Theory of the quasi-particle spectra around a vortex in the two-dimensional t-J model

in order to clarify the microscopic structure of vortex cores in high-T-c superconductors, quasiparticle states are studied using the two-dimensional t-J model under a uniform magnetic field. The effect. of strong correlation is taken into account via Gutzwiller approximation. The dependence on J/t and the doping rate is discussed. The results show that an s-wave component is induced around the vortex core especially for the ion-doping case. in the nide range of doping rate, the local density of states near the core center has a zero-energy peak, which is due to the d-wave superconductivity. in the low doping regime, however, the zero-energy peak splits into two levels, which reflects the s-wave component induced around the core. These results may explain the recent experimental results of scanning tunneling spectroscopy in YBa2Cu3O7-delta.