A layering model for superconductivity in the borocarbides

We propose a superlattice model to describe superconductivity in layered materials, such as the borocarbide families with the chemical formulæ RT₂B₂C and RTBC, with R being (essentially) a rare earth, and T a transition metal. We assume a single band in which electrons feel a local attractive interaction (negative Hubbard-U) on sites representing the TB layers, while U = 0 on sites representing the RC layers; the multi-band structure is taken into account minimally through a band offset ε. The one-dimensional model is studied numerically through the calculation of the charge gap, the Drude weight, and the pairing correlation function. A comparison with the available information on the nature of the electronic ground state (metallic or superconducting) indicates that the model provides a systematic parametrization of the whole borocarbide family.