For the first time, University of Basel researchers have equipped an
ultrathin semiconductor with superconducting contacts. These extremely thin
materials with novel electronic and optical properties could pave the way
for previously unimagined applications. Combined with superconductors, they
are expected to give rise to new quantum phenomena and find use in quantum
technology.
Whether in smartphones, televisions or building technology, semiconductors
play a central role in electronics and therefore in our everyday lives. In
contrast to metals, it is possible to adjust their electrical conductivity
by applying a voltage and hence to switch the current flow on and off.
With a view to future applications in electronics and quantum technology,
researchers are focusing on the development of new components that consist
of a single layer (monolayer) of a semiconducting material. Some naturally
occurring materials with semiconducting properties feature monolayers of
this kind, stacked to form a three-dimensional crystal. In the laboratory,
researchers can separate these layers – which are no thicker than a single
molecule – and use them to build electronic components.
New properties and phenomena
These ultrathin semiconductors promise to deliver unique characteristics
that are otherwise very difficult to control, such as the use of electric
fields to influence the magnetic moments of the electrons. In addition,
complex quantum mechanical phenomena take place in these semiconducting
monolayers that may have applications in quantum technology.
Scientists worldwide are investigating how these thin semiconductors can be
stacked to form new synthetic materials, known as van der Waals
heterostructures. However, until now, they have not succeeded in combining
such a monolayer with superconducting contacts in order to dig deeper into
the properties and peculiarities of the new materials.
Superconducting contacts
A team of physicists, led by Dr. Andreas Baumgartner in the research group
of Professor Christian Schönenberger at the Swiss Nanoscience Institute and
the Department of Physics of the University of Basel, has now fitted a
monolayer of the semiconductor molybdenum disulfide with superconducting
contacts for the first time. (see box)
The reason why this combination of semiconductor and superconductor is so
interesting is that the experts expect components of this kind to exhibit
new properties and physical phenomena. “In a superconductor, the electrons
arrange themselves into pairs, like partners in a dance – with weird and
wonderful consequences, such as the flow of the electrical current without a
resistance,” explains Baumgartner, the project manager of the study. “In the
semiconductor molybdenum disulfide, on the other hand, the electrons perform
a completely different dance, a strange solo routine that also incorporates
their magnetic moments. Now we would like to find out which new and exotic
dances the electrons agree upon if we combine these materials.”
Suitable for use as a platform
The electrical measurements at the low temperatures required for
superconductivity – just above absolute zero (-273.15°C) – show clearly the
effects caused by the superconductor; for example, at certain energies,
single electrons are no longer allowed. Moreover, the researchers found
indications of a strong coupling between the semiconductor layer and the
superconductor.
“Strong coupling is a key element in the new and exciting physical phenomena
that we expect to see in such van der Waals heterostructures, but were never
able to demonstrate,” says Mehdi Ramezani, lead author of the study.
“And, of course, we always hope for new applications in electronics and
quantum technology,” says Baumgartner. “In principle, the vertical contacts
we’ve developed for the semiconductor layers can be applied to a large
number of semiconductors. Our measurements show that these hybrid monolayer
semiconductor components are indeed possible –perhaps even with other, more
exotic contact materials that would pave the way for further insights,” he
adds.
Reference:
“Superconducting Contacts to a Monolayer Semiconductor” by Mehdi Ramezani,
Ian Correa Sampaio, Kenji Watanabe, Takashi Taniguchi, Christian
Schönenberger and Andreas Baumgartner, 23 June 2021, Nano Letters.