Abstract
The interface of phase-separated He3-He4 mixtures, when charged with negative ions, shows a pronounced softening of its ripplon spectrum at wave vectors around the inverse capillary length. As the electrical field perpendicular to the interface is increased beyond a value Ec where the frequency of the soft ripplon vanishes, a phase transition to a spontaneous deformation of the interface in the form of an ordered array of dimples is observed.