2 4 Ja n 20 08 Competing orders and the doping and momentum dependent quasiparticle excitations in cuprate superconductors ⋆

The low-energy quasiparticle excitations in hole-and electron-type cuprate super-conductors are investigated via both experimental and theoretical means. It is found that the doping and momentum dependence of the empirical low-energy quasiparti-cle excitations is consistent with a scenario of coexisting competing orders and su-perconductivity in the ground state of the cuprates. This finding, based on zero-field quasiparticle spectra, is further corrobarated by the spatially resolved vortex-state scanning tunneling spectroscopy, which reveals pseudogap-like features consistent with a remaining competing order inside the vortex core upon the suppression of superconductivity. The competing orders compatible with empirical observations include the charge-density wave and spin-density wave. In contrast, spectral characteristics derived from incorporating the d-density wave as a competing order appear unfavorable in comparison with experiments.