Staggered currents in the mixed state

The current pattern in the mixed state of high- T_c superconductors is studied in the U(1) mean-field theory of the t-J model. Assuming the absence of spin antiferromagnetism we find (1) at moderate doping staggered-current pattern exists in vortex cores and eventually percolates with increasing magnetic field. (2) The polarity of the staggered current is pinned by the magnetic field. (3) Vortex cores with (without) staggered current are slightly negatively (positively) charged. (4) Gutzwiller projection does not wash out the staggered current. We discuss the signature of staggered current in neutron scattering and scanning tunneling microscopy.