Bi₄Br₄ is a quasi-one-dimensional van der Waals topological insulator with novel electronic properties. Several efforts have been devoted to the understanding of its bulk form, yet it remains a challenge to explore the transport properties in low-dimensional structures due to the difficulty of device fabrication. Here we report for the first time a gate-tunable transport in exfoliated Bi₄Br₄ nanobelts. Notable two-frequency Shubnikov–de Haas oscillations oscillations are discovered at low temperatures, with the low- and high-frequency parts coming from the three-dimensional bulk state and the two-dimensional surface state, respectively. In addition, ambipolar field effect is realized with a longitudinal resistance peak and a sign reverse in the Hall coefficient. Our successful measurements of quantum oscillations and realization of gate-tunable transport lay a foundation for further investigation of novel topological properties and room-temperature quantum spin Hall states in Bi₄Br₄.

Coupling topological surface states with superconductivity provides a powerful route to realizing a topological superconducting phase that can host Majorana zero modes and support fault-tolerant topological quantum computation. Here, we report proximity-induced two-dimensional superconductivity in a TaIrTe4/NbSe2 heterostructure, where superconductivity is induced into the surface of the type-II Weyl semimetal TaIrTe4. Differential resistance spectra reveal pronounced subgap oscillations, indicating multiple induced superconducting gaps associated with the coexistence of electron and hole Fermi pockets in TaIrTe4. The induced superconductivity exhibits strong anisotropy: while a modest out-of-plane magnetic field is sufficient to suppress the superconducting state, the in-plane upper critical field remains much higher and exceeds the Pauli limit below 2.7 K. Angular-dependent upper critical field measurements reveal a distinct Tinkham-like cusp, together with the Berezinskii–Kosterlitz–Thouless transition, confirming the two-dimensional nature of the induced superconductivity. These results establish TaIrTe4/NbSe2 heterostructure as a versatile platform for exploring superconductivity mediated by topological surface states in type-II Weyl systems.