Visualizing Quasi-Particle Scattering Resonances

The properties of superconductors can to a certain extent be understood within a framework of band theory, similar to the behavior of electrons in solids. However, as Atkinson and McDonald explain on page 57, the response of superconductors to disorder can differ widely from that expected from band theory. Conventional superconductors do not form bound states at defects, whereas unconventional superconductors do. Hudson et al. (page 88) have imaged resonances as a result of such bound states in such unconventional superconductors. Such direct imaging studies should improve our understanding of fundamental mechanisms underlying high-temperature superconductivity.