Topological quantum phase transition of nickelocene on Cu(100)

TL;DR

This paper reports the experimental observation of a topological quantum phase transition in a nickelocene molecule on Cu(100), revealing a transition from a local Fermi liquid to a non-Landau Fermi liquid driven by Kondo correlations.

Contribution

It provides the first experimental evidence of a topological quantum phase transition in a magnetic nanosystem, modeled as a two-orbital Anderson impurity with anisotropy.

Findings

Observation of a transition from high to low conductance states

Identification of a non-trivial quantized Luttinger integral

Explanation of behavior variations due to valence, temperature, and structural relaxation

Abstract

Local quantum phase transitions driven by Kondo correlations have been theoretically proposed in several magnetic nanosystems; however, clear experimental signatures are scant. Modeling a nickelocene molecule on a Cu(100) substrate as a two-orbital Anderson impurity with single-ion easy-plane anisotropy coupled to two conduction bands, we find that recent scanning tunneling spectra measured at different microscope tip heights reveal the existence of a topological quantum phase transition from the usual local Fermi liquid with high zero-bias conductance to a non-Landau Fermi liquid, characterized by a non-trivial quantized Luttinger integral, with a small conductance. The effects of intermediate valence, finite temperature, and structural relaxation of the molecule position allow us to explain the different observed behaviors.