Electronic metastability in a light-driven cuprate ladder

Ultrafast optical fields can drive quantum materials into dynamical states with emergent properties, but these nonequilibrium phases often decay rapidly, limiting their practical applications. In rare instances, photoinduced states evade relaxation, becoming metastable via trapping in classical free energy minima, stabilized by cooperative lattice deformations. Is it possible to instead achieve metastability by electronic means? While this is the topic of extensive theoretical discussion, it remains unexplored experimentally. In this talk, I will present our recent observation of electronic metastability in Sr14Cu24O41, a one-dimensional cuprate ladder compound. Following intense optical excitation, we observe a metastable state persisting to several nanoseconds, three orders of magnitude longer than typical light-induced nonequilibrium phenomena. Employing time-resolved terahertz and resonant x-ray spectroscopy measurements, we find that this occurs via a sudden transfer of holes, from chain-like charge reservoirs into the ladders, where they remain trapped, without a detectable structural distortion. The metastability is the consequence of the transient activation of a chain-to-ladder tunneling pathway, which is otherwise symmetry-forbidden, protecting the nonequilibrium charge distribution from decay. Our findings establish a symmetry-based, electronic route towards achieving long-lived light-driven phases in quantum materials.