Forced oscillation of the A-B phase boundary in superfluid He-3

We present measurements conducted on the oscillating interface between supe rfluid He-3 A and B. The measurements, made at 150 mu K, are taken at frequ encies between 100 mHz, where the boundary moves almost in thermal equilibr ium with the fluid, and several kHz, where the boundary motion is highly no n-linear and out of equilibrium. Driving the oscillations to higher amplitu des seems to produce different friction mechanisms dominant only after cert ain thresholds. As yet these phenomenon have defied any explanation, theore tical or otherwise. (C) 2000 Published by Elsevier Science B.V. All rights reserved.