Superconducting gap
= Superconducting gap
The gap feature in a superconducting single-particle excitation spectrum. In a simple BCS model, excitations have $E_{\mathbf k}=\sqrt{\xi_{\mathbf k}^2+|\Delta(\mathbf k)|^2}$. The <superconducting gap function> specifies the pairing amplitude and its phase; its magnitude need not be constant, and nodes can leave gapless excitations.