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Colloquium: Seeing and controlling electrons in flatland

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Jie Shan, The Pennsylvania State University
01 September 2016 from 4:00 PM to 5:00 PM
117 Osmond Laboratory
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Confined in a two-dimensional (2D) plane, electrons are known to exhibit many intriguing physical phenomena. Atomically thin crystals such as graphene and transition metal dichalcogenides (TMDs) have emerged as a new class of 2D systems. As in any nanoscale systems, Coulomb interactions between charge particles in two dimensions are particularly strong due to the significantly reduced dielectric screening. Furthermore, because of symmetry, electrons in gapped graphene and single-layer TMDs possess a new two-fold valley degree of freedom (DOF) corresponding to the K and K’ valleys of the Brillouin zone.  Like the electron spin DOF, the valley DOF carries orbital magnetic moment and forms the basis for valley-based electronics and optoelectronics devices.  The presence of valley contrasting Berry curvatures, which can couple to external electromagnetic excitations, has also enabled the control of the valley DOF. In this talk, I will present our recent optical spectroscopy and microscopy studies on single- and few-layer samples of semiconductor TMDs. I will discuss interesting phenomena arisen from the Berry curvature and strong interaction effects.