Competing Auger-Like and Intraband Excitations Drive Anomalous Modulations in Indium Tin Oxide

Anthony C Harwood; Sean Z J Lim; T V Raziman; Yan Li; Joseph Stones; John W G Tisch; Simon A R Horsley; Stefano Vezzoli; John B Pendry; Riccardo Sapienza

arXiv · 2605.21432

Competing Auger-Like and Intraband Excitations Drive Anomalous Modulations in Indium Tin Oxide

Anthony C Harwood·Sean Z J Lim·T V Raziman·Yan Li·Joseph Stones·John W G Tisch·Simon A R Horsley·Stefano Vezzoli·John B Pendry·Riccardo Sapienza

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Abstract

Transparent conducting oxides near their epsilon-near-zero frequency exhibit near-unity ultrafast modulations of the refractive index which have enabled the field of time-varying metamaterials, yet the underlying carrier dynamics at high driving fluences remain poorly understood. Here, we report ultrafast modulations in the reflectivity and transmissivity of indium tin oxide, and a non-monotonic oscillatory behavior. This is especially evident in the time evolution of the complex Fresnel coefficients retrieved directly from pump-probe spectrograms using an optical gating technique, GRUMPY FROG. The dynamics of the retrieved plasma frequency and damping coefficient are well captured by an extended two-temperature model incorporating a competing nonlinear interband process: at high fluences, Auger-type scattering of hot conduction electrons promotes valence band carriers, increasing the plasma frequency while accelerating hot-electron cooling and raising the damping coefficient. These results clarify the origin of anomalous high-fluence dynamics in indium tin oxide and identify a fluence-tuneable modulation dynamic with direct implications for ultrafast refractive index engineering in time-varying photonic devices and optical switching.

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Anthony C Harwood, Sean Z J Lim, T V Raziman, Yan Li, Joseph Stones, John W G Tisch, Simon A R Horsley, Stefano Vezzoli, John B Pendry, Riccardo Sapienza. 2026-05-20. Competing Auger-Like and Intraband Excitations Drive Anomalous Modulations in Indium Tin Oxide. https://arxiv.org/abs/2605.21432

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