A graphene layer lets an ultrathin superconductor grow uniformly while protecting it from oxidation outside controlled environments.
MIT researchers have developed an ultrathin superconductor that can be produced over large areas and remain stable in air, potentially enabling smaller and more scalable quantum devices.
The material, niobium diselenide, is only around one nanometre thick. Although it has promising superconducting properties, it typically oxidises and degrades almost immediately upon exposure to air.
Researchers addressed the problem by placing graphene on a silicon dioxide substrate before growing the superconductor. Chemical precursors enter the narrow gap between the layers, where the niobium diselenide forms beneath the graphene.
The graphene protects the material from oxidation while guiding it into a smooth, continuous monolayer. Using the technique, the team produced a layer more than an inch across, rather than the tiny flakes typically obtained through conventional methods.
Researchers then developed an oxidation-free transfer process and integrated the material into a superconducting microwave circuit. It retained its superconducting behaviour after fabrication and exhibited high kinetic inductance.
High kinetic inductance allows substantial inductive energy to be stored within a small area. Quantum circuits currently achieve similar effects using arrays of Josephson junctions, which require considerably more space.
Replacing such arrays with a small piece of ultrathin superconducting material could help miniaturise superconducting quantum hardware and technologies, including highly sensitive quantum detectors.
The growth technique is not limited to niobium diselenide. Researchers demonstrated that it could be extended to other atomically thin quantum materials with different potentially useful properties.
The work involved MIT and collaborators from several universities and laboratories and was published in Nature. Researchers now plan to integrate the material into functional quantum-device architectures and investigate its underlying physics and practical applications.
Why does it matter?
Producing an air-stable ultrathin superconductor over a large area removes an important obstacle to studying and manufacturing two-dimensional quantum materials. The experiment does not yet demonstrate a complete miniaturised quantum device. Still, it could provide a route towards more compact circuits and scalable quantum technologies if the material performs reliably in functional architectures.
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