Half quantum vortex in superfluid ³He-A phase in parallel-plate geometry

The half quantum vortex (HQV) in condensates has been studied, since it was predicted by Volovik and Mineev, and independently by Cross and Brinkman in superfluid ³He-A phase. However, no experimental evidence for its existence has been reported until recently. Motivated by a recent experimental report by Yamashita et al. (AIP Conf. Proc., 850 (2006) 185; private communication) we study the HQVs in superfluid ³He confined between two parallel plates with a gap D∼10 μm in the presence of a magnetic field H∼26 mT perpendicular to the parallel plates. We find that the bound HQVs are more stable than the singular vortices and free pairs of HQVs, when the rotation perpendicular to the parallel plates is below the critical speed, Ω_c=2∼12 rad/s, if the magnetic healing length, ξ_H is about 2–5 μm. The bound pair of HQVs accompanies the tilting of -vector out of the plane, which leads to an additional absorption in NMR spectra. Our study appears to describe the temperature and rotation dependence of the observed satellite NMR signal, which supports the existence of the HQVs in ³He.