Superconducting density of states from scanning tunneling microscopy

In Bardeen, Cooper and Schrieffer's (BCS) theory of superconductivity, the usual metallic parabolic nearly-free-electron band is modified by opening a gap at the Fermi level. The electronic density of states is zero within the gap and presents peaks at the gap edges. Many materials have superconducting properties that deviate from BCS theory and, as a consequence, the density of states is very different, too. The differently shaped density of states signals new paradigms in superconductivity, such as two-band, anisotropic, or multigap superconductivity. Here, measurements of the density of states obtained using Scanning tunneling microscopy (STM) in representative compounds are reviewed and future prospects of advances in superconductivity using STM are discussed.