − T/Tc ≲ 10−3. The measured η (T)/η (T)c is in qualitative agreement with the results of torsion oscillator experiments. [Work supported by NSF.]