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Materials Science at Oregon State University

Graphene Micro-Femto Energetics

Date: Thursday, Jan 23rd
Presenter: Prof. Matt Graham, OSU Physics Department


When bulk carbon is reduced to nanoscale dimensions many-body interactions and correlations are remarkably enhanced, drastically changing the optical and electronic properties in highly unpredictable ways. In 2D materials like graphene, electronic correlations result in high electron mobility, but very short e-h lifetimes. We develop a combined transient absorption-TEM technique that relates the site-specific electron relaxation dynamics to the atomic structure. This provides time-space microscopy movies of the electronic population. Through this technique we provide evidence for tuneable bound-exciton states in twisted bilayer graphene. By fabricating graphene p-n junctions, we further study how electrons relax near the Fermi energy. Specifically we time-resolve the photocurrent generated, which functions as an ultrafast electron temperature thermometer. These novel photocurrent measurements reveal electrons relax by a radically accelerated “supercollision” mechanism. This mechanism provides the missing link to predict current production from light absorption in graphene.