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The damping of second sound near the superfluid transition in ⁴He

University of British Columbia

The attenuation of second sound near the superfluid transition in ⁴He has been determined by measuring the decay time for free oscillations of plane wave modes in a resonant cavity. The results for both the critical exponent and amplitude of the second sound damping coefficient are consistent with the early predictions of Hohenberg, Siggia and Halperin based on renormalization group theory. However, the damping observed in this work is less than the recent predictions of a non-linear renormalization group analysis by Dohm and Folk. The measurements cover the temperature interval 1.8 x 10⁻⁵ ≲ t ≲ 2.1 x 10⁻², where t = (T[sub λ] - T)/T[sub λ]. Fitting the results to a single power law for t < 10⁻³, the critical exponent governing the temperature dependence is found to be 0.31 ± 0.05. If the results are constrained to obey the theoretical asymptotic temperature dependence with an exponent of 0.288, then the amplitude obtained for the damping is 3.7 ± 0.4 cm² s⁻¹. This corresponds to a value for the universal amplitude ratio, R₂, of 0.11 ± 0.01. For t ≳ 10⁻³ the damping departs from the critical behaviour, and increases to obtain the values previously observed by Hanson and Pellam for t ≳ 10⁻².

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2010-03-29

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http://hdl.handle.net/2429/22963

Physics

University of British Columbia

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