In a strange turn of quantum materials research, researchers were able to fabricate a material that exhibits both superconductivity and quantum Hall effect - two phenomena that are generally seen as opposites as far as electrical resistance is concerned.
The newly fabricated material, based on nitride-based raw materials, concurrently exhibits superconductivity - the state of zero electrical resistance - and quantum Hall effect, which refers to the precise generation of electrical resistance when a magnetic field is introduced. Details of the new study, led by scientists from Cornell University, are published in the journal Science Advances.
Two Electrical Resistance Extremes in the Same Material
"This is a beautiful marriage of the two things we know, at the microscale, that give electrons the most startling quantum properties," shares Debdeep Jena, the David E. Burr Professor of Engineering at Cornell's School and Electrical and Computer Engineering and in the university's department of Materials Science and Engineering. Jena led the study, together with doctoral candidate Philip Dang and research associate Guru Khalsa, with the three being senior authors for the paper.
They also explained in a press release from Cornell that the perception of superconductivity and quantum Hall effect being opposites stems from the fact that magnetic fields have an adverse effect on superconductivity in materials. He adds, however, that the quantum Hall effect is mostly only present in semiconductors at extremely large magnetic fields, leading their team to "play with these two extremes."
"Researchers in the past few years have been trying to identify materials which show both properties with mixed success," Jena added.
Tapping Into The Nitride Potential For New Sciences
With the new material from Cornell's Jena-Xing Laboratory, researchers were able to demonstrate the potential of nitride materials. Nitrides - basically nitrogen compounds where N has a formal oxidation state of negative three (-3) - have found wide use in the manufacture of LED lamps and electronic components, such as transistors such as smartphones and home lighting. However, its basic properties might have led the scientific community to overlook its potential in the more advanced fields of quantum computing and cryogenic electronics - or electronic behavior under extremely low temperature environments.
"The material itself is not as perfect as silicon, meaning it has a lot more defects," explains Huli Grace Xing, co-author in the study and a William L. Quackenbush Professor of Electrical and Computer Engineering and of Materials Science and Engineering. She adds that on the other hand, the material's robust nature has "thrown pleasant surprises to the research community," even despite its structural irregularities compared to, say, semiconductor materials.
"There may be a path forward for us to truly integrate different modalities of quantum computing - computation, memory, communication," Xing added.
In the new superconductor - quantum Hall effect material, researchers engineered epitaxial nitride heterostructures, which are atomically thin layers of niobium nitride and gallium nitride. They started looking for situations of magnetic fields and temperatures that would allow the material laters to retain both their quantum Hall and superconductivity properties.
With help from colleagues at the Naval Research Laboratory, researchers eventually found a narrow range where the materials exhibited both properties.
"I think the flexibility of the nitrides really opens up new possibilities and ways to explore topological states of matter." said Guru Khalsa, one of the senior authors of the paper.
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