Electron standing waves and the friedel oscillation

Defects and impurities situated in metals affect behavior of free electrons around them and induce modulated structures reflecting the wave nature of the electrons. The oscillatory spatial distribution of local density of states is called electron standing waves or quasi-particle interference pattern, whereas modulated electrostatic potential and charge density are the Friedel oscillation. In this review, we introduce real-space observation of these oscillatory structures by using scanning tunneling microscopy/spectroscopy (STM/S). Standing wave observations on surface states having spin structures induced by the Rashba effect, such as those of topological insulators, and the differences between the two confusing oscillatory structures will be discussed. (author)