Molecular beam epitaxy of quasi-1D α-Bi₄Br₄ nanoribbon/NbSe₂ heterostructures

Topological insulator/superconductor heterostructures provide an important platform for realizing Majorana fermions and topological quantum computation. However, there is a notable lack of studies on one-dimensional (1D) topological superconducting edge states. In this study, we employed molecular beam epitaxy to achieve controlled van der Waals epitaxial growth of quasi-1D α-Bi₄Br₄ nanoribbons on superconducting NbSe₂ substrates. Through comparison of two growth techniques—co-evaporation and two-step growth methods, we revealed the nanoribbon growth mechanisms and achieved high-quality nanoribbons with high crystallinity and uniform distribution. X-ray diffraction and photoelectron spectroscopy confirmed the (00l)-oriented growth of nanoribbons, while Raman spectroscopy verified the heterostructure formation. Notably, by precisely tuning growth parameters, we achieved controlled preparation of nanoribbons with varying thicknesses, laying a solid material foundation for investigating dimension-dependent topological properties in this system. Moreover, atomic force microscopy-infrared spectroscopy measurements revealed edge-localized optical absorption below the bulk bandgap (∼250 meV), providing experimental evidence for the existence of edge states. This work establishes an ideal platform for investigating 1D topological superconducting states and Majorana states, advancing prospects for topological quantum devices and computation.