Theory of asymmetric tunneling in the cuprate superconductors

We explain quantitatively, within the Gutzwiller-Resonating Valence Bond theory, the puzzling observation of tunneling conductivity between a metallic point and a cuprate high-Tc superconductor which is markedly asymmetric between positive and negative voltage biases. The asymmetric part does not have a ‘coherence peak’ but does show structure due to the gap. The fit to data is satisfactory within the over-simplifications of the theory; in particular, it explains the marked ‘peak-dip-hump’ structure observed on the hole side and a number of other qualitative observations. This asymmetry is strong evidence for the projective nature of the ground state and hence for ‘t-J’ physics.