Nonlinear Carrier Dynamics and Optical Response of Lanthanum-Doped Barium Stannate.

Lanthanum-doped barium stannate (LBSO) is an emerging transparent conducting oxide with high carrier mobility and tunable plasmonic properties in the infrared regime. In this work, we investigate the nonlinear electromagnetic response of LBSO using a linearized collisionless Boltzmann model that captures the field-induced modification of the carrier distribution function. We experimentally realize LBSO thin films with controlled carrier concentration and optical properties tailored for epsilon-near-zero operation. Analytical expressions for the nonlinear plasma frequency and permittivity reveal their dependence on carrier concentration, temperature, and optical excitation. An excitation-driven reduction in the effective plasma frequency is accompanied by significant changes in the permittivity spectrum. The results demonstrate that the LBSO metasurface exhibits strong optical tunability under near-infrared excitation, with significant modulation of its reflection and transmission characteristics. These findings provide physical insight into the nonlinear carrier dynamics in LBSO and establish a framework for designing tunable photonic devices based on transparent conducting oxides.