Nonlinearity and interaction of second sound waves in superfluid 4He-3He mixture

摘要

We present the results of studies of nonlinear second sound waves in superfluid 4He-3He mixtures. Basing on the Hamiltonian approach the coefficient of mutual interaction of second sound waves is calculated and dependence of the nonlinearity coefficients of second sound on temperature and 3He concentration is determined. It is shown that introduction of 10% of 3He impurities into superfluid He II should result in lowering of the temperature T at which the nonlinearity coefficient changes its sing from negative to positive from 1.88 K to 1.67 K. Thus for weak 4He-3He solutions there exists a rather wide interval of temperatures below the superfluid transition temperature T, in which the nonlinearity coefficient of the second sound is negative and the shock front is formed at the trailing edge of the nonlinear second sound pulse of heating.