NUS Navigating the Quantum Realm: Butterfly Nanographene

In a groundbreaking development, researchers from the National University of Singapore (NUS) have unveiled a revolutionary design concept for next-generation carbon-based quantum materials. Led by Associate Professor Lu Jiong from the NUS Department of Chemistry and Institute for Functional Intelligent Materials, in collaboration with Professor Wu Jishan and international counterparts, the team has engineered a magnetic nanographene with a unique butterfly-shaped structure, hosting highly correlated spins.

This innovation holds tremendous promise for propelling the advancement of quantum materials, critical for the evolution of cutting-edge quantum computing technologies set to redefine information processing and high-density storage capabilities.

Nanographene, constructed from graphene molecules, boasts exceptional magnetic properties owing to the distinct behaviour of specific electrons in the carbon atoms’ π-orbitals. By intricately designing the arrangement of these carbon atoms at the nanoscale, precise control over the behaviour of these unique electrons is achievable. This renders nanographene an immensely viable candidate for crafting minute magnets and fabricating fundamental building blocks essential for quantum computers, known as quantum bits or qubits.

The butterfly-shaped magnetic graphene, an outcome of the meticulous atomic-precise design of the π-electron network within nanostructured graphene, features four rounded triangles resembling butterfly wings. Each wing harbours an unpaired π-electron, pivotal for the observed magnetic properties.

Assoc Prof Lu explained, “Creating multiple highly entangled spins in such systems is a daunting yet essential task for building scalable and complex quantum networks.”

This feat, achieved through interdisciplinary collaboration among synthetic chemists, materials scientists, and physicists, signifies a significant stride in quantum materials research.

Published in the prestigious scientific journal Nature Chemistry on February 19, 2024, this breakthrough heralds a new era in the realm of quantum materials, offering unparalleled potential for the development of advanced quantum computing technologies.

Conventionally, the magnetic properties of nanographene are predominantly derived from the arrangement of its π-electrons or the strength of their interactions. However, orchestrating these properties to engender multiple correlated spins has remained a formidable challenge. Additionally, nanographene typically exhibits a singular magnetic order, wherein spins align either ferromagnetically or antiferromagnetically.

To surmount these obstacles, the researchers devised a groundbreaking method. Their butterfly-shaped nanographene, showcasing both ferromagnetic and antiferromagnetic properties, is crafted by amalgamating four smaller triangles into a rhombus at its core. Measuring approximately 3 nanometres in size, this nanographene represents a paradigm shift in quantum materials design and synthesis.

To produce the butterfly nanographene, researchers initially designed a specialised molecule precursor via conventional in-solution chemistry. Subsequently, this precursor underwent on-surface synthesis, a novel solid-phase chemical reaction conducted in a vacuum environment. This approach afforded precise control over the nanographene’s shape and structure at the atomic level, marking a significant breakthrough in nanomaterials fabrication.

An intriguing aspect of the butterfly nanographene lies in its four unpaired π-electrons, with spins primarily delocalised in the wing regions and entangled together. Utilising an ultra-cold scanning probe microscope with a nickelocene tip as an atomic-scale spin sensor, researchers measured the magnetism of the butterfly nanographene.

This pioneering technique not only enables the probing of entangled spins but also elucidates nanographene’s magnetism at the atomic scale, unlocking new avenues for manipulating magnetic properties at the smallest scale and advancing quantum materials research.

Assoc Prof Lu expressed optimism for the future, stating, “The insights gained from this study pave the way for creating new-generation organic quantum materials with designer quantum spin architectures. Our goal is to measure the spin dynamics and coherence time at the single-molecule level, representing a significant stride towards achieving more powerful information processing and storage capabilities.”