Wednesday, October 16, 2019
Condensation - the familiar process underlying the formation of clouds and the distillation of ethyl alcohol into whiskey - is the phase transition of gas into liquid droplets. In semiconductors, at sufficiently high electron-hole (e-h) densities or low temperatures, the gas of non-equilibrium electrons and holes may undergo condensation into one of several potential liquid-like phases. In this talk, I present recent results on the gas-to-liquid phase transition of electrons and holes in ultrathin van der Waals heterostructure photocells revealed through multi-parameter dynamic photoresponse microscopy (MPDPM). By combining rich visualization with comprehensive analysis of very large data sets acquired through MPDPM, we find that ultrafast laser excitation at a graphene-molybdenum ditelluride-graphene interface leads to the abrupt formation of ring-like spatial patterns in the photocurrent response as a function of increasing optical power. These patterns, together with extreme sublinear power dependence and picosecond-scale photocurrent dynamics, provide strong evidence for the formation of a two-dimensional e-h liquid. While our imaging experiments mark the first observation (in over 50 years of study) of an e-h liquid at room temperature, I will discuss our results within the greater context of strongly correlated electronic condensates.
Bio: Having established himself as a rising leader in quantum optoelectronics research at Cornell University (PhD Physics 2011) and MIT (Postdoctoral Fellow Physics), Prof. Nathaniel Gabor began his academic career at the University of California Riverside in 2013. Nathaniel’s research focuses on quantum optoelectronic measurements of nanoscale materials and has led to the direct observation of highly efficient electron-hole pair multiplication in carbon nanotubes and the unusual hot carrier transport regime in graphene. He has also established leadership in the design and understanding of advanced energy harvesting and storage technologies, having been recognized with numerous national and international awards. Based on several key discoveries regarding light harvesting in biology, Prof. Gabor was named a Scialog Advanced Energy Storage Fellow by the Research Corporation for Science Advancement, as well as a CIFAR Azrieli Global Scholar within the Canadian Institute for Advanced Research. With successful funding as a NSF Career Award, AFOSR Young Investigator Program (YIP) Award, and Presidential Early Career Award in Science and Engineering (PECASE) recipient, his multi-disciplinary research focus has enabled him to pursue scientific topics ranging from electronic liquids to viper vision.