Hari Padma (CWRU Physics)

Date: Thu. February 26th, 2026, 4:00 pm-5:00 pm
Location: Rockefeller 301
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Decoding light-driven quantum materials with x-rays

Driving quantum materials with intense optical pulses offers a powerful means to control their behavior, leading to remarkable emergent phenomena such as photo-induced magnetic, ferroelectric, and superconducting phases. However, such phenomena are usually transient, limited to the sub-picosecond duration of the optical pulse or decaying shortly thereafter. Advancing the design and control of light-driven quantum materials therefore requires targeted strategies to achieve long-lived, metastable phases. In this talk, I will describe how symmetry protection leads to electronic metastability in a prototypical cuprate ladder material, Sr 14 Cu 24 O 41 . This finding is enabled by femtosecond resonant x-ray spectroscopy, which provides unprecedented access to correlated electronic phenomena far from equilibrium. Our measurements show that the metastability is driven by a transfer of holes from chain-like charge reservoirs into the ladders. This ultrafast charge redistribution arises from the optical dressing and activation of a hopping pathway that is otherwise forbidden by symmetry. Relaxation back to equilibrium is hence suppressed once the optical pulse ceases. Remarkably, we find that this trapped non-equilibrium electronic distribution hosts a propagating, collective charge mode that is absent at equilibrium, representing a possible precursor to superconducting pairing. Our results demonstrate how dressing quantum materials with electromagnetic fields can provide a rational design strategy for non-equilibrium phases of matter.

1. H. Padma, et al. Symmetry-protected electronic metastability in an optically driven cuprate
ladder, Nature Materials 24, 1584 (2025)
2. H. Padma, et al. A light-induced charge order mode in a metastable cuprate ladder, arXiv:2510.24686
(2025)
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Bio: Hari Padma is an experimental condensed matter physicist and an Assistant Professor in the Department of Physics at Case Western Reserve University. His research is centered on probing and controlling quantum materials at femtosecond timescales using electromagnetic fields. Prior to joining the faculty at Case, he was a Postdoctoral Fellow in the Department of Physics at Harvard University. He earned his Ph.D. in Materials Science and Engineering from Penn State University, where he developed magneto-optic spectroscopic tools to identify hidden exchange pathways in magnetic topological phases. His current work aims to advance ultrafast THz and resonant x-ray methods to create and stabilize emergent non-equilibrium phases in quantum materials.