Quantum oscillations in a Bi thin film grown by molecular beam epitaxy: evidence for two-dimensional transport

Bismuth (Bi), with its strong spin–orbit coupling and complex band structure, has long been of both fundamental and technological interest. The topological nature of Bi remains under debate, as its small band gap at the M point of the Brillouin zone allows band inversion—and hence the emergence of topological character—under strain or quantum confinement. Although quantum oscillations have been extensively studied in bulk Bi, their observation in epitaxial thin films has been limited due to challenges in achieving the structural quality required for coherent transport. Here, we overcome these limitations by careful growth studies and report clear Shubnikov-de Haas (SdH) oscillations in a high-quality, 10-nm-thick Bi(001)_H thin film grown on a GaSb(111)B substrate by molecular beam epitaxy. Well-defined quantum oscillations emerge under perpendicular magnetic fields, exhibiting a frequency of approximately 30 T and persisting up to 50 K, corresponding to an effective mass of ~0.05 mₑ which is significantly smaller than the value reported for bulk Bi (~0.2 mₑ) in earlier studies. The angular dependence of the oscillations follows a 1/cosθ relation, indicating a predominantly two-dimensional origin. The sheet resistivity increases with decreasing temperature, confirming semiconducting behaviour from reduced band overlap. At low temperatures, the transverse magnetoresistance shows a non-linear positive slope, characteristic of hole-dominated mixed-carrier transport and the multivalley band structure of Bi. The observed oscillations are likely associated with surface states in the thin-film limit, establishing a promising platform for exploring confinement and strain-induced topological transitions in elemental Bi.