Absence of magnetically-induced fractional quantization in atomic contacts

TL;DR

This study investigates atomic contacts of magnetic and non-magnetic metals using break junctions, finding no evidence of fractional conductance quantization even under magnetic fields, and highlighting the role of gas molecules in observed conductance features.

Contribution

The paper provides experimental evidence that magnetic atomic contacts do not exhibit fractional conductance quantization, challenging previous claims and supporting recent theoretical models.

Findings

No fractional conductance quantization observed in pure metals.

Gas molecules induce features resembling fractional quantization.

Current is not fully polarized in the studied metals.

Abstract

Using the mechanically controlled break junction technique at low temperatures and under cryogenic vacuum conditions we have studied atomic contacts of several magnetic (Fe, Co and Ni) and non-magnetic (Pt) metals, which recently were claimed to show fractional conductance quantization. In the case of pure metals we see no quantization of the conductance nor half-quantization, even when high magnetic fields are applied. On the other hand, features in the conductance similar to (fractional) quantization are observed when the contact is exposed to gas molecules. Furthermore, the absence of fractional quantization when the contact is bridged by H_2 indicates the current is never fully polarized for the metals studied here. Our results are in agreement with recent model calculations.