Editorial Feature

Phosphorene: Superconductive Atomically Thin 2D Material

Image credit: University of Manchester

Scientists from Manchester University show that phosphorene is superconductive when electrons are supplied by intercalated alkali metal atoms. Unlike for graphene, the type of intercalating alkali atom did not matter – the observed superconductivity was universal. 

Phosphorene is a single layer of black phosphorous – just as graphene is a single layer of graphite. And just as graphene, phosphorene is a similarly exciting 2D material with many remarkable electrical and optical properties.

For example, theoretical predictions have indicated that its parent material, black phosphorous, may be superconductive, which means that it may conduct electricity without any resistance. This property is utilised in magnets for MRI scanners and levitating trains amongst other things.

Experimentally, superconductivity has so far only been achieved in black phosphorous by applying huge pressure to the material.

Though, in the strict sense, the pressurised material was no longer black phosphorous but another form of phosphorous. Whether superconductivity can be observed in black phosphorous without applying pressure has so far remained unanswered.

First experimental evidence of phosphorene superconductivity

Now a research team from Manchester University, led by professor Irina Grigorieva, demonstrated for the first time that phosphorene can become superconductive if supplied with sufficient electrons. Such superconductors that are only an atom thick are sought-after for miniature devices.

Apart from applications, scientists are also interested in knowing the limits of superconductivity, which the findings, published in the journal Nature Communications, contributes to [1].

Until a decade ago, superconductivity was only known in bulk materials but in the beginning of this year, it was shown that the 2D material graphene can be superconductive [2].

Generally, superconductivity is found in materials when they have sufficient electrons available that can interact with each other.

Intercalation with different alkali atoms yields universal superconductivity

The scientists from Manchester achieved this in phosphorene by intercalating atoms of alkali metals in black phosphorous. In other words, they incorporated the atoms between the phosphorene layers.

Looking at the properties of the intercalated black phosphorous they found that it did not matter which alkali metal they used for intercalation. This indicates that the superconductivity can be entirely attributed to phosphorene.

Because phosphorene and black phosphorous are similar to graphene and graphite, this is an unforeseen finding. As for graphene “we expected that each electron-donating metal will produce a different superconductor”, explains Renyang Zhang, a graduate student in charge of the experimental work.

He adds “But to our surprise, all metal donors produce exactly the same superconducting material, with identical properties.”

Superconductive atomically thin materials for miniature devices

Grigorieva comments “Nothing like this was known before.” The unusual superconductivity behaviour calls for further investigation because some more fundamental effects might play a role.  One thing is certain: the discovery brings atomically thin materials one step further towards applications in electronics and quantum technologies.

References:

[1] R. Zhang et al. (2017) Intercalant-independent transition temperature in superconducting black phosphorus. Nature Communications 8:15036. DOI: 10.1038/ncomms15036.

[2] A. Di Bernardo et al. (2017) p-wave triggered superconductivity in single-layer graphene on an electron-doped oxide superconductor. Nature Communications 8:14024. DOI: 10.1038/ncomms14024.

[3] Phys.org (2017) Phosphorene reveals its superconductivity. Available at: https://phys.org/news/2017-04-phosphorene-reveals-superconductivity.html?utm_source=nwletter&utm_medium=email&utm_campaign=daily-nwletter (assessed 13/04/2017)  

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