Excitonic devices based on 2D semiconductor heterostructures

2nd September 2020

Timing : 1 pm EST

For zoom link to the talks, please email mjgc@mit.edu with your institute email and mention affiliation


For a list of all talks at the NanoBio seminar Series 2020, see here


The discovery of graphene marked the start of research in 2D electronic materials which was expanded in new directions with MoS2 and other layered semiconducting materials. They have a wide range of interesting fundamental properties and potential applications. New opportunities are enabled by the band structure of transition metal dichalcogenides (TMDCs) in which we could harness the valley degree of freedom for valleytronics and next-generation photonics. Long-lived interlayer excitons in van der Waals heterostructures based on TMDCs have recently emerged as a promising platform for this, allowing control over exciton diffusion length, energy and polarisation. I will show here how by using MoS2/WSe2 van der Waals heterostructures, we can realize excitonic transistors with switching action, confinement and control over diffusion length at room temperature in a reconfigurable potential landscape. On the other hand, the weak interlayer interaction and small lattice mismatch in MoSe2/WSe2 heterostructures results in brightening of forbidden optical transitions, allowing us to resolve two separate interlayer transitions with opposite helicities and meV-scale linewidths. These have opposite helicities under circularly polarized excitation, either preserving or reversing the polarization of incoming light. By using externally applied electrical fields, we can control their relative intensities and polarisation by different regions in the moiré pattern, characterized by different local symmetries and optical selection rules. Our more advanced excitonic devices now also offer the way to manipulate the motion of valley (spin) polarized excitons.



Snow
Andras Kis
Associate Professor, EPFL
Laboratory of Nanoscale Electronics and Structures


Andras Kis is an Associate Professor in Electrical Engineering at EPFL, Lausanne. He started his research group in 2008 and has made fundamental contributions to the study of the electronic properties of 2D materials and atomically thin TMDCs. His pioneering work on MoS2 transistors was the first demonstration of high-quality device on a 2D semiconductor and has been cited over 10’000 times. Andras Kis is also serving as the editor in chief of the Nature partner journal 2D materials and applications and is a highly cited researcher. Prior to joining EPFL as faculty, Kis was a postdoctoral researcher at UC Berkeley in the group of Alex Zettl. He received his Ph.D. in physics from EPFL in 2003 and received his MSc in physics from the University of Zagreb, Croatia. His major awards include the Latsis prize in 2004, ERC starting grant in 2009 and ERC consolidator grant in 2015.