Gap and subgap tunnelling in cuprates

Abstract

We describe strongly attractive carriers in cuprates in the framework of a simple quasi-one dimensional Hamiltonian with a local attraction. In contrast with the conventional BCS theory there are two energy scales, a temperature independent incoherent gap $\Delta_p$ and a temperature dependent coherent gap $\Delta_c (T)$ combining into one temperature dependent global gap $\Delta=(\Delta_p^2 +\Delta_c^2)^{1/2}$. The temperature dependence of the gap and single particle (Giaver) tunnelling spectra in cuprates are quantitatively described. A framework for understanding of two distinct energy scales observed in Giaver tunnelling and electron-hole reflection experiments is provided.