Local Friedel sum rule on graphs

TL;DR

This paper explores the relationship between the scattering matrix and local density of states on quantum graphs, extending the Friedel sum rule to include local and discrete spectral features.

Contribution

It introduces a local Friedel sum rule on graphs that relates scattering data to local density of states, including discrete spectrum considerations.

Findings

Derived relations between scattering matrix and local density of states.

Demonstrated the theory with simple graph examples.

Extended Friedel sum rule to include discrete spectrum on graphs.

Abstract

We consider graphs made of one-dimensional wires connected at vertices and on which may live a scalar potential. We are interested in a scattering situation where the graph is connected to infinite leads. We investigate relations between the scattering matrix and the continuous part of the local density of states, the injectivities, emissivities and partial local density of states. Those latter quantities can be obtained by attaching an extra lead at the point of interest and by investigating the transport in the limit of zero transmission into the additional lead. In addition to the continuous part related to the scattering states, the spectrum of graphs may present a discrete part related to states that remain uncoupled to the external leads. The theory is illustrated with the help of a few simple examples.