Theory of vortex lattice effects on STM spectra in d-wave superconductors

The theory of scanning tunneling spectroscopy of low-energy quasiparticle (QP) states in vortex lattices of d-wave superconductors is developed taking account of the effects caused by an extremely large extension of QP wavefunctions in the nodal directions and the band structure in the QP spectrum. The oscillatory structures in STM spectra, which correspond to van Hove singularities, are analyzed. Theoretical calculations carried out for finite temperatures and scattering rates are compared with recent experimental data for high-T _c cuprates.