Fermi Edge Singularities: Boundstates and Finite Size Effects

Fermi edge adsorption singularities (FES) are studied using a combination of conformal field theory (CFT), an exact sum rule and numerical work on a tight binding model which is shown to exhibit remarkable simplifying features. The relationship between FES and Anderson orthogonality exponent is established in great generality, using CFT, including the case where the core hole potential produces a boundstate. Universal results on the adsorption intensity in a finite sized sample are obtained. Various predictions are checked numerically and the evolution of the adsorption intensity with electron density is studied.