Spin–orbit coupling signatures in polycrystalline bismuth thin films

Bismuth is recognized as one of the elemental solids with the strongest intrinsic spin–orbit coupling (SOC) and is widely used to induce topological characteristics in hetero-structures, particularly in chalcogenide-based material systems. Precise control over the crystalline quality and phase purity of bismuth is crucial for its characteristic topological features which can be achieved via molecular beam epitaxy (MBE). In this work, we investigate the electronic transport properties of MBE-grown Bi thin films deposited on Si(111) substrates. Robust spin–orbit coupling is manifested through pronounced weak anti-localization features observed under both out-of-plane and in-plane magnetic fields. In addition, a planar Hall response consistent with Rashba-type SOC emerges at room temperature, underscoring the strong interfacial and structural asymmetry in these MBE-grown Bi films. These films display a temperature-driven sign reversal in the Hall carrier concentration, indicating a transition in the dominant carrier type. Collectively, these observations advance the fundamental understanding of SOC-mediated transport in low-dimensional Bi and open avenues for engineering Rashba-dominated states in functional hetero-structures.