Physicists at the University of the Witwatersrand in Johannesburg have proven that diamonds contain an extremely rare, yet efficient form of superconductivity that until now has only been known to occur in one or two other materials, and only theoretically in diamonds.
Diamonds have a firm foothold in our lexicon. Their many properties
often serve as superlatives for quality, clarity and hardiness. Aside
from the popularity of this rare material in ornamental and decorative
use, these precious stones are also highly valued
in industry where they are used to cut and polish other hard materials
and build radiation detectors.
More than a decade ago, a new property was uncovered in diamonds when
high concentrations of boron are introduced to it – superconductivity.
Superconductivity occurs when two electrons with opposite spin form a
pair (called a Cooper pair), resulting in the
electrical resistance of the material being zero. This means a large
supercurrent can flow in the material, bringing with it the potential
for advanced technological applications. Yet, little work has been done
since to investigate and characterise the nature
of a diamond’s superconductivity and therefore its potential
applications.
New research led by Professor Somnath Bhattacharyya in the Nano-Scale Transport Physics Laboratory (NSTPL) in the School
of Physics at the University of the Witwatersrand
in Johannesburg, South Africa, details the phenomenon of
what is called “triplet superconductivity” in diamond. Triplet
superconductivity occurs when electrons move in a composite spin state
rather than as a single pair.
“In a conventional superconducting material such as aluminium,
superconductivity is destroyed by magnetic fields and magnetic
impurities, however triplet superconductivity in a diamond can exist
even when combined with magnetic materials. This leads to more
efficient and multifunctional operation of the material,” explains
Bhattacharyya.
The team’s work has recently been published in an article in the New Journal of Physics,
titled “Effects of
Rashba-spin-orbit coupling on superconducting boron-doped
nanocrystalline diamond films: evidence of interfacial triplet
superconductivity”.
This research was done in collaboration with Oxford University
(UK) and Diamond Light Source (UK). Through these collaborations,
beautiful atomic arrangement of diamond crystals and interfaces that
have never been seen before could be visualised, supporting
the first claims of ‘triplet’ superconductivity.
Practical proof of triplet superconductivity in diamonds came with
much excitement for Bhattacharyya and his team. “We were even working on
Christmas day, we were so excited,” says Davie Mtsuko. “This is
something that has never been before been claimed
in diamond,” adds Christopher Coleman. Both Mtsuko and Coleman are
co-authors of the paper.
Despite diamonds’ reputation as a highly rare and expensive resource,
they can be manufactured in a laboratory using a specialised piece of
equipment called a vapour deposition chamber. The Wits NSTPL has
developed their own plasma deposition chamber which
allows them to grow diamonds of a higher than normal quality – making
them ideal for this kind of advanced research.
This finding expands the potential uses of diamond, which is already
well-regarded as a quantum material. “All conventional technology is
based on semiconductors associated with electron charge. Thus far, we
have a decent understanding of how they interact,
and how to control them. But when we have control over quantum states
such as superconductivity and entanglement, there is a lot more physics
to the charge and spin of electrons, and this also comes with new
properties,” says Bhattacharyya. “With the new surge
of superconducting materials such as diamond, traditional silicon
technology can be replaced by cost effective and low power consumption
solutions”.
The induction of triplet superconductivity in diamond is important
for more than just its potential applications. It speaks to our
fundamental understanding of physics. “Thus far, triplet
superconductivity exists mostly in theory, and our study gives us
an opportunity to test these models in a practical way,” says
Bhattacharyya.
