Join us for the Physics Condensed Matter Seminar at 2:30 -3:00 pm
Title: Superexchange-induced valley splitting in two-dimensional transition metal dichalcogenides
Abstract: Breaking time-reversal symmetry via an external magnetic field or supporting magnetic substrate has been demonstrated to lift the degeneracy of the band gaps at the inequivalent K and K’ valleys in monolayer transition metal dichalcogenides (TMDs), a phenomenon known as valley splitting. However, reported valley splittings thus far are modest, and a detailed structural and chemical understanding of valley splitting via magnetic substrates is lacking. In this talk I will present results from my density functional theory (DFT) investigation of magnetic atoms in proximity to monolayer WSe2 and MoS2 TMDs to demonstrate the sensitivity of this phenomenon to the overlap of TMD Bloch states at the valley extrema with the localized d states of the magnetic atom. I will rationalize these results with a model Hamiltonian with second-order spin-dependent exchange coupling to demonstrate that valley splitting via magnetic substrates is driven by a superexchange mechanism. Finally, I will use these results to offer general design principles and propose optimal magnetic substrates for large valley splitting.
Elizabeth Peterson is a PhD candidate in the Physics Department at UC Berkeley. She received her Bachelors of Science degrees in Chemistry and Applied Mathematics at UCLA in 2013. From 2014-2016 she worked at StitchLabs, Inc., a technology start-up in San Francisco. She began her PhD studies at UC Berkeley in 2016. In 2021 Elizabeth was awarded the Kavli Energy NanoSciences Institute's Philomathia Graduate Student Fellowship. Her research interests include using first-principles computational condensed matter techniques to study 2D materials and metal oxides for applications in artificial photosynthesis and valleytronics technology.