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Physics Department Colloquium
Multi-messenger scanning probe microscopy for the investigation of electronic properties of materials.
Date: Friday, February 3rd
Time: 3:30 pm
Place: 2241 Chamberlin Hall
Speaker: Victor Brar, UW Madison
Abstract: Scanning probe microscopy is an imaging technique whereby a sharp tip is moved across a surface while locally measuring some material property with a resolution that can be sub-Angstrom. A wide range of material properties can be studied in this way, including surface conductance (scanning tunneling microscopy), physical structure (atomic force microscopy), and surface potential (Kelvin probe force microscopy). By combining these measurement techniques, a complete understanding of a material's properties can be developed that relates electron motion to underlying atomic structure. In this talk I will show how multiple scanning probe measurements can be performed on graphene to reveal how electrons scatter off and move around in-plane potential barriers formed by charged defects. By comparing measurements of the spatially varying surface potential with measurements of the electron wavefunction, the electron dynamics can be modeled precisely, and described using a single-particle wavefunction. As the electron temperature is increased, however, these measurements reveal a new hydrodynamic phase of the electron fluid emerges with a viscosity comparable to diesel fuel. Our scanned probe measurements show that this new phase exhibits a conductivity that is greater than ballistic conductance, and that the motion of electrons around barriers resembles that of water moving around pebbles in a stream.
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