Intrinsic pinning of vorticity by domain walls of l texture in superfluid 3He-A

We present the first observation of substantial persistent flow in superfluid 3He-A in thick simply connected slabs in a zero magnetic field, but only in l textures with domain walls. The flow is induced in a rotating cryostat using a torsional oscillator as a probe. The hysteretic dependences of the trapped vorticity on the maximal angular velocity of rotation are fairly universal for different densities of domain walls and slab thicknesses. A model of a critical state set by either the critical velocity for vortex nucleation or pinning strength explains all observations.