Tunneling asymmetry in high-Tc cuprates : possible evidence for a submerged band with nondegenerate fermions

It is shown that normal-state in-plane tunneling experiments in the high-T c cuprates can provide evidence for the existence of a submerged band containing nondegenerate fermions. These carriers arise in a model described by two two-dimensional holelike subbands with the chemical potential lying close to the top of the lower band. The resulting jump in the density of states near the Fermi level manifests itself in the observed asymmetry in tunneling conductance with respect to the bias voltage in metal-insulator-cuprate junctions. In the off-stoichiometry systems the jump also results in peaks in d 2 I/dV 2 . Implications of the model for the symmetric cuprate-insulator-cuprate junctions are discussed as well