Atomically thin crystals, such as layered transition metal dichalcogenides, provide a new platform to investigate optoelectronic spin systems and quantum photonics in low dimensional solid state systems. In these materials, the band extrema occur at two inequivalent momentum space valleys at the edges of the Brillouin zone. The valley degree of freedom, i.e., the location of an electron in momentum space, can therefore serve as a binary valley pseudospin, similar to spin in spintronics. Importantly, a valley dependent optical selection rule allows for optical control of the valley pseudospin. In this talk, I will discuss two optically driven valley pseudospin systems based on excitons (bound electron-hole pairs) in 2D semiconductors. First, I will discuss the physics and applications of 2D heterostructures composed of stacked monolayers of MoSe_2 and WSe_2 . These heterostructures host interlayer valley excitons where the electrons and holes are located in different layers. These spatially indirect excitons exhibit long lifetimes and valley polarization times which are promising for valley based information applications and for investigating long-range spin transport phenomena. Second, I will discuss single excitons localized to defects in monolayer WSe_2 , which are shown to be single photon emitters. I will discuss the physics of these localized quantum states as well as their potential quantum photonics applications. These localized quantum states host unique opportunities to study the hyperfine interaction in solid state systems, and potentially offer a new solid state quantum information platform.
John Schaibley was born and grew up in Indianapolis, Indiana. He attended Purdue University, where he received B.S. degrees in physics and mathematics, graduating Phi Beta Kappa with highest distinction. He did his graduate work at the University of Michigan under the guidance of Professor Duncan Steel, where his Ph.D. research focused on solid state spin-photon interfaces and quantum optics with single InAs quantum dots. At the University of Michigan, he received an M.S. in electrical engineering-optics and a Ph.D. in physics. During his graduate work, he received the American Association of Physics Teachers Outstanding Teaching Award, as well as the Peter Franken Award, which is awarded to an outstanding physics graduate student. He is currently finishing a postdoc at the University of Washington under Professor Xiaodong Xu, investigating fundamental light-matter interactions, device physics, and optical spin-valley effects in 2D materials and their heterostructures.
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MSEE 239, Purdue University, West Lafayette, IN