Theory of the quasiparticle spectra around a vortex in the two-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 applied magnetic field. The spatial dependence of the pair potential is calculated for various doping rates via the Gutzwiller approximation, in which the effect of strong correlation is taken into account. The results show that, in the wide range of doping rates; the pair potential has 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 the t-J model. Our results give a possible explanation for the experimental observation by scanning tunneling spectroscopy [Phys. Rev. Lett. 75 (1995) 2200] which demonstrates the splitting of the local density of states.