Two-level Physics in a Model Metallic Break Junction

TL;DR

This paper models a metal break-junction at its breaking point, using a two-level system to analyze how atomic motion affects conductance, revealing fractional zero-temperature conductance that diminishes with temperature.

Contribution

It introduces a novel two-level system model for atomic motion in a break-junction and combines NRG with conformal field theory to analyze conductance behavior.

Findings

Conductance remains finite and fractional at zero temperature.

Conductance decreases rapidly as temperature increases.

Model aligns with conformal field theory predictions.

Abstract

We consider a model inspired by a metal break-junction hypothetically caught at its breaking point, where the non-adiabatic center-of-mass motion of the bridging atom can be treated as a two-level system. By means of Numerical Renormalization Group (NRG) we calculate the influence of the two level system on the ballistic conductance across the bridge atom. The results are shown to be fully consistent with a conformal field theory treatment. We find that the conductance, calculated by coupling Fermi liquid theory to our NRG is always finite and fractional at zero temperature, but drops quite fast as the temperature increases.