Giant Tunability of Electronic Properties of High Mobility Two-Dimensional Semiconductors

Few-layer metal chalcogenides are promising material platforms for electronic, optoelectronic, and thermal applications, due to their high mobility, substantial band gap, and demonstrated synthesis in the wafer scale. Here I will present our recent work in two members of the material family with unprecedented mobility. In few-layer InSe quantum wells, we demonstrate electrostatic population and characterization of the second subband, with giant tunability of its energy, population, and spin-orbit coupling strength, via the control of not only layer thickness but also out-of-plane displacement field. A modulation of as much as 350% or over 250 meV is achievable, underscoring the promise of InSe for tunable infrared and THz sources, detectors and modulators. Moreover, for few-layer PdSe₂ field effect transistors, we demonstratde large saturation current >350 mA/mm, and high field effect mobilities of ~ 700 and 10,000 cm²/Vs at 300K and 2K, respectively. At low temperatures, magnetotransport studies reveal unique octets in quantum oscillations that persist at all densities, 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.