Emergent electronic insulating states in a one-dimensional moir\'e superlattice
Two-dimensional (2D) van der Waals (vdW) moir\'e superlattices have provided a powerful knob to engineer a plethora of new quantum states. However, extending such moir\'e engineering to one-dimensional (1D) vdW systems has remained challenging. Here we report the moir\'e-engineered electronic insulating states in a new 1D moir\'e superlattice, by crystallographically aligning an armchair single-walled carbon nanotube (SWNT) to 2D hexagonal boron nitride (hBN) substrate. Remarkably, we observe the emergence of pronounced insulating states at charge neutrality point (CNP), full and half moir\'e fillings in lattice-aligned armchair SWNT/hBN heterostructures by low-temperature electrical transport measurements. In strong contrast, armchair SWNT devices without hBN alignment do not show any of these insulating behaviors, providing compelling evidence for the significant 1D moir\'e effect. Our density functional theory (DFT) and tight-binding calculations reveal that synergetic nanotube partial flattening and in-plane lattice reconstruction at 1D moir\'e interface expand the most stable AB' stacking regions (carbon on top of boron) and open sizable band gaps at both CNP and full moir\'e fillings at the single-particle level. Our one-body theory predicts no band gaps at half moir\'e fillings, suggesting that electron correlation and/or electron-phonon interaction may give rise to these emergent insulating behaviors in our 1D moir\'e systems. Our work establishes a new and definite moir\'e engineering route for 1D vdW materials and opens an exciting avenue for exploring interaction-induced quantum phases in 1D.