COUNTERFLOW-DRIVEN TEXTURAL PHASE-TRANSITIONS IN SUPERFLUID HE-3-A(1)

We have studied second sound propagation through superfluid He-3-A(1) filling a rectangular resonator equipped with 3 pairs of transducers. The (l) over cap-texture was manipulated using one transducer to drive an oscillatory counterflow while measuring the resonant response of a n orthogonal transducer pair. We observed abrupt signal changes and hy steresis effects depending on drive frequencies and amplitudes. We ana lyzed our experiments by examining planar (l) over cap-textures strong ly coupled to the linear second sound wave equation. Evidence of first -order phase transitions was obtained numerically. The results are qua litatively consistent with the experimental findings. Our physical int uition did not anticipate these striking discontinuous phenomena.