Investigation on the reported superconductivity in intercalated black phosphorus

TL;DR

This study questions the intrinsic superconductivity in intercalated black phosphorus, demonstrating that observed superconductivity is likely due to residual tin contamination rather than the material itself.

Contribution

The paper provides evidence that previously reported superconductivity in intercalated black phosphorus is caused by tin impurities, not intrinsic properties of the intercalated material.

Findings

Superconductivity at 3.8 K observed in Sn-contaminated BP crystals.

High-pressure prepared BP crystals without Sn show no superconductivity.

Sn contamination is responsible for the reported superconducting transition.

Abstract

Superconductivity intrinsic to the intercalated black phosphorus (BP) with a transition temperature Tc of 3.8 K, independent of the intercalant, whether an alkali or an alkaline earth element, has been reported recently by R. Zhang et al. (2017). However, the reported Tc and the field effect on the superconducting (SC) transition both bear great similarities to those for the pure Sn, which is commonly used for BP synthesis under the vapor transport method. We have therefore decided to determine whether a minute amount of Sn is present in the starting high purity BP crystals and whether it is the culprit for the small SC signal detected. Energy-dispersive X-ray spectroscopy results confirmed the existence of Sn in the starting high purity BP crystals purchased from the same company as in R. Zhang et al. (2017). We have reproduced the SC transition at 3.8 K in Li- and Na-intercalated BP crystals that contain minute amounts of Sn when prepared by the vapor transport method but not in BP crystals that are free of Sn when prepared by the high-pressure method. We have therefore concluded that the SC transition reported by R. Zhang et al. (2017) is associated with the Sn but not intrinsic to the intercalated BP crystals.