Pursuing novel electronic states in two-dimensional systems

Speaker: 
Ke Zou
Event Date and Time: 
Thu, 2017-05-04 11:00 - 12:30
Location: 
Hennings 318
Local Contact: 
Leanne Ebbs
Realizing enhanced or novel electronic states in 2-dimensional (2D) materials with atomic thickness, which result from reduced dimensionality and interfacial interactions with the nearby substrate, is of great interest from both fundamental and technological perspectives. Two examples showing we achieve enhanced superconductivity in monolayer FeSe and a tunable band structure in bilayer graphene, respectively, will be presented in the seminar. The marked enhancement of the superconducting critical temperature for monolayer FeSe grown on SrTiO3 is a notable recent discovery in the field of high temperature superconductivity. We determine the surface structure of SrTiO3 that is used to achieve superconducting FeSe films in experiments. The existence of a double TiO2 layer helps to transfer electrons to FeSe films, and leads to a band structure characteristic of superconducting samples. The characterization of the interface structure presented here is a key step towards the resolution of many open questions about this superconductor. Additionally, monolayer graphene, despite its unique electronic and optical properties, has no band gap, which greatly limits its applicability where semiconductors are required. By breaking the layer symmetry in bilayer graphene, we are able to open and control a band gap. Localized states produced by potential fluctuation in the oxide substrate play a crucial role in the electrical transport of bilayer graphene. The model we construct may be generalized for other 2D materials on common oxide substrates.
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