Professor Felipe H. da Jornada

Stanford University

Friday, January 29

1:00 p.m.

Zoom

Understanding excited states in low dimensions for energy applications: from biexcitons to universal dispersionless plasmons

Modern parameter-free – or ab initio – computer calculations can accurately predict a large number of properties of materials with minimal to no experimental input. Still, the frontiers of these ab initio computational approaches need to be significantly expanded to explain novel and/or unusual electronic excitations, particularly in low-dimensional materials, such as monolayer transition metal dichalcogenides (TMDs), where weak electronic screening leads to strong many-electron interactions. In this talk, I present new perspectives to tackle some of these fascinating problems.

In this talk, I show how we can understand strongly bound multiparticle excitations such as trions and biexcitons – which involve the correlated motion of three and four quasiparticles, respectively. Our approach allows us to predict, without adjustable parameters, that trions and biexcitons in carbon nanotubes are stable at room temperature, and to reveal the complex valley and spin physics of such excitations in monolayer TMDs. We also apply these techniques to understand processes such as singlet fission (splitting one exciton into two) in organic crystals – a possible route to design solar cells with efficiencies beyond that of the Shockley-Queisser limit of 34%. Finally, we also explore another electronic excitation – plasmon – in low-dimensional materials. We show that plasmons in real quasi-2D metals display a unique but universal dispersion not found in the ideal 2D electron gas. I will show that quasi-2D metals can host long-lived plasmon excitations, yield giant electric field enhancement of the order of 107, and serve as platforms for practical applications involving light-matter interactions, such as photocatalysis.

Bio

Felipe H. da Jornada is an Assistant Professor in the Department of Materials Science and Engineering at Stanford University. Before joining the faculty in 2020, Felipe received his Ph.D. in physics from UC Berkeley working with Prof. Steven G. Louie, and he was awarded the best thesis award from the Kavli Energy NanoScience Institute at UC Berkeley (2017). Felipe’s previous research focused on understanding the electronic and optical properties of atomically thin materials – such as graphene and mono- and few-layer transition metal dichalcogenides (TMDs) – using first-principles computational approaches. He is currently interested in employing a combination of new theoretical formalisms and massively parallel computer calculations to understand new excited-state phenomena in materials with applications in energy research, physics at reduced dimensions, and quantum information.

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https://columbiauniversity.zoom.us/j/94074314952?pwd=RUVVN1RkK2duMW5RWlgzTmxRLzhxUT09

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