THEORY OF THE QUASI-PARTICLE SPECTRA AROUND A VORTEX IN THE 2-DIMENSIONAL T-J MODEL

The microscopic structure of vortex cores in high-T-c superconductors is studied using the two-dimensional t-J model under a uniformly appli ed magnetic field. The spatial dependence of the pair potential is cal culated for various doping rates via the Gutzwiller approximation, in which the effect of strong correlation is taken into account. The resu lts show that, in the wide range of doping rates; the pair potential h as d-wave nature and the local density of states near the core center shows a zero-energy peak. However, in the low-doping region, an s-wave component is locally induced around the core and the zero-energy peak splits into two levels. This doping-dependence is characteristic of t he t-J model. Our results give a possible explanation for the experime ntal observation by scanning tunneling spectroscopy [Phys. Rev. Lett. 75 (1995) 2200] which demonstrates the splitting of the local density of states.