Novel transport phenomena in two-dimensional crystals beyond graphene

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Bon-Technical Abstract:Semiconductors have revolutionized out lives. Recently new types of semiconductors, such as single atomic layers of transition metal dichalcogenides and black phosphorus, have become available. This project studies several types of novel transport phenomena in these materials. These transport phenomena, such as collision-free ballistic transport and coherent plasma oscillation, play important roles in nanoscale electronic devices. This project provides fundamental information about these transport phenomena, and reveals rich physics involved in nonequilibrium transport in solids. Furthermore, the studies of several novel spin transport phenomena provide information for application of these materials in spin-based electronics. This project achieves broader impacts by training graduate and undergraduate students, involving K-12 teachers, broadening participation of underrepresented groups, and enhancing research infrastructure on nanotechnology and renewable energy technology. Technical Abstract:The scientific problem studied in this project is nonequilibrium ballistic charge and spin transport in two-dimensional crystals, including transition metal dichalcogenides and phosphorene. The methods and approaches of this project are based on three ultrafast laser techniques: a quantum interference and control technique that can instantaneously inject ballistic charge and spin currents, a differential pump-probe technique that can resolve sub-nanometer motion of electrons, and a second-harmonic generation technique for ultrafast and direct detection of the velocity of electrons. The goals of this project are to understand and control several novel transport phenomena in two-dimensional crystals, such as coherence plasma oscillation, ballistic charge transport, ballistic pure spin transport, spin Hall effect, spin-polarized charge transport, and spin Gunn effect.