Thermal and Quantum Fluctuations Induced Additional Gap in   Single-particle Spectrum of d-p model
  The possibility of thermal and quantum fluctuations induced attractive interaction leading to a pairing gap \Delta_tq in the single-particle spectrum of d-p model in the limit of a large N of fermion flavor is investigated analytically. This is an anomalous pairing gap in addition to the one with d-wave symmetry originating from partially screened, inter-site coulomb interaction. The motivation was to search for a hierarchy of multiple many-body interaction scales in high-Tc superconductor as suggested by recent experimental findings. The pairing gap anisotropy stems from more than one sources, namely, nearest neighbour hoppings and the p-d hybridization but not the coupling of the effective interaction. The temperature at which \Delta_tq vanishes may be driven to zero by using a tuning parameter to have access to quantum criticality only when N >> 1. For the physical case N = 2, the usual coherent quasi-particle feature surfaces in the spectral weight everywhere in the momentum space below the pairing gap \Delta_tq. Thus it appears that the reduction in spin degeneracy has the effect of masking quantum criticality. 
Partha Goswami