Epitaxial growth of Bi nanowires on Pb-$\sqrt{7}\times \sqrt{3}$ surface

Confining particles in one-dimensional (1D) systems profoundly modifies their electronic behaviors, which have been extensively demonstrated in carbon nanotubes and atomic chains. Structural instabilities and electron localizations often dominate the conductivity of 1D nanowires. Here, we successfully grew Bi single nanowires and nanowire arrays on Pb-$\sqrt{7}\times \sqrt{3}$ substrates via molecular beam epitaxy, both of which exhibit metallic behavior. Using scanning tunneling microscopy and first-principles density functional theory calculations, the interwire coupling and the correlation between nanowire bundles and electronic properties are investigated. A characteristic peak at 0.75 eV is observed on single wires and wire bundles of up to four nanowires, whereas interwire coupling weakens it and makes it disappear for wire bundles of five and above. These findings illustrate that the interwire coupling plays a critical role in the electronic structure of the 1D system, which provides insights for the design of nano-electronics materials.