Materials Science Research Lecture
"Into the dark world of excitons in atomically thin semiconductors"
About a decade ago, the discovery of monolayers of transition metal dichalcogenides opened a new frontier in the study of optically excited states in semiconductors, and related opto-electronic technologies. These materials exhibit a plethora of robust excitonic states, such as bright excitons at the K & K' valleys, momentum- and spin-forbidden dark excitons, and hot excitons. Optics-based experiments have revealed much about the bright excitonic states, but they remain largely unable to access their valley character, their scattering channels into other valleys within the Brilloin Zone, and the nature of the dark states in these valleys.
Angle-Resolved Photoemission Spectroscopy (ARPES) based techniques would be ideal to access the valley character, and momentum-resolved scattering channels of photoexcited states in 2D semiconductors. But these are very challenging experiments to perform on the typically-available, micron-scale, 2D semiconductors. In today's talk, I will discuss the challenges involved, and progress made in my lab to date towards this aim. Any – time permitting – we will end with an entertaining peek into the ‘quantum psychology of dark excitons'!
More about the Speaker:
Keshav Dani is currently an Associate Professor at the Okinawa Institute of Science and Technology (OIST), Graduate University in Okinawa, Japan. He joined OIST in Nov. 2011 as a tenure-track Assistant Professor after completing a Director's Postdoctoral Fellowship at the Center for Integrated Nanotechnologies at Los Alamos National Laboratory. Keshav graduated from UC Berkeley in 2006 with a PhD in Physics, where he explored the nonlinear optical response of the quantum Hall system under the supervision of Daniel Chemla at LBNL. Prior to his PhD, he obtained a BS from Caltech in Mathematics with a senior thesis in Quantum Information Theory under John Preskill and Hideo Mabuchi. His current research interests lie in the use of ultrafast techniques to study electron dynamics of two-dimensional materials and energy materials, develop optoelectronic applications in the terahertz regimes, and pursue interdisciplinary projects with OIST colleagues in neuroscience and art conservation.
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