Structure of a Vortex in thet−JModel

We study the single-vortex solution of the $t-J$ model within resonating-valence-bond mean-field theory. We find two types of vortex cores, insulating and metallic, depending on the parameters of the model. The pairing order parameter near both cores have $d_{x^2{-y}^2}+i\eta d_{\mathrm{xy}}$ symmetry. For some range of $t/J$ the calculated tunneling spectrum of the metallic vortex core agrees qualitatively with the STM tunneling data for BSCCO.