February 26, 2024

Material combination could support unique superconductivity for quantum computing

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A new fusion of materials, each with special electrical properties, has all the components needed for a unique type of superconductivity that could provide the basis for more robust quantum computing. The new combination of materials, created by a team led by Penn State researchers, could also provide a platform to explore physical behaviors similar to those of mysterious theoretical particles known as chiral Majoranas, which could be another promising component for quantum computing.

The new study appears in the journal Science. The work describes how the researchers combined the two magnetic materials in what they called a critical step toward realizing emerging interfacial superconductivity, which they are currently working on.

Superconductors – materials without electrical resistance – are widely used in digital circuits, powerful magnets in magnetic resonance imaging (MRI) and particle accelerators, as well as other technologies in which maximizing the flow of electricity is crucial.

When superconductors are combined with materials called magnetic topological insulators — thin films just a few atoms thick that have been made magnetic and restrict the movement of electrons to their edges — the new electrical properties of each component work together to produce “chiral topological superconductors.” .

Topology, or specialized geometries and symmetries of matter, generates unique electrical phenomena in the superconductor, which could facilitate the construction of topological quantum computers.

Quantum computers have the potential to perform complex calculations in a fraction of the time it takes traditional computers because, unlike traditional computers that store data as one or zero, the quantum bits in quantum computers simultaneously store data in a range of possible states.

Topological quantum computers further improve quantum computing by taking advantage of the way electrical properties are organized to make computers robust to decoherence, or the loss of information that occurs when a quantum system is not perfectly isolated.

“The creation of chiral topological superconductors is an important step toward topological quantum computing that can be scaled up for widespread use,” said Cui-Zu Chang, Henry W. Knerr Early Career Professor and associate professor of physics at Penn State and co-author of the paper.

“Chiral topological superconductivity requires three ingredients: superconductivity, ferromagnetism, and a property called topological order. In this study, we have produced a system with all three of these properties.”

The researchers used a technique called molecular beam epitaxy to stack a topological insulator that became magnetic and an iron chalcogenide (FeTe), a promising transition metal for harnessing superconductivity. The topological insulator is a ferromagnet – a type of magnet whose electrons rotate in the same way – while FeTe is an antiferromagnet, whose electrons rotate in alternating directions.

The researchers used a variety of imaging techniques and other methods to characterize the structure and electrical properties of the resulting combined material and confirmed the presence of all three critical components of chiral topological superconductivity at the interface between the materials.

Previous work in the area has focused on combining superconductors and non-magnetic topological insulators. According to the researchers, adding the ferromagnet has been particularly challenging.

“Normally, superconductivity and ferromagnetism compete with each other, so it is rare to find robust superconductivity in a ferromagnetic material system,” said Chao-Xing Liu, professor of physics at Penn State and co-corresponding author of the paper.

“But the superconductivity in this system is actually very robust against ferromagnetism. It would take a very strong magnetic field to remove the superconductivity.”

The research team is still exploring why superconductivity and ferromagnetism coexist in this system.

“It’s actually quite interesting because we have two magnetic materials that are not superconductors, but when we put them together and the interface between these two compounds produces very robust superconductivity,” Chang said.

“Iron chalcogenide is antiferromagnetic, and we predict its antiferromagnetic property to be weakened around the interface to give rise to emergent superconductivity, but we need more experiments and theoretical work to verify that this is true and to clarify the superconducting mechanism.”

The researchers said they believe this system will be useful in the search for material systems that exhibit behaviors similar to those of Majorana particles – theoretical subatomic particles first hypothesized in 1937. Majorana particles act as their own antiparticle, a unique property that could potentially allow them to be used as quantum bits in quantum computers.

“Providing experimental evidence for the existence of chiral Majorana will be a critical step in creating a topological quantum computer,” Chang said. “Our field has had a difficult past in trying to find these elusive particles, but we think this is a promising platform for exploring Majorana physics.”

More information:
Hemian Yi et al, Interface-induced superconductivity in magnetic topological insulators, Science (2024). DOI: 10.1126/science.adk1270. www.science.org/doi/10.1126/science.adk1270

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