Figure 1. (a) Sketch of the THz excitation of a deep localized vacancy forming metastable polaronic state requiring ≈ 1 ns before relaxing back to the vacancy site; (b) Transient reflectivity measured by THz pump/1560 nm (upper panel) and 780 nm (lower panel) probe spectroscopy on a representative TiO2-x sample; (c) Variation (colored) of the steady-state optical conductivity of same sample used in (b) to that simulated after a THz pump excitation. The bottom panel shows the corresponding calculated transient reflectivity. The yellow vertical lines indicate the two employed probe frequencies. Adapted from Phys. Rev. Research 7, 023011 (2025). P. Di Pietro1, J. Schmidt1, N. Adhlakha1,2, S. K. Chaluvadi3, F. Mazzola3,4 V. Stopponi3, L. Tomarchio5, P. Orgiani3, S. Lupi3, A. Perucchi1 1 Elettra - Sincrotrone Trieste S.C.p.A, Trieste, Italy 2 Department of Physics, National Institute of Technology Karnataka, Surathkal, Mangalore Karnataka, India 3 CNR-IOM, TASC Laboratory, Trieste, Italy 4 CNR-SPIN, c/o Complesso di Monte S. Angelo, Napoli, Italy 5 Physics Department, “Sapienza” University of Rome, Rome, Italy e-mail: paola.dipietro@elettra.eu Original paper P. Di Pietro et al., Phys. Rev. Research 7, 023011 (2025); DOI:https://doi.org/10.1103/ PhysRevResearch.7.023011. a) b) c) Fig. 1 Functional materials Elettra Highlights 2024–2025 37
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