Researchers have made a remarkable advancement in creating next-generation carbon-based quantum materials, paving the way for progress in quantum electronics. This breakthrough involves a new kind of graphene nanoribbon (GNR), called Janus GNR (JGNR). What makes this material stand out is its distinctive zigzag edge, which features a unique ferromagnetic edge state on one side. This interesting configuration allows for the formation of a one-dimensional ferromagnetic spin chain, potentially important for applications in quantum electronics and quantum computing.
A team of researchers from the National University of Singapore (NUS) has made a significant breakthrough in developing advanced carbon-based quantum materials, heralding new advancements in quantum electronics.
They have introduced a new type of graphene nanoribbon (GNR) known as Janus GNR (JGNR). This material is characterized by its unique zigzag edge and a specific ferromagnetic edge state found on one of its sides. This innovative structure allows for the creation of one-dimensional ferromagnetic spin chains, which hold great potential for use in quantum electronics and quantum computing.
The research was spearheaded by Associate Professor Lu Jiong and his team from the NUS Department of Chemistry, with support from international collaborators.
Graphene nanoribbons, which are narrow strips made of nanoscale honeycomb carbon, display exceptional magnetic characteristics due to the behavior of unpaired electrons in their π-orbitals. By meticulously engineering the edges into a zigzag pattern, researchers can create a one-dimensional spin-polarized channel. This capability presents significant opportunities for applications in spintronic devices and developing advanced multi-qubit systems, which are essential for quantum computing.
The term “Janus,” named after the ancient Roman god who symbolizes beginnings and endings, aptly describes materials with distinct characteristics on opposite sides. In the case of JGNR, it boasts a unique structure where only one edge possesses a zigzag pattern, making it the first-ever one-dimensional ferromagnetic carbon chain. This innovative design is accomplished by using a Z-shaped precursor that generates a regular array of hexagonal carbon rings on one zigzag edge, disrupting the structural and spin symmetry of the ribbon.
According to Assoc Prof Lu, “Magnetic graphene nanoribbons—thin strips of graphene formed from interconnected benzene rings—hold immense promise for quantum technologies, given their long spin coherence times and the ability to function at room temperature. Crafting a one-dimensional single zigzag edge in these systems is both challenging and crucial for the bottom-up assembly of multiple spin qubits essential for quantum technologies.”
This major milestone resulted from extensive collaboration among synthetic chemists, materials scientists, and theoretical physicists, including contributions from Professor Steven G Louie at UC Berkeley in the U.S., Professor Hiroshi Sakaguchi from Kyoto University in Japan, and others.
The research findings were published in the scientific journal Nature on January 9, 2025.
Process of Creating Janus Graphene Nanoribbons
To manufacture the JGNR, the researchers first designed and synthesized a set of unique ‘Z-shape’ molecular precursors using conventional solution chemistry methods. These precursors were then utilized for an on-surface synthesis process, a novel solid-phase chemical reaction conducted in an ultra-clean environment. This method enabled the researchers to precisely control the atomic structure and shape of the graphene nanoribbons.
The ‘Z-shape’ configuration permits asymmetric fabrication by modifying one of the two branches independently, thus creating a targeted ‘defective’ edge while keeping the other zigzag edge intact. Additionally, varying the length of the modified branch allows for adjustments to the width of the JGNRs. Characterization through advanced scanning probe microscopy/spectroscopy and first-principles density functional theory has validated the successful creation of JGNRs with a ferromagnetic ground state localized solely along the single zigzag edge.
“The thoughtful design and on-surface synthesis of this new class of JGNRs represent a significant conceptual and experimental achievement in realizing one-dimensional ferromagnetic chains. Developing these JGNRs not only broadens the opportunities for meticulous engineering of exotic quantum magnetism but also facilitates the creation of stable spin arrays to be used as next-generation qubits. Moreover, it allows for the manufacturing of one-dimensional spin-polarized transport channels with adjustable bandgaps, which could propel carbon-based spintronics into an advanced one-dimensional realm,” noted Assoc Prof Lu.
