Velocity of propagation of the 3He A → B transition

The first-order phase transition between the superfluid A and B phases of liquid 3He is strongly hypercooled, so that its propagation velocity cannot be determined by the usual thermal considerations. We present the essentials of a theory in which the limiting friction is due to the momentum change suffered by Bogoliubov quasi particles on Andreev reflection from, or transmission across, the moving interface, and we show that it gives reasonable agreement with the existing experimental data. (7 refs.)