Quantum Octets in Air Stable High Mobility Two-Dimensional PdSe₂

Two-dimensional (2D) materials have drawn immense interest in scientific and technological communities, owing to their extraordinary properties that are profoundly altered from their bulk counterparts and their enriched tunability by gating, proximity, strain, and external fields. For digital applications, an ideal 2D material would have high mobility, air stability, sizable band gap, and be compatible with large-scale synthesis. Here we demonstrate air-stable field-effect transistors using atomically thin few-layer PdSe₂ sheets that are sandwiched between hexagonal BN (hBN), with record high saturation current >350 µA/µm, and field effect mobilities 700 and 10,000 cm²/Vs at 300K and 2K, respectively. At low temperatures, magnetotransport studies reveal unique octets in quantum oscillations, arising from 2-fold spin and 4-fold valley degeneracies, which can be broken by in-plane and

out-of-plane magnetic fields toward quantum Hall spin and orbital ferromagnetism.