Dynamics of mobile liquid bubbles in helium mixture crystals

We describe systematic heat-transport measurements of a 7.5% ${}^{3}{\mathrm{H}\mathrm{e}\ensuremath{-}}^{4}\mathrm{He}$ solid mixture coexisting with the liquid at temperatures near 1 K. We observed that under a temperature gradient, macroscopic liquid bubbles appear and move through the solid. Visually, this phenomenon resembles boiling. However, in our case the bubbles are formed and subsequently move from the cold side towards the hot side of the experimental cell. The bubbles move with a speed that depends linearly on the temperature gradient. We present a model explaining the motion of the bubbles as resulting from the dynamics of superfluid mixtures. A possible mechanism of bubble formation is discussed.