Spectral asymmetries in resonating-valence-bond states for cuprate superconductors

Samuel Bieri, ETH Lausanne, Switzerland.

Abstract: In the first part, I analyze the electronic Green's functions in the superconducting phase at zero temperature, using Gutzwiller-projected quasiparticles, and compare them to the conventional BCS form. Some of the properties of the BCS state are preserved by the projection: the total spectral weight is continuous around the node and approximately constant along the Fermi surface. On the other hand, the overall spectral weight is reduced by the projection with a momentum-dependent renormalization, and the projection produces an electron-hole asymmetry in the renormalization of the coherent spectral weights away from the node at low doping. The latter asymmetry leads to the bending of the effective Fermi surface which we define as the locus of equal electron and hole spectral weight. In the second part, I discuss a model for the pseudogap phase at intermediate temperature in the underdoped compounds. We model this phase by classical fluctuations of the SU(2) order parameter between the d-wave superconductor and the staggered-flux state. Although our mean-field approach neglects the explicit Gutzwiller-projection, we use parameters to model variational quasiparticles of the t-J model. Our model predicts a photoemission spectrum with an asymmetric gap structure interpolating between the superconducting gap centered at the Fermi energy and the asymmetric staggered-flux gap. This asymmetry of the gap changes sign at the points where the Fermi surface crosses the diagonal (π,0) – (0,π).

References: S. Bieri and D. Ivanov, PRB 75, 35104 (2007).
References: S. Bieri and D. Ivanov, arXiv:0809.5230 (PRB in press).