Competing Orders and Quantum Phase Fluctuations on the Low-Energy   Excitations and Pseudogap Phenomena of Cuprate Superconductors
  We investigate the low-energy quasiparticle excitation spectra of cuprate superconductors by incorporating both superconductivity (SC) and competing orders (CO) in the bare Green's function and quantum phase fluctuations in the proper self-energy. Our approach provides consistent explanations for various empirical observations, including the excess subgap quasiparticle density of states, ``dichotomy'' in the momentum-dependent quasiparticle coherence and the temperature-dependent gap evolution, and the presence (absence) of the low-energy pseudogap in hole- (electron-) type cuprates depending on the relative scale of the CO and SC energy gaps. 
C.-T. Chen, A. D. Beyer, and N.-C. Yeh