QuMat seminar

Chiroptical probes to track spin & light polarization in space & time in emerging semiconductors Speaker: Sacha Feldmann – Laboratory for Energy Materials at EPFL Host: Daniel Vanmaekelbergh

Abstract:

Solution-processable semiconductors like halide perovskites and certain molecules are promising for next-generation spin-optoelectronic applications [1]. Yet, we don’t fully understand what governs the excitation and spin dynamics in these materials, and even less how these are affected by chirality.

In this talk, I will give an overview of our recent efforts to understand the spin-optoelectronic performance of these materials through time-, space- and polarization-resolved spectroscopy and microscopy.

For halide perovskite films, I will first show that energetic disorder strongly modulates their charge dynamics [2,3]. By pushing broadband circular dichroism to diffraction-limited spatial and 15 fs time resolution, we then create a spin cinematography technique to witness the ultrafast formation of spin domains in these films due to local symmetry breaking and spin-momentum locking [4].

I will then briefly explain the fundamentals and artifacts involved in measuring circularly polarized luminescence (CPL) reliably and introduce an open-access methodology and code to do so [5], and finally show our most recent development of a transient broadband full Stokes-vector polarimetry with unprecedented time- and polarization resolution to track the emergence of chiral light emission [to be submitted].

[1] Nature Reviews Materials 8, 365 (2023)
[2] Nature Photonics 14, 123 (2020)
[3] Nature Materials 21, 1388 (2022)
[4] Nature Materials 22, 977 (2023)
[5] Advanced Materials 35, 2302279 (2023)



The Feldmann Lab at EPFL develops and employs ultrafast magneto-chiroptical spectroscopy to understand the next generation of soft semiconductors. The overarching goal is to maximize energy efficiency for a sustainable future by unlocking applications ranging from flexible light-weight solar cells & displays all the way to entirely new applications in quantum information processing.

Sascha studied Chemistry at Heidelberg University (Germany) and completed his Ph.D. in Physics at the University of Cambridge (UK) in 2020, where he continued to work as an independent EPSRC Doctoral Prize Fellow. In July 2022, Sascha started his own group at Harvard University through a Rowland Fellowship and in September 2023 was appointed tenure-track Assistant Professor and Head of the Laboratory for Energy Materials at EPFL (Switzerland). He remains affiliated as SCR member of Winthrop House at Harvard.

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