- Friday, November 16, 2018 from 4:00pm to 5:00pm
- Barnard Hall, 103 - view map
In the past decade, interest has been renewed in 2D and quasi-2D layered materials, which were initially explored in their 3D bulk form more than 50 years ago. To name just two examples: molybdenum disulfide, a layered transition metal dichalcogenide widely used as a lubricant, exhibits optical properties that are dominated by many-body physics, even at room temperature, when reduced to a single atomic layer. Bismuth selenide, formerly known mainly as a semiconductor for thermoelectrics, is nowadays famous for being a topological insulator, where global crystal symmetry dictates that the surface is conductive, while the bulk is insulating.
In these 2D layered materials, extreme quantum confinement, reduced symmetries and strong spin-orbit interactions give rise to a complex zoo of emergent quantum phenomena. Recent efforts have been devoted to exploring and ultimately controlling such quantum properties by engineering these materials with atomistic precision.
In my talk, I will introduce the particular optical and electronic properties of 2D layered materials, and I will discuss recent advancements towards an atomistic understanding of the correlation between local electronic and optical properties. In particular, we use combined atomic force and scanning tunneling microscopy to unambiguously identify single point defects in 2D materials and characterize their electronic properties.  Using nanoscale photoemission spectroscopy, recently developed at Berkeley Lab, we are able to locally resolve electronic band structure and chemical composition of 2D materials with a resolution down to 150 nm. A direct correlation with optical spectroscopy yields detailed insights into the interplay between material properties, such as composition or defect density, and excitonic physics at the nanoscale.  By contrast, symmetry protected topological phenomena are robust against local perturbations, and they enable optical control of spin currents in layered materials. 
- Department of Physics