Spin current in a two-dimensional electron gas tunnelling junction

We report a novel phenomenon of dissipationless spin current in nonmagnetic tunnelling junctions, composed of two high mobility two-dimensional electron gases (2DEG) with either Rashba or Dresselhaus spin-orbital interaction as well as an insulator barrier between them. We find that, at zero bias, an equilibrium spin current flows in the junction without any charge current. The physical origin is the exchange coupling between two pseudomagnetic fields in 2DEG leads and it is similar to the super current in a Josephson junction.