Quantum transport transition from quantum interference to Coulomb blockade in suspended CVD graphene nanoribbons with reduced ribbon widths

Quantum transport in graphene nanoribbons (GNRs) is essential for advancing electronic and quantum device applications. In particular, the Coulomb blockade effect in GNR-based devices holds promise for quantum computing, single-electron transistors, and highly sensitive charge detectors. To investigate electron transport characteristics at the nanoscale, we synthesized and tailored suspended CVD graphene nanoribbons with widths ranging from 705 nm to 50 nm and lengths of approximately 150 nm. While bottom-up synthesis offers precise control over edge structure, tailoring graphene into narrower strips significantly enhances edge disorder and quantum confinement effects. Our study focuses on fabricated GNRs with sub-100 nm widths to explore quantum interference-induced localization and Coulomb blockade phenomena. We observe a transition in transport behavior from magnetoresistance fluctuations associated with quantum interference effects---such as weak localization and universal conductance fluctuations (UCF)---to single-electron transport, characterized by Coulomb blockade effects. Notably, Coulomb blockade behavior is particularly evident in narrow nanoribbons (50 nm width), as seen in diamondlike structures in source-drain voltage versus back-gate voltage characteristics. The phase coherence length, extracted using weak localization theory, varies from 60 nm to 220 nm as the ribbon width is reduced from 700 nm to 50 nm at 2 K. Importantly, our findings indicate that nanoscale GNRs exhibit Coulomb blockade behavior due to enhanced ribbon disorder and edge roughness. These results provide valuable insights into quantum transport mechanisms in graphene nanoribbons and offer significant advantages for the design and application of graphene-based electronic and quantum devices.