For The First Time Ultrathin Semiconductors Equipped With Superconducting Contacts

For the first time, scientists from the University of Basel have implemented ultrathin semiconductors with superconducting contacts. These are very thin elements with novel optical and electronic features that could pave the way for earlier unimagined applications. Linked with superconductors, they are assumed to provide growth to novel quantum events and find application in quantum technology.

Whether in televisions, smartphones, or Smart-home technology, semiconductors play a prime role in electronics and therefore in our daily lives. In contrast to alloys, it is feasible to set their electrical conductivity by applying a voltage and hence to change the current flow on and off.

Ultrathin Semiconductors
Between the two protective layers of boron nitride (hBN), a single layer of molybdenum disulfide (MoS2) is sandwiched, with molybdenum rhenium (MoRe) contacts extending through the upper one. For electrical control, graphene (gate) is applied. Source: Mehdi Ramezani, Swiss Nanoscience Institute, University of Basel

With a prospect to future demands in electronics and quantum technology, scientists are concentrating on the advancement of components that consist of a single layer (monolayer) of semiconducting material. Some naturally occurring materials with semiconducting characteristics feature monolayers of this type, accumulated to form a three-dimensional crystal. In the laboratory, scientists can isolate these layers – which are no thicker than a single molecule – and utilize them to develop electronic components.

New Features and Phenomena

These ultrathin semiconductors guarantee to deliver unique characteristics that are otherwise very challenging to manage, such as the use of electric fields to control the magnetic moments of the electrons. Furthermore, the complex quantum mechanical process takes place in these semiconducting monolayers that may have applications in quantum technology.

For the first time, SNI researchers (University of Basel) have equipped anatomically ultrathin semiconductors with superconducting contacts. In this video, they show the elaborate fabrication process. Credit: C. Möller and M. Ramezani, Swiss Nanoscience Institute, University of Basel

Researchers from all around the globe are examining how these thin semiconductors can be stacked to produce unique synthetic materials, known as van der Waals heterostructures. Though, until now, they have not succeeded in linking such a monolayer with superconducting contacts to dig deeper into the characteristics and singularities of the new materials.

Superconducting Contacts

A group of scientists, headed by Dr. Andreas Baumgartner in the study team of Professor Christian Schönenberger at the Department of Physics of the University of Basel and the Swiss Nanoscience Institute, 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 superconductor and semiconductor is so exciting is that the experts anticipate components of this type to show new features and physical phenomena. “In a superconductor, the electrons organize themselves into sets, like partners in a dance – with weird and amazing outcomes, such as the flow of the electrical current without a resistance,” explains Baumgartner, the project director of the research. “In the semiconductor molybdenum disulfide, on the other hand, the electrons perform an entirely diverse dance, a rare solo routine that also includes their magnetic moments. Now we would like to discover out which unique and exotic dances the electrons accept if we connect these materials.”

Suitable For Use as a Platform

The electrical analyses at the low temperatures needed for superconductivity – just above absolute zero (-273.15°C) – show clearly the effects induced by the superconductor; for example, at specific energies, single electrons are no longer permitted. Moreover, the scientists observed signs of effective coupling between the superconductor and the semiconductor layer.

“Effective coupling is an essential part in the unique and exciting physical phenomena that we anticipate to see in such van der Waals heterostructures, but were never able to demonstrate,” says Mehdi Ramezani, lead author of the research.

“And, of course, we constantly seek for new uses in quantum technology and electronics,” says Baumgartner. “In principle, the vertical contacts we’ve created for the semiconductor layers can be implemented to a large number of semiconductors. Our analyses confirm that these hybrid monolayer semiconductor elements are certainly possible –perhaps even with other, more exotic contact materials that would pave the way for further insights,” he adds.

Journal Reference: “Superconducting Contacts to a Monolayer Semiconductor” by Mehdi Ramezani, Kenji Watanabe, Takashi Taniguchi, Christian Schönenberger, Ian Correa Sampaio, and Andreas Baumgartner, 23 June 2021, Nano Letters.

DOI: 10.1021/acs.nanolett.1c00615

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