Ultra-thin semiconductors electrically connected to superconductors for the first time – Eurasia Review

For the first time, researchers at the University of Basel have equipped an ultrathin semiconductor with superconducting contacts. These extremely thin materials with new electronic and optical properties could pave the way for previously unimaginable applications. Combined with superconductors, they should give rise to new quantum phenomena and find their use in quantum technology.

Whether in smartphones, televisions or building technology, semiconductors play a central role in electronics and therefore in our daily life. Unlike metals, it is possible to adjust their electrical conductivity by applying a voltage and thus turn 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 made of a single layer (monolayer) of a semiconductor material. Some natural materials with semiconductor properties have such monolayers stacked together to form a three-dimensional crystal. In the lab, 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 ultra-thin semiconductors promise to provide unique characteristics that are otherwise very difficult to control, such as the use of electric fields to influence the magnetic moments of electrons. In addition, complex quantum mechanical phenomena take place in these semiconductor monolayers which may have applications in quantum technology.

Scientists around the world are studying how these thin semiconductors can be stacked together to form new synthetic materials, known as van der Waals heterostructures. However, so far they have failed to combine such a monolayer with superconducting contacts in order to deepen the properties and peculiarities of new materials.

Superconducting contacts

A team of physicists, led by Dr Andreas Baumgartner in the research group of Professor Christian Schönenberger at the Swiss Institute for Nanoscience and the Department of Physics at the University of Basel, has now equipped a semi-molybdenum disulfide monolayer. conductor with superconducting contacts for the first time. (see box)

The reason why this combination of semiconductor and superconductor is so interesting is that experts expect components of this type to exhibit new properties and new physical phenomena. “In a superconductor, electrons organize themselves in pairs, like partners in a dance – with strange and wonderful consequences, such as the passage of electric current without resistance,” says Baumgartner, the study’s project leader. “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 tune in if we combine these materials. “

Suitable for use as a platform

Electrical measurements at the low temperatures required for superconductivity – just above absolute zero (-273.15 ° C) – clearly show the effects caused by the superconductor; for example, at certain energies, single electrons are no longer allowed. In addition, 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 which we have never been able to demonstrate,” said Mehdi Ramezani, lead author of the ‘study.

“And, of course, we are always hoping for new applications in electronics and quantum technology,” says Baumgartner. “In principle, the vertical contacts that we have developed for semiconductor layers can be applied to a large number of semiconductors. Our measurements show that these hybrid single-layer semiconductor components are indeed possible, perhaps even with other more exotic contact materials that would pave the way for further information, ”he adds.

Elaborate manufacturing process

Manufacturing the new component into one type of sandwich made from different materials requires a large number of different steps. At each stage, it is important to avoid contamination, as it seriously affects the transport of electric charges.

To protect the semiconductor, the researchers place a monolayer of molybdenum disulfide between two thin layers of boron nitride, through which they previously etched the contacts vertically by electron beam lithography and ion etching. They then deposit a thin layer of rhenium molybdenum as a contact material – a material that retains its superconducting properties even in the presence of strong magnetic fields.

Working under a protective nitrogen atmosphere in a glove box, the researchers stack the boron nitride layer on top of the molybdenum disulfide layer and combine the underside with another layer of boron nitride as well as a layer of graphene. for electrical control. The researchers then place this elaborate van der Waals heterostructure on a silicon / silicon dioxide wafer.