The Heart of Fidelity

TL;DR

This paper demonstrates that for large symmetric Friedel-Anderson impurities, the wave function change upon volume doubling can be universally described by a single-electron state at the Fermi level, independent of impurity parameters.

Contribution

It introduces a universal single-electron state that describes wave function changes in large symmetric impurities, unifying Kondo and Friedel impurity cases.

Findings

Wave function change is described by a universal state |q>

Universal state is independent of impurity parameters

Applicable when level spacing is smaller than resonance width

Abstract

The multi-electron wave function of an interacting electron system depends on the size of the system, i.e. the number of electrons. Here the question investigated is how the wave function changes for a symmetric Friedel-Anderson impurity when the volume is doubled. It turns out that for sufficiently large volume (when the level spacing is smaller than the resonance width) the change in the wave function can be expressed in terms of a universal single-electron state |q> centered at the Fermi level. This electron state is independent of the number of electrons and independent of the parameters of the Friedel-Anderson impurity. It is even the same universal state for a Kondo impurity and a symmetric Friedel impurity independent of any parameter. The only requirement is that the impurity has a resonance exactly at the Fermi level and that the level spacing is smaller than the resonance width. This result clarifies recent fidelity calculations.